Synthesis, processing and characterization of nanoscale multi functional oxide films VII

Resume : Two-dimensional electron gases (2DEGs) at oxide interfaces, as LaAlO3/SrTiO3 (LAO/STO) and its several variants, show multiple functional properties of major physical interest, including a high low-temperature mobility, superconductivity, a large Rashba spin-orbit coupling, an exceptionally large spin-to-charge conversion efficiency and a yet controversial magnetic ground state. Such properties are tunable under external control parameters, as electric field effect. In a number of experiments briefly described in the talk, we will first show the capability of tailoring unexpected samples properties by pushing growth control of our crystalline interfaces to the highest level. We will then focus on the control of strain relaxation, selecting the conditions in which an epitaxially strained state is retained much above the expected critical thickness. In this regime, strain relaxation is highly disruptive and surprisingly causes the formation of freestanding LAO/STO membranes, which preserve the metallic properties of macroscopic LAO/STO samples. Such membranes can be manipulated, contacted and employed as elements of microscopic circuits on a generic surface.

Resume : Two-dimensional electron gases (2DEG) at the interface between two wide bandgap oxide materials have attracted a lot of interest in the past decade, both due to the promise to realize novel electronic devices and also because of interesting new physical phenomena. In case of the famous prototypical LaAlO3/SrTiO3 system it is believed that the polar discontinuity and an electronic reconstruction at the n-type LaO-TiO2 interface are the origin of the 2DEG. Recently, BaSnO3 is intensively investigated due to its highest electron mobility at room temperature (~300 cm2/Vs) among other transparent conductive oxides even for a doping concentration of 1E20 cm-3. Similar to the LaAlO3/SrTiO3 case a 2DEG is observed when growing a LaInO3 film on a BaSnO3 buffer. By means of transmission electron microscopy we found that an interface roughness of even several nanometers and a variation of the cation termination at the LaInO3/BaSnO3 interface do not prevent the formation of the 2DEG. This surprising result raised the assumption that a more fundamental mechanism independent of the interface chemistry is responsible for the appearance of the 2DEG. Further analysis showed that the change of the tilt of oxygen octahedra from the cubic BaSnO3 (no tilt) to the bulk value of LaInO3 (5.5°) does not occur abruptly at the interface, but gradually within a few monolayers in LaInO3. The suppression of octahedral tilt leads to an interfacial polarization which in turn explains the formation of the 2DEG.

Resume : Metal/ferroelectric/metal (M/FE/M) junctions suffer from two interface controlled limiting factors: an interface FE dead layer, due to depolarizing field, and a high leakage current due to insufficient Schottky barrier height (SBH). Band engineering, developed in the 70s, is an effective way to control SBH at M/semiconductors junctions. Since then DFT calculations have shown that interface chemical bounding plays a major role on both SBH [1] and polarization stabilization [2] at M/FE. We propose to apply these concepts to promote electrical polarization and control the SBH at the interfaces of epitaxial oxide FE junctions using interface engineering by combinatorial pulsed laser deposition. Modulation of the interface composition over a few monolayers (ML) tunes the FE’s electronic affinity and band gap, and the electrode’s work function and carrier doping, parameters which control bands alignment at the interface. We report here on La0.7Sr0.3MnO3/La1-ySryMnO3 (3ML)/SrTiO3 and La0.7Sr0.3MnO3/Ba1-xSrxTiO3 (1-3ML)/SrTiO3 junctions. Photo electron spectroscopies (XPS/UPS) showed a continuous La1-ySryMnO3 work function variation with the carrier content y. Local electrical UHV SPM characterizations (IVs, KPM), carried out without sample exposure to air, revealed a non-monotonous and correlated dependence of both the threshold voltage and the Kelvin potential. Effects of the interface chemical modulation on the band structure will be discussed versus composition and thickness. References: [1] R. Tung, Mat. Sci. and Eng. R 35, 1 (2001) [2] M. Stengel et al., Nat. Mat. 8, 392 (2009)

Resume : Magnetic or electronic properties of oxide thin films depend on the local structure and chemistry of the layers. For instance, cation ordering, antiphase boundaries or strain state can modify the saturation magnetization or the coercive field. Transmission electron microscopy (TEM) is one of the suitable technique to get access to structural and chemical mapping at the nanometer scale. The combination of several TEM techniques with atomic resolution is available to elucidate the correlation between structure/chemistry and physical properties. The first study will focus on ferromagnetic spin filters that rely on the spin-dependent transmittance of ferromagnetic tunnel barriers due to the existence of an exchange-split band gap. Several requirements have to be fulfilled by the barrier to be efficient: the magnetism has to remain important even at room temperature and for very thin thickness (down to 3nm) to allow for spin-dependent tunnel transport. The second study will focus on the SrTiO3 / LaAlO3 system for transport applications. The occurrence of a conductive behaviour of the LaAlO3/SrTiO3 interface is attributed to the advent of an electronic reconstruction above a critical thickness of 4 u.c. of LaAlO3, in order to compensate the charge discontinuity at the interface between a polar (LaAlO3) and a non-polar (SrTiO3) materials. Various parameters are likely to affect the properties of this interface such as the change in the nature of the substrate, the application of a stress field or the introduction of slight chemical modifications in the layer or at the interface.

Resume : Quantum nanostructures open a window for solid-state research due to their fascinating possibilities to create novel electron systems. Electron states and correlation of quantum matters can be influenced by changing dimensions because of size quantisation effects. Among them, the zero-dimensional electron system (artificial atoms or quantum dots) is a cutting-edge research field with remarkable scientific advances. Confinements in three dimensions can bring intriguing electrical and optical properties, which play a key role in novel applications like fabrication of quantum photonic devices. Thus, their nanoscale structural explorations are essential for understanding the underlying physical properties, but rather challenging and rarely reported. Here, pulsed layer deposition has been used to epitaxially grow SrRuO3 thin films on SrTiO3 substrates, which are ultimately patterned to artificial atoms by using ion milling and e-beam lithography. By using aberration-corrected scanning transmission electron microscopy, we have performed atomic-scale microstructural investigations of the patterned SrRuO3 artificial atoms with different diameters. Atomically resolved high-angle annular dark-field imaging of the atoms’ cross-section enables us to study the evaluation of the strain states by applying geometry phase analysis. We unambiguously demonstrate that epitaxial strain of SrRuO3 artificial atom is gradually released while reducing the size of SrRuO3 artificial atoms.

Resume : Expansion of oxide thin films induced by changes in temperature and/or oxygen partial pressure pO2, known as chemical expansion, may contribute to the degradation of high-temperature fuel cells or enable a new generation of very high-temperature actuators with operating temperatures above 500°C. The phenomenon is investigated using thin-film praseodymium cerium oxide (Pr0.1Ce0.9O(2-δ), PCO) as model system. The chemical expansion of 300 nm to 2 µm thick films is measured by laser vibrometry at temperatures up to 800°C. The films are deposited onto yttria stabilized zirconia (YSZ) substrates that enable removal of oxygen by application of moderate pump voltages of up to about 1 V. The chemical expansion is correlated with the oxygen deficit δ that determines, in turn, the valence state of the Pr cations in the film. PCO is a favorable model material as it reversibly releases a substantial amount of oxygen under readily accessible oxygen partial pressures close to that of air. Chemical expansion also leads to lateral stress in the PCO film that leads to measurable deflection of the YSZ substrate. The superposition of expansion and deflection, i.e. the total vertical displacement, is investigated in-situ by high-temperature laser Doppler vibrometry (LDV). The measured chemical expansion correlates well with defect chemical and kinetic models and their expected dependence on temperature, oxygen pumping time and pumping voltage.

Resume : Piezoelectricity, a phenomenon known for centuries, is an effect that is about the production of electrical potential in a substance as the pressure on it changes. For wurtzite structures such as ZnO, GaN, InN and ZnS, due to the polarization of ions in a crystal that has non-central symmetry, a piezoelectric potential (piezopotential) is created in the crystal by applying a stress. The effect of piezopotential to the transport behavior of charge carriers is significant due to their multiple functionalities of piezoelectricity, semiconductor and photon excitation. By utilizing the advantages offered by these properties, a few new fields have been created. Electronics fabricated by using inner-crystal piezopotential as a “gate” voltage to tune/control the charge transport behavior is named piezotronics, with applications in strain/force/pressure triggered/controlled electronic devices, sensors and logic units. This effect was also extended to 2D materials such as MoS2. Piezo-phototronic effect is a result of three-way coupling among piezoelectricity, photonic excitation and semiconductor transport, which allows tuning and controlling of electro-optical processes by strain induced piezopotential. The objective of this talk is to introduce the fundamentals of piezotronics and piezo-phototronics and to give an updated progress about their applications in energy science (LED, solar) and sensors (photon detector and human-CMOS interfacing). [1] Wu, et al Science, 340 (2013) 952-957. [2] Pan et al. Nature Photonics, 7 (2013) 752-758. [3] Z.L. Wang Nano Today, 5 (2010) 540-552. [4] Yang et al. Nano Letters, 11 (2011) 4012–4017. [5] Wu et al. Nature, 514 (2014) 470-474. [6] W.Z. Wu and Z.L. Wang, Nature Review Materials, 1 (2016) 16031 [7] “Piezotronics and Piezo-phototronics with the Third-generation Semiconductors”, MRS Bulletin, 43 (2018) 922-926

Resume : Vanadium dioxide (VO2) has the remarkable property of exhibiting a first order insulator to metal transition (MIT) at a temperature T(MIT) close to ambient temperature (68°C). It is characterized by a crystallographic transformation from the high-temperature tetragonal rutile (R) to low-temperature monoclinic (M) structure and by a change in resistivity (of the order of 4 to 5 orders of magnitude) and optical transmission in the near-infrared range under the effect of an external stimulus such as heat, stress, current or electrical voltage. These properties give the thin film an ideal choice for applications in electronic devices as intelligent materials. Mechanism involved in decreasing T(MIT) in VO2 by selective doping is still a matter of debate. Our work focuses in the understanding of the correlation between W doping and the T(MIT), the electronic and geometrical structures around V atoms in V(1-x)WxO2 pulsed laser deposited thin films. Electronic (resistivity by four points probe) and structural (Raman spectroscopy) measurements revealed a reduction in T(MIT) by 35 to 60°C by increasing W doping from 1.3 to 3.3%. Clear evidence of substitutional W-doping on the crystallographic and electronic structure is observed both on the XANES and XAFS signatures.

Resume : Bulk p-wave triplet superconductivity is rare, but the important highly unconventional superconductor Sr2RuO4 (SRO) is the best known example and has been the subject of extensive study over the past decade and half [1]. Bulk p-wave superconductivity is extremely sensitive to electron scattering which has meant that the growth of superconducting SRO thin-films has been extremely challenging [2,3]. Two papers report superconductivity in SRO thin-films prepared by pulse laser deposition (PLD) [4,5] and several groups by molecular beam epitaxy (MBE) [6,7]. However, in all reports the growth parameter space for achieving superconductivity is narrow and although high purity is essential, the key underlying microstructural defects that suppress superconductivity remain unknown. In this talk we report the systematic growth of superconducting SRO thin-films by PLD from a Ru-rich SRO single crystal target and correlate suppression of superconductivity to in-plane (tilt and edge dislocations) and out-of-plane (inhomogeneous strain) structural defects. The results offer a breakthrough in understanding and enable the reliable, routine, growth of SRO thin-films. [1] Maeno, Y.et al. Evaluation of Spin-Triplet Superconductivity in Sr2RuO4. J. Phys. Soc. Japan 81, 1–29 (2012). [2] Mackenzie, A. P. et al. Extremely Strong Dependence of Superconductivity on Disorder in Sr2RuO4. Phyisical Rev. Lett. 80, 161–164 (1998). [3] Mao, Z. Q. Suppression of superconductivity in Sr2RuO4 caused by defects. Phys. Rev. B 60, 610–614 (1999). [4] Krockenberger, Y. et al. Growth of superconducting Sr2RuO4 thin films. Appl. Phys. Lett. 97, 082502 (2010). [5] Cao, J. et al. Enhanced localized superconductivity in Sr 2 RuO 4 thin fi lm by pulsed laser deposition. Supercond. Sci. Technol. 29, 1–6 (2016). [6] Uchida, M. et al. Molecular beam epitaxy growth of superconducting Sr2RuO4films. APL Mater. 5, 1–6 (2017). [7] Nair, H. P. et al. Demystifying the growth of superconducting Sr2RuO4 thin films. APL Mater. 6, (2018).

Resume : Functional oxides are a very interesting class of materials due to their singular characteristics comprising superconductivity, magnetism, ferroelectricity, catalytic activity, resistive switching or electro-optic effects, among others [1]. Yttria-Stabilized Zirconia’s (YSZ) structural and optical properties include thermal and chemical stability; a refractive index of about 2.14, a large optical energy bandgap (~5 eV) that prevents two photon absorption (TPA) in the near and mid-IR; transparency from visible to mid-IR and a good Kerr effect. Moreover, it has also been reported as an interesting material to be combined with either silicon or other platforms including sapphire, providing an effective buffer layer for other epitaxial functional oxides [2]. By means of material engineering, manipulation of these properties to build active reconfigurable elements in complex systems will lead to new functionalities including on-chip optical amplifiers that may be instrumental for a large number of nanophotonics applications. We recently demonstrated YSZ waveguides with propagation losses as low as 2 dB/cm in telecom wavelength range [3]. Based on these encouraging preliminary results, we have recently explored the possibility to introduce active rare-earth dopants into YSZ to demonstrate on-chip optical waveguides amplifiers based on YSZ. Yttrium-to-erbium substitution can be performed in the YSZ crystal, enabling a nearly perfect allocation of Er ions in the host matrix. For this purpose, we have studied structural and optical properties of Er3 ions in different platforms using a multilayer approach and deposited by Pulsed Laser Deposition (PLD) technique. We prove outstanding luminescence around λ = 1.54 µm, in correspondence with the C-band of telecommunications and in the visible range under a continuous-wave pump laser excitation at about 980 nm and 1480 nm. At the shadow of those results, we explored light amplification of Er-doped thin layers deposited on a SiN passive photonic platform. [1]. Lorenz, M., et al. Journal of Physics D: Applied Physics, 49, 433001 (2016). [2]. Jun, S., et al. Appl. Phys. Lett. 78, 2542 (2001). [3]. Marcaud, G., et al. Rev. Phys. Materials 2, 035202 (2018).

Resume : Ferroelectric (FE) materials are under intense scrutiny for photovoltaic applications (PV), following the demonstration of above 8% conversion efficiency in FE-based solar cells [1]. In these cells, there is no need for a p-n junction because the electric polarization from ferroelectricity is responsible for the current flow. The key issue for the development of oxide absorbers for PV is their bandgap that is generally above 3 eV. In this work, we produced Bi2FeCrO6 (BFCO) oxide materials by pulsed laser deposition (PLD). The structural, optical and electrical properties are presented. High quality epitaxial growth and phase-pure films are demonstrated by X-ray diffraction. We have studied the evolution of parameters such as the bandgap versus the growth conditions, proving that it can be adjusted from 1.9 to 2.6 eV [2]. Resonant X-ray diffraction is performed at ESRF to investigate the origin of the variation of the bandgap. The ferroelectric properties are investigated by piezoresponse force microscopy (PFM). We observe that light influences the state of polarization of BFCO. Finally, devices based on BFCO are fabricated and their photovoltaic properties are analysed. References: [1] R. Nechache, C. Harnagea, S. Li, L. Cardenas, W. Huang, J. Chakrabartty, F. Rosei, Nature Photonics, 2015, 9, 61 [2] A. Quattropani, D. Stoeffler, T. Fix, G. Schmerber, M. Lenertz, G. Versini, J. L. Rehspringer, A. Slaoui, A. Dinia and S. Colis, Journal of Physical Chemistry C 122, 1070 (2018)

Resume : Oxide thin films continue to attract paramount attention due to the broad range of properties they exhibit for applications. This presentation gives a short review on oxide thin films grown by pulsed electron beam deposition technique (PED) with focus on the correlation between composition, structure and physical properties. We will consider examples of epitaxial undoped and doped oxide thin films that are obtained by PED starting from relatively low substrate temperatures. The tuning of their physical properties is obtained due to the precise control of the growth conditions. In fact, changes in substrate temperature, working gas or pressure lead to strong effects on the optical transparency and/or electrical conductivity. These effects will be discussed in relation with the film composition, evidencing the role played by the dopant and/or oxygen on the oxide film properties. It is therefore possible to obtain by PED either stoichiometric oxide films or oxygen deficient metastable phases. These significant changes lead to pure or nanocomposite oxide thin films with specific characteristics and properties for applications.

Resume : We have developed a high-throughput method to explore how surfaces of polycrystalline ceramics impact phase formation and epitaxial orientation relationships during thin film growth. Instead of using a single crystal substrates, the combinatorial substrate epitaxy (CSE) involves film deposition on polished surfaces of polycrystals and determination of local epitaxy using electron back-scatter diffraction. After a review of prior observations, our recent work on the development of new electronic materials using CSE will be presented. In each case, targeted new electronic materials will be described along with efforts to stabilize them by CSE. Here, the discussion will include the following composition: BiFeO3, Ca2Mn4 or Dy2Ti2O7. These results further demonstrate the potential of CSE in the design and growth of a wide range of complex functional oxides.

Resume : The sputter deposition of (poly-)crystalline binary oxides seems allegedly simple. However, this is not entirely true, since there exist binaries which as crystalline material only exhibit one stoichiometry and one crystal structure, those which possess different polytypes at one distinct stoichiometry and those which feature crystalline phases at different stoichiometries. The material’s properties and the material’s phase obtained will strongly depend on the synthesis parameters, e.g., gas fluxes, substrate temperature, substrate, etc. Thus, in case of binary systems exhibiting various crystalline phases, changing these parameters allows one to establish phase maps in dependence on the growth parameters. Furthermore, combining several sputter sources in order to perform combinatorial screening of thin film materials allows an additional fine-tuning of the material’s properties and enables the buildup of materials libraries. Such high-throughput screening is also of major economic importance as designed functional materials are behind future key technologies and play an essential role in their evolution. Moreover, buffer layers deposited on the substrate surface prior to the preparation of the actual functional layer might increase the quality of the growth of the functional layer itself or provide a surface triggering a preferential crystal orientation. We present the capabilities of ion-beam bombardment for thin-film processing, especially for deposition of thin films by ion-beam sputtering. Different arrangements of ion sources, targets, and samples are discussed in general terms and the versatileness of ion-beam techniques in the synthesis of thin films and multilayer structures is highlighted by giving several examples on metal oxides: Ion-beam sputtering (IBS) of various binary oxides as well as combinatorial growth of materials libraries of ternary metal oxide systems and highly controlled buffer layer growth.

Resume : Recently efforts on the growth of magnetic metallic thin films on functional ferroelectric oxides have allowed manipulating magnetism via electric fields, so-called magnetoelectric (ME) coupling, which is attractive for energy-efficient memory device applications. Multiferroic heterostructures, such as Fe/BaTiO3 and Fe/0.7PbMg1/3Nb2/3O3-0.3PbTiO3 (PMN-PT), rely on the large interfacial strain and charge co-mediated ME coupling between the piezoelectric and charge effects in the ferroelectric oxide layer and the magnetostriction in the adjacent ferromagnetic layer. Understanding the contribution of the various interface mechanisms to the detected ME coupling is a challenge in the field of multiferroic heterostructures. In this work, Fe thin films are grown on PMN-PT single-crystal substrates using molecular-beam epitaxy. To discriminate between the various interface effects contributing to the ME coupling, we have developed a new approach in local and quantitative Mössbauer characterization of electric and magnetic field profiles. To this end, the magnetic Fe constituent is enriched with 57Fe probe layers either at or further away from the metal/oxide interface, which enables probing the oxidation state, lattice distortion, and magnetism with sub-nm resolution. The efficiency and flexibility of this technique have been previously demonstrated for Fe/BaTiO3 and Fe/LiNbO3.1,2 [1] S. Couet, et al., Adv. Fun. Mater. 24, 71 (2014) [2] M. Bisht, et al., Adv. Mat. Interfaces 3, 1500433 (2016)

Resume : In this work, NaNbO3 (NN) thin films were grown on the TiN/SiO2/Si substrate using pulsed laser deposition (PLD) system to realize memristor having synaptic plasticity and meta-plasticity. The NN thin films grown at low temperatures (300oC) exhibited the amorphous phase. The NN thin films exhibited a bipolar resistive switching behavior and it can be explained by the formation and rupture of the oxygen vacancy filaments. This NN films showed the excellent retention properties (> 104 sec) and the reliable endurance properties (> 400 cycles) with a low power consumption. Moreover, the synaptic properties such as spike-timing-dependent-plasticity (STDP), short-term-plasticity (STP), long-term-plasticity (LTP) and spike-rate-dependent-plasticity (SRDP) of the NN ReRAM devices were also obtained in the NN film. The meta-plasticity of biological synapses was also implemented in the NN memristor, including the metaplasticity of STDP. Therefore, the NN memristor could be used as an artificial synapse in neuromorphic computing system.

Resume : In filamentary resistive random access memory (RRAM) devices, the resistance state of the device is changed via formation and annihilation of a conductive filament within the device switching layer (usually an oxide layer). The mechanism responsible for forming this conductive filament is highly dependent of the type of atoms or anions that drift under the applied external bias during the switching process. In extrinsic switching devices, drifted metallic cations from the device electrochemically active top electrode coalesce and form a metallic filament. On the other hand, oxygen vacancies generated by the movement of oxygen anions consolidate to form the conductive filament in intrinsic switching devices. Here, we show that the two mechanisms, and their associated filaments, can coexist in SiOx RRAM devices with Ag top electrodes. This multifilament formation process happens during the device cycling. The nature of the formed filament and its corresponding switching mechanism were probed using resistance vs temperature measurements. The order in which the two mechanisms are initiated is dependent on the polarity of the applied external bias during electroforming and subsequent switching. We will also discuss how to separate the two mechanisms by controlling the oxygen environment of the device during switching.

Resume : The ability to combine standard wafer-scale semiconductor processing with the excellent properties of functional oxides opens the possibility to realize innovative and more efficient devices with high value applications that can be produced at large scale. However, the precise control of interfaces and crystallization mechanisms of dissimilar materials rest extremely challenging. As an example, the scalable and sustainable integration of high quality epitaxial oxide nanostructured thin films on silicon need to be further developed. In this regard, I will present successful strategies that integrate functional oxides nanostructures on silicon via chemical solution deposition (CSD) approach. Divers examples will be presented separated in two different approaches i.e.: (i) perovskite oxides with enhanced physical properties by combining physical and chemical methods, such as epitaxial nanostructured BiFeO3, BaTiO3 or La0.7Sr0.3MnO3 thin films on silicon [1-3], and (ii) oxide nanomaterials entirely performed by soft chemistry and scalable top down lithographic techniques, such as nanostructured piezoelectric quartz thin films on silicon [4] or novel 1D-ferroelectric complex oxide epitaxially grown on silicon for vibration energy harvesting. The methodologies presented here exhibit a great potential and offers a pathway to design novel oxide compounds on silicon substrates by chemical routes with unique optical, electric, or magnetic properties. All these works have received funding from the European Research Council (ERC) and EU-H2020 research and innovation program under grants agreements No 803004 (SENSiSOFT) and No 654360 having benefitted from the framework of the NFFA-Europe that will be shortly presented after this talk. [1] Epitaxial La0.7Sr0.3MnO3 thin films on silicon with excellent magnetic and electric properties by combining physical and chemical methods. J. Vila-Fungueiriño et al. Science and Technology of Advanced Materials, Volume 19, (2018) [2] Electric and Mechanical Switching of Ferroelectric and Resistive States in Semiconducting BaTiO3–δ Films on Silicon. A. Gómez, J. et al. Small, 1701614 (2017) [3] Integration of functional complex oxide nanomaterials on silicon. J. Vila-Fungueiriño et al. Frontiers in Physics 3, 38 (2015) [4] Soft chemistry based routes to epitaxial α-quartz thin films on silicon with tunable textures. A.Carretero-Genevrier et al. Science. Vol 340. Pp 827-831 (2013)

Resume : Optoelectronic devices are mainly based on different semiconducting materials, which combination generates the presence of internal electric fields that can be used to drive carriers generated by light. Thus optical stimuli results in a change of the device electric properties. In ferroelectric materials, ferroelectric parameters such as polarization and coercive electric field are known to be modified under appropriate illumination. However, these changes do not present any advantage in front of the semiconducting based optoelectronic devices. However, if one could control the ferroelectric parameters by light in a non-volatile manner, the resulting device would present the advantage of having memory. In our contribution, we will demonstrate that by the control of surface adsorbates related to water in BaTiO3 films, we can switch on and off a particular ferroelectric property [1]. In this realization, we obtain a non-volatile modification of the measured switchable ferroelectric polarization under illumination, which persists when illumination is suppressed. X-ray photoelectron spectroscopy (XPS) experiments performed under visible light illumination have allowed to elucidate the origin of this phenomenon in the characterized BaTiO3 films, which will described in detail in our contribution. [1] F. Liu, I. Fina, G. Sauthier, F. Sanchez, A.M. Rappe, J. Fontcuberta, ACS Appl. Mater. Interfaces 10, 23968 (2018)

Resume : The recent advances in the study of ferroelectric nanodomains has stimulated intense research in order to contribute to the fundamental knowledge of ferroelectric materials as well as for applications. Superlattice geometry provides a means to investigate domains at the nanoscale: by alternating individual ferroelectric layers with dielectric layers, it is possible (1) to produce ferroelectric domains which are isolated from surface or film-substrate interfaces, (2) to modify the electrostatic boundaries and mechanical strains., and (3) to tune the functional properties of the superlattices by adjusting the ferroelectric/ dielectric layer ratio. Here we present experimental results on a series of Pb(Zr0.2Ti0.8)O3 /SrTiO3 superlattices in which we evidence 180° stripe polar nanodomains. The structural and microstructural characteristics of these superlattices will be presented and the influence of the multidomain state on the ferroelectric phase transitions and the temperature dependant dielectric response will be reported.

Resume : Multiferroic materials, by combining ferromagnetism to ferroelectricity, are a promising playground for novel information storage devices. In particular, they could allow for the control of magnetization by an electric field or the control of electric polarization by a magnetic field. In this perspective, we have studied two-phase multiferroic heterostructures consisting of La0.7Sr0.3MnO3 (LSMO) and BaTiO3 (BTO) layers, with a thickness of about 50 nm, deposited by pulsed laser deposition (PLD). The LSMO and BTO layers may be grown epitaxial on MgO(001) with a cube-on-cube relationship. We made the Au/BTO/LSMO junction by means of lithography. Firstly, results will be presented, related to the crystalline atomic structure of the BTO/LSMO junction which was studied by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The atomic chemical composition was studied by Rutherford backscattering spectrometry (RBS) and electron microscopy derived techniques (EDX and EELS). Secondly, we will show that the LSMO layer provides ferromagnetic properties very close to the bulk ones, in particular a high value of the saturation magnetization (Ms about 150 kA.m-1 at 300 K), associated to a very small coercitive field (30 Oe at 300K), that means a possible low-field switch of the magnetization. In addition, the LSMO layer is metallic from 300 K up to 28 K. Finally, we will demonstrate the ferroelectric character of the junction, ensured by the BTO layer and checked through intensity-voltage (I-V) measurements by the use of top Au electrodes. A resistive switching behavior will be evidenced, explained on the basis of polarization switching. These results pave the way towards multiferroic tunnel junctions, with different resistive states according to the polarization state.

Resume : Multiferroic materials show a coupling of ferroelectricity, ferromagnetism and ferroelastisity leading to a wide range of multifunctional devices, such as memories, sensors, and microwave devices. Materials with strong piezoelectric Pb0.52Zr0.48TiO3 (PZT), dielectric BaTiO3 (BTO) and magnetostrictive properties, CoFe2O4 (CFO), have been intensively studied in multilayered multiferroics. However, the strain in the multilayers is limited due to a substrate-imposed clamping resulting in small ME coupling. In this work, we have developed new strategies for the preparation of (1-3) multiferroic nanocomposites consisting of vertically aligned nanopillars (1) embedded in a matrix (3). Two kinds of materials were considered: i) CFO nanopillar arrays embedded in a BTO matrix, where an original in situ oxidation of magnetic CoFe2 nanopillars was used during rf magnetron sputtering of BTO; ii) CFO nanopillar arrays embedded in a PZT matrix, where in the first experiment, magnetic CoFe2 nanopillars were thermally oxidized, followed by the impregnation of the PZT using a sol-gel technique.1-3 The magnetoelectric coupling in the CFO nanopillar arrays embedded into BTO and PZT matrices can be interpreted by piezoelectricity and magnetostriction of the two phases, along with the reduced clamping, which enhances the strain interaction. [1] Sallagoity, et al., RCS Adv. 6, 106716 (2016) [2] Basov, et al., Nanotechnology 28, 475707 (2017) [3] Elissalde, et al., Ferroelectrics 532, 138 (2018)

Resume : The ferroelectric (FE) behavior of thin doped hafnium oxide films or hafnium zirconium mixed oxide layers caused by a non-centrosymmetric orthorhombic phase was reported recently. Novel devices ranging from FE RAM (random access memory) and FE FET (field effect transistor) to ferroelectric tunnel junctions and negative capacitance devices using these dielectrics were proposed. For all devices a detailed understanding of the structural properties is necessary to improve the electrical performance of the material stack. Ferroelectric doped HfO2 films are typically processed by atomic layer deposition (ALD) or physical vapor deposition (PVD), but other deposition techniques like pulsed laser or molecular beam deposition are possible too. Depending on the deposition technique, process parameters like oxidant flow (e.g. PVD) or pulse time (ALD) during deposition can impact the ferroelectric properties of HfO2. In addition, the oxidant itself (H2O, O3, O2 plasma) determines oxygen, defect and contamination concentrations for ALD deposited films that can have an influence on the primary phase of HfO2. Furthermore, dopants, stress and grain size play a significant role in the phase formation process during crystallization. Overall, the impact of these process parameters on the ferroelectric devices performance is identified.

Resume : The experimental confirmation of ferroelectricity in thin films of the Hf1-xZrxO2 system has been clearly established (Appl. Phys. Lett. 110, 182905). However, a complete theoretical understanding of this behavior is still needed. The differences in the properties of films as a function of x for the same preparation conditions (Nano Lett. 12, 4318) invites exploration of the role played by cations ordering at the atomic level. In order to clarify this, we focus here on thin films with x=0.5 prepared by atomic layer deposition following different Hf/Zr sequences. 10-nm thick polycrystalline layers with overall Hf0.5Zr0.5O2 composition were deposited at 200ºC on TiN/SiO2/Si substrates using TDMAH and TDMAZ precursors. After deposition of TiN top electrodes the films were annealed in N2 atmosphere at moderate temperature which was high enough to induce the crystallization but low enough to prevent significant cation intermixing. The orthorhombic crystal structure was confirmed by X-ray diffraction. The film microstructure at the sub-nanometric level including Hf/Zr ordering was studied by transmission electron microscopy and electron energy loss spectroscopy. In the presentation we will show the correlation between the structure and ferroelectric properties of the films, as well as the influence of the cation disorder in this behavior. The conclusions enable a better understanding of the unusual ferroelectric properties of these simple binary oxides.

Resume : Recently discovered, doped HfO2 [1] is a promising candidate for several ferroelectric applications. Among them, the most addressed are Negative-Capacitance Field Effect Transistor (NC-FET) and Ferroelectric Random Access Memory (FRAM). Compared to other materials, HfO2 processes have not only the advantage of being already integrated in Si CMOS industry, but also its ferroelectric properties are adequate for using oxide layer thinner than 10nm. Nevertheless, some of its properties should be improved for industrial applications. During cycling, the main issues are the limitation of the wake-up effect and the imprint, the fatigue and the endurance of the material. The ferroelectric phase (f-phase) has often been studied by Atomic Layer Deposition (ALD) [2]. However, most of the time the electrodes are made by Physical Vapor Deposition (PVD) processes, and industrial processes to separate Hf and Zr are usually expensive. It could be interesting to have only one process where the separation of Hf and Zr is not needed and where all depositions are made in the same machine. Furthermore, one of the most important benefit of sputtering is the deposition time which can be until 120 times faster than ALD depositions for the oxide layer. In this presentation, details will be given on how we succeeded in the deposition of ferroelectric hafnium/zirconium oxide (HZO) solid solutions by changing the pressure in the magnetron sputtering chamber in order to realize Metal/Insulator/Metal (MIM) capacitors. X-rays Diffraction (XRD), Transmission Electron Microscopy (TEM) and advanced electrical characterizations have been led to understand the difference between ferroelectric and non-ferroelectric samples. Two targets will be compared: a metallic Hf/Zr (56/44) target (reactive sputtering) and an oxide ZrO2/HfO2 (50/50) target (non-reactive sputtering). On these two targets, stoichiometry issues will be described and different fabrication tests have been led, such as: annealing at different temperatures, changing the size of the ferroelectric insulator layer, changing the size and the materials of the bottom and top electrodes, changing the oxygen flows, annealing with and without top electrodes. In each one of the studies, our understanding of the phenomena involved will be given. References: [1] T.S. Böscke, J. Müller, D. Bräuhaus, U. Schröder, U. Böttger, Ferroelectricity in hafnium oxide thin films, Appl. Phys. Lett. (2011). [2] M.H. Park, Y.H. Lee, H.J. Kim, Y.J. Kim, T. Moon, K. Do Kim, J. Müller, A. Kersch, U. Schroeder, T. Mikolajick, C.S. Hwang, Ferroelectricity and Antiferroelectricity of Doped Thin HfO2-Based Films, Adv. Mater. (2015)

Resume : Hafnium oxide is pivotal in CMOS related applications and is being much investigated for data storage in resistive switching devices. The report of ferroelectricity in polycrystalline metal-doped hafnia samples opened new perspectives that have been further inflated by recent achievements showing that the ferroelectric phase can also be stabilized in epitaxial thin films. Here we report resistive switching observed in ultra thin ferroelectric films of Hf0.5Zr0.5O2. Films (about 4nm thick) grown by PLD on STO(001) substrates using (LaSr)MnO3 (LSMO) as bottom electrode. Two different type of metals (Pt and Co) have been used as top electrodes. We record the electroresistance (ER) by polarizing the junctions with different writing voltages. The junction resistance is measured through an current - writing voltage loop in small voltage range. Preliminary polarization loops have been recorded. It turns out that the device displays a remarkable polarization (about 15 uC/cm2) when measured at frequency 5 kHz with coercive voltage around 1.5 V. However when ER is measured in LSMO/HZO/Pt capacitors using a voltage-writing pulse of similar amplitude (?2 V) and duration, no ER is observed. In contrast, a large ER (900%) is observed for larger writing pulses larger, around 4-5V. In LSMO/HZO/Co capacitors, ER is still not observed for writing amplitude close to the coercive voltage but only larger. We conclude that ER is governed by ionic-motion modulated junctions rather than polarization.

Resume : The ferro-electric (FE) controlled “Mott transistor” shows great potential for non-volatile low power electronics. However, the achievement of the optimal field effect in the heterostructure is still challenging and its origin is not well understood, which hinder the practical device applications and development. [1-3] We investigate the field effect mechanism in a T-BiFeO3/(Ce,Ca)MnO3 (T-BFO/CCMO) bilayer Mott transistor using PFM ex-situ poling and Cs-corrected STEM and EELS spectro-microscopy. For a ferro-electric gate layer thicker than 10nm, an incomplete FE switch occurs. Only ca. 20% of BFO at the interfaces with the channel is successfully switched which is below the percolation threshold and explain the great deterioration of the resistance switch for theses devices. Such FE domain distribution result in the formation of tail-to-tail domain walls along (001) and {011} planes. The DW have widths of a typically 3-6 u.c. and present some structural disorder but no charge (Fe4 ) were evidence by EELS. Screening effect in the BFO imply a combination of defect, BFO surface charge and CCMO interface charge. Furthermore, when the switching is successful, a large modulation of ca. 2.4e- is found in the CCMO channel between the accumulation and depletion state, which is comparable to the values expected from an electrostatic value and confirm the potential of T-BFO gating to manipulate large amount of charge. [4] 1 Yamada H. et al. Scientific Reports 3, (2013). 2 Boyn S. et al. APL Materials 3, 061101 (2015) 3 Marinova M. et al. Nano Letters 15, 2533-2541, (2015). 4 Li X. et al. in preparation (2019).

Resume : The investigation of lattice vibrations in multiferroic BiFeO3 (BFO) crystals and thin films is of relevance for various practical applications due to their correlation to structural properties. However, the assignment of phonon symmetry is still controversial in the literature, due to the polar character of the oblique modes. Here we present symmetry assignment of the phonons obtained using azimuthal rotation dependent Raman measurements together with simulations based on Raman tensor formalism as well as taking into account mixed symmetries for the polar modes.[1] Raman spectroscopy can be used as a powerful tool for the investigation of ferroelastic domains in BFO exploiting the strong anisotropic intensity variation of some of the polar modes. Raman line scans and mappings were employed in order to identify ferroelastic domain patterns. Moreover, line scans performed with different excitation wavelengths and hence different penetration depths give information about the tilt of the domain walls with respect to the sample surface. Further, we will exemplify how Raman spectroscopy can be used as a tool to probe phase transitions such as orbital ordering in the case of 3d transition metal oxides. [2] The orbital ordering transition for LaVO3 and PrVO3 epitaxial films deposited on different substrates is addressed. [1] C. Himcinschi et al., Sci. Reports (2019) (in print, DOI: 10.1038/s41598-018-36462-5) [2] I. Vrejoiu, C. Himcinschi et al., APL Mater. 4, 046103 (2016).

Resume : Piezoelectric thin films for microsystems have recently met some noticeable industrial success such as AlN for acoustic RF filters and Pb(Zr,Ti)O¬3¬ (PZT) for inkjet print-heads actuators. In the case of perovskite oxides such as PZT, the sol gel technique has become the standard deposition means thanks to the high quality of the grown films on silicon. This approach gives nowadays the opportunity to think of deposition techniques that are more versatile such as inkjet printing (IJP). This leads to low cost and reliable fabrication techniques with which neither lithography nor etching are required anymore. Moreover, one can think of printing piezoelectric thin films on alternative substrates such as steel, glass or even polymers. At LIST, we study Chemical Solution Deposition (CSD) for functional oxides and more specifically for piezoelectric films. In this talk, I will present our latest advances regarding CSD and IJP deposition of piezoelectric films on silicon and glass substrates [Godard et al., Adv. Mat.Technol, 1800168 (2018)]. The key parameters of CSD and IJP will be discussed together with a comparison of the piezoelectric properties films on silicon and glass. Finally, two applications will be detailed, namely 1) an all-printed energy harvester and 2) fully transparent ultrasonic transducers, embedding transparent electrodes.

Resume : Epitaxial PbZr0.2Ti0.8O3 capacitors were manufactured on single crystal SrTiO3 substrates with bottom and top SrRuO3 electrodes. Electrical measurements, namely polarization-voltage (P-V or hysteresis) and capacitance-voltage (C-V), were performed to evidence ferroelectricity. A modified C-V measurements was also developed to obtain the capacitance value in static conditions, with pre-set polarization state. The main conclusions of this study are: the experimental P-V and C-V characteristics are not in agreement with the theory predicting that the second is the derivative of the first one; the static C-V measurements reveal the fact that, after polarization switching and saturation, the capacitance value is practically constant, with negligible dependence on the applied voltage; the capacitance value calculated from static C-V at different thicknesses of the PZT layer extrapolates towards optical dielectric constant at thickness limit for stable ferroelectricity (about 1.2 nm); the derivative of P-V loop reveal the presence of a negative capacitance effect in the voltage range around coercive voltage, thus around zero value of polarization. It is suggested that, in almost perfect epitaxial PZT films, as it is the case for very thin films, the volume is completely depleted of free carriers, all being attracted to the electrode interfaces to compensate polarization charges. This may explain the low value of dielectric constant and the negative capacitance effect around P=0.

Resume : Thin films of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) have been shown to exhibit attractive properties, which can be exploited for energy harvesting (EH), energy storage and electrocalorics. While most of the research and applications of thin-film piezoelectric EHs are based on the d31 mode, the d33 mode offers a higher potential figure of merit. We found that PMN-PT grown directly on SrTiO3 (STO) is extremely sensitive to the deposition conditions, easily leading to the nucleation of the undesired Pb-deficient pyrochlore phase. Contrarily, the window for growing phase-pure PMN-PT on STO, covered with a LaNiO3 bottom electrode, is considerably broader. In order to find the origin of the phase stabilization, we grew PMN-PT on other buffer layers such as SrO, SrRuO3 and PbZr0.52Ti0.48. The main reason for the enhanced stability of the perovskite phase was found to be the increased interface roughness, which enables stronger binding of Pb-based species. Thus, we modified the surface of the STO substrates by depositing a homoepitaxial layer prepared with a specifically designed process that ensures the growth of a stoichiometric and simultaneously rough STO layer. This led to a significantly improved phase purity of PMN-PT on STO, which represents an important step in the fabrication of EHs that operate in the d33 mode. Additionally, applying the same principle, other rough buffer layers can be designed to improve the integration of different Pb-based functional oxides on Si.

Resume : The perovskite KxNa1-xNbO3 lead-free material is ever more investigated for its promising piezoelectric and ferroelectric properties. In the same K-Na-Nb-O (KNN) system, a tetragonal tungsten bronze (TTB) phase was reported but never fully investigated until now. This type of structure is known to exhibit piezoelectric properties in other systems such as Li-Na-Nb-O chemically close to KNN. However the synthesis and the identification of pure TTB phase are sensitive due to growth competition with numerous phases in these chemical systems. Therefore, the growth conditions using the pulsed laser deposition were optimized to obtain pure TTB KNN thin films. To identify the TTB phase with certitude, X-ray diffraction and electron transmission microscopy with electron diffraction techniques have been used. Raman spectroscopy as well as Energy Dispersion X-ray Spectroscopy and Scanning Electron Microscopy were also carried out to properly characterize the thin films. Pure TTB thin films have been deposited on (100) and (110) SrTiO3 substrates in order to investigate the oriented growth of the distinctive TTB nanorods. The low frequency (1 kHz - 1 MHz) dielectric characteristics (permittivity and loss tangent) have been retrieved from a thin film grown on (111)Pt/(001)Si substrate, whereas a thin film on C-cut sapphire substrate was used for measurements and characterizations at microwaves (1GHz - 40 GHz). A quite high dielectric permittivity value between 80 and 150 was measured.

Resume : Research on novel lead-free pyroelectric thin films is triggered by their promising integrability in CMOS processes and application in environmental friendly infra-red sensors. High precision characterization of such materials is a key challenge in development of new lead-free pyroelectric materials. In this study, we report on the characterization of pyroelectric thin films and piezo-composites, in particular analysis of the pyroelectric response and micro- and nanoscale thermal analysis, by using an advanced laser-based stimulation technique. We identified wide band gap semiconductor thin films fabricated by PVD and CSD processes, including Aluminum nitride and Scandium doped Aluminum nitride, as model materials for pyroelectric sensors due to their excellent dielectric properties and CMOS compatibility. By high frequency stimulation of a quantum cascade infrared-laser with selectable wavelength we measured through thickness polarization and thermal flux of exposed and integrated samples similar to the Laser Intensity Modulation Method. Parasitic piezoelectric contributions are accounted and modeled. These results are complemented by thermal simulation, and microscopic and spectroscopic techniques for fundamental thermal analysis down to the nanoscale. Our novel laser-based measurement system is an essential step forward for precise material characterization in research, and quality control on industrial scales for optimized device reliability.

Resume : The study of II-VI semiconductor has attracted much attention due to their potential applications in several fields. They are excellent candidates for optoelectronic devices due to their large direct band gap, chemical stability and large exciton binding energy. Among the II-VI semiconductors, ZnO is the most studied and applied in the fabrication of devices. The doping of ZnO with Yttrium has extended its use in gas sensors, solar cells or LEDs, as this dopant improves the optical and electrical properties of the zinc oxide. In this work, the material has been studied in two cases. Y-doped ZnO ceramics have been sintered, using a mixture of ZnO or ZnS and Y2O3 as precursor. Besides, doped micro and nanostructures have been grown using a vapor-solid method, using ZnS and Y2O3 as precursor. In both cases, the starting Yttrium content ranges from 0.4 to 3.6 at.%. Different characterization techniques have been applied to understand the differences between the ceramics and nanostructures properties. The characterization of the Y-doped ZnO has been performed by scanning electron microscopy based techniques: emissive mode, cathodoluminescence (CL) and X-ray microanalysis. Also, micro-Raman and X-Ray Diffraction measurements have been made. Special attention has been focused on the influence of the dopant in the CL emission and in the morphology of the micro- and nanostructures grown. As a proof of concepts, the behaviour as a gas sensor of the treated material have been studied.

Resume : Due to biocompatibility, chemical stability, non-toxicity, abundance and simple manufacturing process, metal-oxides are attractive materials to fabricate nanostructured optoelectronic devices, like photodetectors or solar cells. Nanowire (NW) based solar cells have been demonstrated to possess advantages in terms of electrical and optical properties over traditional thin film devices. Nowadays, resolving functional properties with high spatial resolution is crucial for future generation energy harvesting systems made up of heterogeneous nanoscale features. Atomic force microscopy (AFM) is a characterization method which allows to obtain functional imaging of surfaces, beyond morphological information with a resolution in the range of the nm. Conductive-AFM (c-AFM) is a powerful technique to obtain nano-electrical characterization related to the morphology of the surface. In this work, hydrothermally grown NWs of n-type oxides (ZnO and TiO2) have been conformally covered by p-type oxides (Cu2O and Co3O4) by different deposition methods, like ALD, CVD and sputtering. We successfully obtained core-shell ZnO-Cu2O and TiO2-Co3O4 NWs, which exhibit good photodetection (with a fast response time <0.1 s) and photovoltaics performances (achieving VOC = 0.34 V, JSC = 50 μA/cm2 and FF = 45%, in the macroscopic J-V characteristic). C-AFM measurements in dark and under illumination allowed to obtain the local photo-electrical properties of the investigated oxide materials at the nanoscale.

Resume : Recently, implantable bio-electronic devices have attracted considerable attention owing to their promising potentials in monitoring and regulating malfunctioned neural systems and internal organs. In operation, these devices require a bio-compatible interface to facilitate the electrical signal communication between inorganic Si-based circuits and neurons/cells in an aqueous environment. A critical parameter for a bio-electrode is its “charge storage capacity” (CSC). A larger CSC is desirable for electrode miniaturization and irreversible-reaction minimization. We develop a chemical bath for a conformal iridium oxide deposition with a thickness of ~15 nm on titania nanotubes with length of ~800 nm. In addition, we develop an anodization process which can control the spacing of titania nanotube array. These IrO2 nanotube arrays undergo electrochemical analysis in charge storage capacity (CSC) and electrochemical impedance to evaluate its potential as neurostimulating electrodes for bioelectronics. Images from electron microscopes confirm the formation of uniform IrO2 on both internal and external surface of nanotubes. An X-ray diffraction pattern indicates a good crystallinity of the IrO2 nanotube array. In addition, the cycling lifetime of IrO2 nanotube arrays is evaluated by performing CV scans for 1,000 cycles with a scan rate of 0.1 V/s. The IrO2 nanotube arrays reveal large CSC values and low electrochemical impedances which are attributed to hollow tubular nanostructure with IrO2 deposition. Additionally, the IrO2-coated titania nanotube array exhibits stability, durability, and good biocompatibility.

Resume : Nowadays thin film transistors (TFTs) are widely applied in flat panel displays, including active-matrix liquid-crystal displays. In order to achieve a higher resolution it is required to increase the pixel density and, thus, the TFT density implemented in the panel. Under these circumstances, the commonly used a-Si:H TFTs need to be replaced by alternative materials with larger electron mobilities. In this context, we want to introduce a new ZnMgON-based material to improve the TFT’s performance. This alloy can be considered as a combination of the four binary compounds ZnO, MgO, Zn3N2 and Mg3N2. Due to the numerous physical differences between these binaries including crystal structure, lattice parameters and coordination numbers, the stabilization of this new material requires growth methods far from equilibrium, such as molecular beam epitaxy (MBE), and crystalline substrates of wisely-chosen symmetry imposing a certain crystal structure to the desired alloy. In this contribution we present the growth of the above-mentioned binary thin films and first ternary alloys by MBE as a first step to achieve ZnMgON layers. The structural and surface properties were analyzed by X-ray diffraction and atomic force microscopy, respectively while X-ray photoelectron spectroscopy has been used to qualify the film composition. Finally, preliminary results on optical characterization will be shown and compared with those of nanopowders commonly used in ceramic industry. ANR-17-CE24-0043-01

Resume : The alkali-earth oxide phosphor SrO:Bi offers a potential low-cost alternative to lanthanide-based blue phosphors. It has been reported in the powder form due to its properties and applicability in several types of optoelectronic devices. Pulsed laser deposition (PLD) was used to grow thin films from a Sr1-xO:Bix=0.002 target prepared from powders optimized for blue luminescence and obtained by sol-gel combustion. Thin films were successfully fabricated by PLD in vacuum or an O2 working atmosphere on Si (100) substrates. Films were deposited at different substrate temperatures using a Nd:YAG laser (266 nm) with energy 33.3 mJ/pulse, a KrF laser (248 nm) with energy 300 mJ/pulse or an ArF laser (193 nm) with energy 150 mJ/pulse. The X-ray diffraction (XRD) of the films deposited using the Nd:YAG laser in O2 showed that the crystallinity increased with an increase in the substrate temperature, changing from amorphous to a cubic structure. All films deposited in vacuum were amorphous. The optimum substrate temperatures for the maximum luminescence (both photoluminescence (PL) and cathodoluminescence (CL)) were 200 °C and 50 °C for deposition in O2 and vacuum, respectively. The main PL emission peak position of the thin films showed a shift to shorter wavelengths at 427 nm, when compared to the powder (445 nm). The difference in wavelength was attributed to the Bi3+ ions, which are very sensitive towards the environment. XRD of the thin films obtained with the different types of excimer lasers showed the thin films also had a strong (111) preferential orientation on the cubic phase. PL spectra showed blue emissions at 425 nm with a small shift to shorter wavelength compared with the powder, which was attributed to Si diffusion in the films.

Resume : 0.92Bi0.5Na0.5TiO3 – 0.08BaTiO3 (BNT-BT) ferroelectric thin films have been grown on MgO(100) and Ir-coated MgO(100) substrates by using sol-gel method. The solution was prepared from bismuth acetate, sodium acetate anhydrous, titanium isopropoxide and barium acetate. An excess of 10 mol. % and 5 mol. % for the sodium and the bismuth, respectively, was used to compensate their evaporation during the crystallization treatment at 800 oC. Structural, and morphological characterization of the BNT-BT films were performed by X-ray Diffraction and Scanning Electron Microscopy. The dielectric properties were determined on out-of-plane metal-insulator-metal (MIM) and planar inter-digitated capacitors (IDC) microfabricated by photolithography. The characterization of the MIM and IDC structures was performed in the 100 MHz – 60 GHz frequency domain in reflection mode. The dielectric properties of BNT-BT thin films will be discussed with respect to their potential for integration in electrically controlled devices. Acknowledgements: This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CCCDI – UEFISCDI project number 61/2016 (MASTERS), within PNCDI III.

Resume : Lithium Tantalate (LiTaO3 or LTO) is a material with unique piezoelectric properties and high potential for application in Surface Acoustic Wave (SAW) filters. The combination of thin LTO layers with Si/SiO2 substrates allows the increase of SAW Q factors as well as the decrease of frequency temperature coefficient. One promising option to manufacture such structures is to transfer the LTO layer by using the Smart CutTM technology, which is based on Hydrogen ion implantation and annealing. How such a polar material reacts to H implantation is expected to be very complex. Also, the way its piezoelectric and structural properties are affected is not known. We studied the effect of H ions fluence (from 1e16 to 9e16 H /cm2) on strain generation within the implanted regions of initially single crystalline LTO (oriented off the piezoelectric axis [0001]). By combining high-resolution XRD measurements with elasticity theory we developed for this system, we extracted depth profiles of 3D full strain tensor components. Hydrogen depth profiles measured by SIMS and TEM cross-sectional imaging supported this investigation. We highlighted the appearance of strong shear strain in such modified regions and estimate strain-induced piezoelectric polarization distribution inside the layer. Finally, the relation between H concentration and strain will be discussed, as well as the impact of ion implantation on piezoelectric properties.

Resume : Cost-effective transparent conductive oxide (TCO) material composed of cheap and abundant elements is highly desired in today’s optoelectronics. Just recently wide-bandgap La-doped barium stannate (LBSO) semiconductor with outstanding electrical properties has been discovered. Synthesis of thin LBSO films is still challenging due to nonstoichiometry and various defects. Understanding of these factors is important for the control of the properties for application as transparent electrodes. Therefore, in this work Pulsed injection metalorganic chemical vapor deposition (PI-MOCVD) method was used for the growth of unmodified BaSnO3 (BSO) films. BSO films were deposited on LaAlO3, SrTiO3, sapphire substrates and film nonstoichiometry and defect issues were investigated. It was determined that a surplus amount of barium is required to obtain stoichiometric films. Also, slight deviation form stoichiometric ratio resulted in significant microstructure and optical properties changes whilst maintaining pure cubic phase. Increase of lattice parameter with the increase of Ba/Sn ratio in the films suggests a certain defect-forming mechanism possibly related to oxygen atom vacancies.

Resume : Transition metal oxides are characterized by a wide variety of magnetic, optical and catalytic properties that are now used in numerous electronic applications. Isostructural and isovalent iron and chromium oxides are the subject of active experimental and theoretical investigations last time. Up to now, Cr2O3 has been most promising material for realistic applications close to room temperature in magnetoelectric-controlled spintronic elements like MERAM. An important property of hematite is its low-toxicity, Earth abundant and suitable redox potential for photocatalytic water dissociation. Combination of these materials in multilayer composite can allow to obtain new multifunctional structure and leads to improve of their magnetic or optical properties. In our work, nanometric iron and chromium oxide layers, their multilayer combinations and solid solutions were grown on silicon and glass substrates by the reactive pulsed laser deposition techniques at various technological parameters such as oxygen pressure in the reactor, substrate temperature, number of laser pulses. The structural, electrical and optical properties of these films were then studied. The methods of low-temperature photoluminescence and Raman spectroscopy techniques, were used for the investigation of the recombination and vibrational properties. Study of the charge carriers’ transport kinetics was carried out by surface photovoltage (SPV) and impedance spectroscopy technique. It is shown that oxides are present on the surface in different phases, and the technological parameters and composition of these films significantly affect their properties.

Resume : The composition and microstructure of cathode materials has a large impact on the performance of solid oxide fuel cells (SOFCs). It was recently shown [1] that the sputter deposited (La0.8Sr0.2) CoO3 (LSC-113) - (La0.5Sr0.5)2CoO4 (LSC-214) dual phase cathode yield the best performance where the mixture had an amorphous-like structure. In this study a composite cathodes LSC113-LSC214 and LSF-LSM were synthesized via thermal plasma using a large flow rate of quenching gas yielding fine non-equilibrium cathode powder. The purpose is to see if similar performance improvement could be obtained with plasma synthesized composite powders. The powders were screen printed onto suitable electrolytes and were characterized based on EIS responses using a symmetric cell. [1] Sarı D. et al., Combinatorial Development of nanocrystalline/amorphous (La,Sr)CoO3-(La,Sr)2CoO4 Composite Cathodes for IT-SOFCs, Solid State Ionics, 326, 124-130, 2018. [2] Torunoğlu Z. Ç. et al., One pot synthesis of (La,Sr)CoO3/(La,Sr)2CoO4 for IT-SOFCs cathodes, Int, J. of Hydrogen Energy, 43, 18642-18649, 2018.

Resume : Thin iron oxide films were grown using the pulsed laser deposition (PLD) technique on quartz tubes at room temperature from a pure Fe target under various oxygen pressures. Two different laser sources (ArF, 193 nm and KrF, 248 nm wavelengths) were used. The structure of thin films were investigated using X-ray reflectivity and grazing incidence X-ray diffraction, while the chemical composition was investigated using X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface morphology was investigated using scanning electron microscopy. The deposited films were tested as chemo-electrical sensors in a home-made setup, against hexane and octane compounds, at various operating temperatures and vapor concentrations in air. The sensing properties of the iron oxide films were correlated with their growth parameters, and their structure, surface morphology and chemical composition.

Resume : BaTiO3 thin films (60 nm-thick) grown on SrTiO3/Si templates have been characterized for their structural and electrical properties. The epitaxy of the BTO film on silicon was confirmed by X-ray diffraction with a good crystallinity. The temperature-dependance structural properties were checked by infrared spectroscopy in the absorption mode. The films were found to remain in a single ferroelectric phase over a temperature range from 5 to 385 K. Low-temperature orthorhombic-rhombohedral phase transitions characteristic of bulk BaTiO3 are absent in the films due to the clamping effect from the Si substrate. The electrical characterizations of the BaTiO3 films using MFIS structures show that samples shows a memory window with hysteresis loops which thus enable BaTiO3 possibly being applied to the non-volatile memory application.

Resume : The properties of BaTiO3 (BTO) thin films deposited on different substrates by RF magnetron sputtering were investigated. Two representative substrates were selected and different heterostructures were studied. (i) SrTiO3 (STO) single crystals as a bulk oxide reference material, and (ii) silicon as a semiconductor. SrRuO3 (SRO) and Pt bottom electrodes were deposited on the silicon substrate. The BTO structural characterizations show that the films have (001) crystallographic orientation. We have compared the electrical properties of the different BTO layers and the same dielectric constant and polarization values were obtained whatever the substrate.

Resume : Multilayer ceramic capacitors (MLCC) are one of the dominant passive components in electronic devices. Historically, MLCCs were fabricated using precious metal electrodes; however, to reduce costs cheaper base-metal electrode (BME) devices using Ni and Cu have been developed. BME MLCCs are typically fabricated using a tape casting process, building up multilayers of dielectric interspaced with screen printed Ni electrodes. The devices are subjected to a burnout and sintering process in a controlled reducing environment. In the next step, the devices were oxidised in a partially oxidising atmosphere to reduce the concentration of oxygen vacancies. The nature of the interface between the metal electrode and the dielect¬ric is of paramount importance for the device performance and reliability. Ni oxidation has been investigated in past using several methods including the measurement of oxygen partial pressure, O18 isotope investigation, scanning electron microscopy (SEM), transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDX), electron diffraction and secondary ion mass spectrometry (SIMS). It has been reported that oxygen diffuses much faster in the dielectric than the metal electrode and hence, the metal oxidation takes place at the metal-ceramic interfaces. In this investigation, Ni oxidation in BME MLCCs is being examined using different analytical techniques including X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, SEM, TEM, EDX, and TOF-SIMS.

Resume : Functional oxides are attractive for next generation electronic materials due to their versatile properties. Nanocomposite oxides with heterogeneous structures can allow combinations of useful properties in one film. A notable example is nanocomposites formed from spinel and perovskite which show both magnetism and ferroelectricity but it is possible to take advantage of more versatile functionalities if other functional elements can be contained in nanocomposites. In this work we show the formation of three components nanocomposite thin films formed by the deposition of films from a composite target by sputtering on (001) oriented SrTiO3, silicon substrate. Three component nanocomposites consisted of perovskite, spinel, and garnet phases, for example ferroelectric BiFeO3 (BFO)-ferrimagnetic CoFe2O4 (CFO)-ferrimagnetic Y3Fe5O12 (YIG) or BaTiO3 (BTO)-CFO-YIG. The microstructures and strain states of nanocomposites were characterized by high resolution X-ray diffraction (HRXRD) and transmittance electron microscopy (TEM). The ferroelectricity and ferromagnetism were measured by piezoresponse force microscopy (PFM) and vibrating sample magnetometer (VSM). The resulting three component films exhibited vertically aligned nanostructure consisted of a perovskite matrix containing vertical nanorods of CFO and nanoparticles of YIG. The magnetic behavior changed significantly compared to two component BFO-CFO or BTO-CFO nanocomposites. Magnetic hysteresis loops showed reversal of a soft and a hard magnetic component origiated from CFO and YIG phases.

Resume : Self-assembled nanocomposite thin films which ferromagnetic CoFe2O4 (CFO) nanopillars grow in a ferroelectric BiFeO3 (BFO) matrix have been tremendously attracted for next generation multiple state memory devices. When a ferroelectric BFO and a ferrimagnetic CFO are deposited at the same time using pulsed laser deposition and sputtering, self-assembled epitaxial nanocomposites were grown in which CFO pillars grew in BFO matrix along the same crystallographic direction. Both phases are in good lattice mismatch leading to an epitaxial growth along the vertical direction. The vertical strain at the interface plays an important role in manipulating the magnetic and ferroelectric properties because CFO is a magnetostrictive and BFO is a piezoelectric material. It has been reported that coercive field and magnetic anisotropy of the nanocomposite thin films are critically affected by strain states and aspect ratio of CFO pillars within a BFO matrix. Therefore, controlling the magnetic hysteresis of the nanocomposite thin films by adjusting the composition or geometry of the pillars is necessary to optimize its performance. Herein we showed the preparation of ceramic composite targets and fabrication of the self-assembled nanocomposites using radio frequency (RF) magnetron sputtering. Then we investigated a relation between the strain states and magnetic anisotropy at nanocomposites with variety of BFO:CFO ratios. Finally, we described the effects of pillar length modulation on the strain state and magnetic properties of BFO-CFO nanocomposites. Some samples were selectively etched to remove BFO phase which constrains strain of CFO pillars to confirm the strain effect on magnetic anisotropy.

Resume : Cobalt-based perovskites attract much attention by their unusual electronic, transport, and magnetic properties. The various spin states of cobalt ions responsible for these properties are determined by the competition between the vibrational energy of the lattice and the Hund exchange energy. Among all cobaltites, LaCoO3 (LCO) is an interesting system for studying the transition of the spin state and related phenomena. At the moment, many properties have been studied regarding thick (> 20 nm) LCO films, as well as the presence of stable ferromagnetic ordering at temperatures of ~ 80K [1], which makes it very actual to study the specific dependence of functional properties on the film thickness in range of 5-10MLs. LCO films has been grown using the method of pulsed laser deposition, which provides the possibility of producing ultrathin epitaxial films with a thickness of about 5-10 monolayers. In order to analyze the effect film stress upon growth, different types of substrates and sublayers (LaAlO3, DyScO3, Ir, SrTiO3, LSAT) were used. Further studies were focused as well on the analyzing the composition of the film, its thickness and degree of crystallinity, by means of EDS, XRR, XRD and LEED complimentary techniques. In addition to studies concerning the evaluation of film quality, studies of the magnetostructural properties have been carried out.

Resume : Silicon oxynitrides have been used as the dielectric layer in metal-insulator-metal (MIM) capacitor for many semiconductor devices. Typically, the silicon oxynitride thin films are deposited by PECVD. Dielectric constant of PECVD silicon oxynitride thin films ranges from 3 to 7.5, which is between the dielectric constant of silicon nitride and silicon oxide. However, people note that there are some residual impurities, such as, hydrogen, will bond with silicon (or nitrogen) atoms in PECVD silicon oxynitride thin films and those residual impurities would influence the capacitance. In this work, we deposited silicon oxynitride thin films by sputtering, which can avoid the residual impurities and improve the film quality. Metal-insulator-metal (MIM) capacitor structure was fabricated on glass substrate by magnetron sputtering. The sputtered silicon oxynitride thin films are sandwiched between two copper electrodes as the dielectric layer. Using this MIM structure, the dielectric constant of the sputtered silicon oxynitride thin film is measured to be around 30 at 1 kHz frequency. It is much higher than the reported dielectric constant of PECVD silicon oxynitride thin films. Varying the nitrogen gas flux during sputtering process, the ratio among O-Si-N, Si-O, and Si-N bonds can be manipulated in the sputtered silicon oxynitride thin films, which can be evaluated by XPS analyze. Then, we can observe the relation between the bond structure and the dielectric constant of the sputtered silicon oxynitride thin films. The preliminary results show that the percentage of the Si-N bonds is relatively high in the sputtered silicon oxynitride thin film, compared to other bonds, such as, Si-O, O-Si-N. The rich Si-N bonds in the sputtered silicon oxynitride thin films could be the main reason for the higher dielectric constant of the sputtered silicon oxynitride thin films. PL analysis is also used to clarify the structure effect on the dielectric constant of the sputtered silicon oxynitride thin films. Furthermore, the edge effect would be discussed in this talk, as the size of the top and bottom electrode is not the same.

Resume : Oxides with the general formula ABO3 present a large variety of structural and physical properties. When A cation is small (Goldschmidt tolerance factor t <0.75), the Ilmenite (IL) structure, with A and B in six fold coordination, can be favored instead of the usually observed perovskite structure. Compounds adopting the IL structure display various functional properties, such as weak ferromagnetism, high static dielectric permittivity or semiconducting behavior, finding applications in various fields including photo-catalysis and gas sensing. This work focuses on the preparation of NiTiO3-IL thin films by RF magnetron co-sputtering starting from metallic Ni and Ti targets followed by post-annealing. The aim of this study is to tune the morphological and structural features of the films by changing: 1) the substrate (silicon, Al2O3), 2) the sputtering parameters, and 3) the annealing conditions in air with temperatures ranging from 600 to 900°C. This versatile process allows to adjust the stoichiometry of the films by controlling for every deposition conditions the power ratio of sputtering targets. Chemical composition, morphological and optical properties are investigated by Energy Dispersive X-ray spectroscopy, Scanning Electron Microscopy and optical spectroscopy respectively. The structure is examined by X-Ray Diffraction and Raman spectroscopy. This work links together the processing conditions of NiTiO3-IL films and their structural, morphological and optical features.

Resume : The effects of annealing temperature and film thickness on the crystal structure and ferroelectric properties of Al:HfO2 films were investigated. Ferroelectric MIM capacitors based on aluminium (Al) doped hafnium oxide (HfO2) thin films grown on titanium nitride (TiN)/silicon substrates and Cr/Au top electrodes were fabricated. The structural properties of ferroelectric layers were determined by grazing incidence X-ray diffraction (GIXRD) that showed formation of the orthorhombic phase in Al:HfO2 thin films. Recording and investigating ferroelectric domains in Al:HfO2 thin films was done with Piezoresponse force microscopy (PFM) technique. The atomic force microscopy (AFM) analyses indicate a very low value of roughness average, for all grown thin films, less than 0,25 nm. Electrical characterization were assessed by polarization-voltage (P-V), capacitance-voltage (C-V), and current-voltage (I-V) measurments at room temperature. Relevant changes depending on the thickness and annealing temperature were observed. The post-deposition annealing can influence the film structure by densification and increasing the degree of crystallization.

Resume : In this study we investigate the obtaining of dopant-free hafnium oxide, with ferroelectric properties. Due to the polycrystalline nature of HfO2 films grown by ALD, very small thicknesses of up to ~ 10 nm, as well as mixed orientation and phase composition, by controlling the oxidant dose during the ALD process, it is possible to obtain the monoclinic phase suppression in the hafnium oxide thin films. This suppression of the monoclinic phase involves the development of the polar orthorhombic Pbc21 phase, and implicitly the occurrence of the ferroelectric properties in dopant-free hafnium oxide thin films. Atomic layer deposition method was employed to growth the hafnium oxide thin films with thicknesses below 10 nm. Grazing incidence X-ray diffraction (GIXRD) results showed formation of the orthorhombic phase in dopant-free hafnium oxide thin films, with Pbc21 symmetry. Ferroelectric and electrical properties of the hafnium oxide thin films were assessed by piezoresponse force microscopy (PFM) and I-V and C-V measurements. In conclusion, suppression of the monoclinic phase with the rearranging oxygen vacancies and thickness scaling, is favorable to boost orthorhombic phase and implicitly the ferroelectricity phenomenon in dopant-free hafnium oxide thin films.

Resume : Although ZnO thin films exhibited good resistance-change nonvolatile memory characteristics in terms of switching speed, on-off resistance ratio, and data retention, it is unlikely for the memory device to exhibit stable resistive-switching due to the electrical resistive-switching stresses. In order to improve the resistive-switching properties of ZnO-based ReRAM, a ZnO/SiOx multilayer structure has been proposed; the thickness of SiOx layer should be 1~2 nm. In this experiment, thermal annealing effect on the nonvolatile memory characteristics of the ZnO/SiOx multilayers was investigated. Both ZnO and SiOx thin films were deposited using RF magnetron sputtering technique at room temperature. The ZnO/SiOx multilayers were then annealed with various temperature and time conditions under N₂ gas atmosphere. The nonvolatile memory parameters were measured along the thermal annealing conditions. Reproducible resistive-switching operations with the on-off resistance ratio of >10² were obtained during ~200 cycles. In the presentation, the effect of thermal treatment on the nonvolatile memory characteristics will be discussed with the experimental results.

Resume : Thin films of lead-free 0.5(Ba0.7Ca0.3TiO3) – 0.5[Ba(Zr0.2Ti0.8)O3] (BCZT) were grown by Pulsed Laser Deposition (PLD) on (001)-oriented niobium doped strontium titanate (Nb:STO) single crystals and on platinized silicon substrates. X-Ray Diffraction (XRD) showed highly oriented epitaxial growth (FWHM: 0.08°) of the films on Nb:STO, whereas the films on platinized silicon are polycrystalline with no preferred orientation. However, the use of a 10 nm Nb:STO Seed-Layer on top of the platinum metallization enabled the growth of (111)-textured BCZT thin films (FWHM: 4.2°). The microstructure of the epitaxial films was further investigated by Scanning Transmission Electron Microscopy (STEM) and the occurrence of Edge-type misfit-dislocations at the film-substrate interface was found. Impedance spectroscopy revealed a dielectric relaxation process in the epitaxial films, whereas no relaxation was observed in the polycrystalline films. This may be attributed to different domain wall motion in the films.

Resume : HfO2 is an important material for microelectronic and optical coating applications due to its excellent dielectric properties. When doped, it could be used as a ferroelectric, in memristors or sensors devices. It is well known that HfO2 properties depend on its oxygen content. To optimize its properties one usually optimizes the oxygen pressure during synthesis. We deposited thin HfO2 films with a PLD installation that uses an ArF excimer laser on Si and quartz substrates under various oxygen pressures to optimize their electrical and optical properties. After deposition, the mass density, surface roughness, structure, optical and dielectric properties were investigated using X-ray reflectivity, grazing incidence X-ray diffraction, optical transmittance, spectroscopic ellipsometry, X-ray photoelectron spectroscopy and scanning electron microscopy. However, the electron paramagnetic resonance (EPR) investigations of HfO2 films turned to be the most sensitive technique to oxygen deposition conditions and hence their oxygen content. The defects created due to the presence of oxygen during deposition of the HfO2 film were characterized using EPR. This made it possible to show the dependency between the concentration of defects and the used oxygen concentration, which was regulated by its pressure, and show an exponential increase of the EPR signal (which is directly proportional to the defects in the thin film). Acknowledgements The work presented was funded by Nucleu –INFLPR program and ELI 17/2017 project.

Resume : Ion irradiation has emerged as a powerful tool for the efficient control of uniaxial lattice expansion to fine tune and modulate the otherwise inaccessible complex correlated phases in oxide thin-films. We report the fine tuning of the magnetic moment, ferromagnetic-paramagnetic and metal-insulator transition temperatures in the NiCo2O4 inverse-spinel oxide by creating oxygen deficiencies, employing high energy He-ion irradiation. Tailoring of oxygen vacancies and consequently a uniaxial lattice expansion in the out-of-plane direction drives the system toward the increase of the magnetic moment by two-times in magnitude. The magnetic moment increases with the He-ion irradiation fluence up to 2.5×10^16/cm^2. Our results are corroborated well by spin-polarized electronic structure calculations with density functional theory and X-ray absorption spectroscopic data, which show peak-height change and energy shift of Co-L2,3 and Ni-L2,3 edges driven by the oxygen vacancies. These results demonstrate a new pathway of tailoring oxygen vacancies via He-ion irradiation, useful for designing new functionalities in other complex oxide thin films.

Resume : The antibiotics have been considered as hazardous chemical substances able to modify the equilibrium of the environment due to their high consumption, resistance to biodegradation process and potential risk for humans. In this work, Ti/TiO2/PbO2 anodes consisting of a PbO2 coating growth on the TiO2 interlayer deposited on titanium substrates were prepared combining different deposition technics: electrochemical method using anodization (Anod), electrodeposition (EL), and sol gel spin coating (SG). Different kinds of anodes have been tested for the removal of ampicillin from water by anodic oxidation. The morphology and the electrocatalytic activity of the anodes were investigated respectively by Scanning electron microscopy and electrochemical impedance spectroscopy. The performance of the electrodes was evaluated through high performance liquid chromatography and chemical oxygen demand measurements. Best results were obtained for the Ti/ TiO2SG/ PbO2EL anode exhibiting 64% of COD removal after 5hours of treatment compared to 54% and 31% for Ti/TiO2SG/PbO2SG and Ti/TiO2Anod/PbO2El respectively. HPLC analyses confirm also that faster decrease of ampicillin amount is obtained with Ti/ TiO2SG/ PbO2EL. Thus, the anode prepared by mixing sol gel and electrodeposition is a promising electrode with the best ability for the degradation of ampicillin through anodic oxidation.

Resume : In this study electrical transport in Ti-doped iron oxide films in the temperature range 10 to 473 K was investigated. Iron oxide films were deposited on glass substrates using spray pyrolysis method at a temperature of 450 °C. Here, Iron (III) acetyleacetonate and Titanium diisopropoxide bis (acetylacetonate) were used as the Fe and Ti precursor, respectively, whereas methanol was used as the solvent. The undoped sample were observed to be very resistive in nature, whereas the doped ones were found to be conductive linearly with doping percentage. The UV-Vis transmission spectra showed a transition around 560 nm corresponding to 2.2 eV optical bandgap. The film with 20 % Ti showed a resistance of around 15 kΩ at room temperature. Seebeck coefficient measurement revealed n-type conductivity of the films. Low temperature Hall measurements were carried out using 4-point probe van der Pauw method. The carrier concentration, Hall mobility, and the resistivity of the films were measured to be 3.97 × 1018 cm-3, 1.07 cm2/V•s, and 1.47 Ω-cm, respectively at room temperature. In order to investigate temperature dependent electrical transport, resistivity of the films were measured as a function of temperature separately from 300 to 473 K (above room temperature) and 20 to 300 K (below room temperature). The films showed a normal semiconductor-like inversely-proportional behaviour of the resistivity with increasing temperature.

Resume : Inkjet printing constitutes a cost-effective and energy-efficient deposition method for automated and accurate thin film fabrication and surface patterning, thus making it an advance technology that can be easily integrated into industrial production lines. In this current study the use of inkjet printing for the fabrication of the electrode films of a novel solid oxide fuel cell device, is presented. More specifically, results on the development and optimisation of oxide nanoparticle suspensions/inks and their performance on the fabrication of oxide electrode films by inkjet printing, are discussed, as well as results on the characterisation of the printed oxide electrode films. Study of the agglomeration of particles in the oxides suspension, as well as storage tests were conducted by dynamic light scattering. The thermal degradation and evaporation rate were measured by differential scanning calorimetry and thermogravimetric analysis. Rheological characteristics over temperature were studied by viscometry measurements, while the ink to substrate interactions were tested by contact angle measurements via the sessile drop method. Homogeneity, porosity and morphology of the printed oxide films were observed by optical microscopy and scanning electron microscopy. Printed film thickness was measured by profilometry. The structural and chemical composition of the printed oxides inks through various fabrication steps were confirmed by x-ray diffraction and infrared spectroscopy.

Resume : In this work, the self-organized mixed-oxide nanotubes (NTs) has been fabricated on commercially pure α-phase titanium, single β-phase Ti-24Nb-4Zr-8Sn (Ti2448) alloy and α+β-phase Ti-13Zr-13Nb (Ti1313) alloy. The nanotubular oxide layers were manufactured by means of the electrochemical anodization process which was performed in ethylene glycol-based electrolyte with fluoride ions at constant voltage of 20 V for 2 h. Morphology of the fabricated NTs was characterized by SEM/STEM. Characteristic dimensions describing NTs, such as diameter, wall thickness and height, were determined based on the obtained microscopic images. The chemical analysis was performed by EDS and XPS methods. Despite of applying the same process parameters in all cases, NTs obtained on three different substrates showed a different morphology (e.g. smooth or ribbed walls). The values of diameters and heights of the NTs were different as well. The results of the chemical analysis allowed to determine the stoichiometry of the obtained oxides, their percentage content and distribution in the layer, and to explain the effect of the chemical composition of the substrate on the formation process of nanotubular layers.

Resume : Recent flash memory devices continue to be demanded to be smaller in size and exhibit faster operating speeds and high data storage stability of more than 10 years. In general, these properties strongly depend on the thickness of the tunneling oxide layer of transistors. For the devices of small size with a fast operation speed, it is necessary to reduce the thickness of the tunneling layer, but the tunnel oxide layer thickness in memory devices can hardly be scaled below 8 nm because of the charge loss through the thin tunneling layer. One approach to realize devices with high data storage stability that operate at high speed is to replace the single SiO2 tunnel oxide layer by a low-k/high-k tunnel dielectric stacked layer. Here, we report a simple method for fabricating Sn@Al2O3 core-shell nanoparticle (NP) layer embedded in SiO2, which has the effect of a metallic NP floating gate with a low-k (SiO2)/high-k (Al2O3) dielectric stacked tunneling layer. The core-shell NPs were simply formed by thermally annealing a layered structure consisting of an ultrathin Sn layer between two thin Al layers, where the layered structure of Al/Sn/Al was sandwiched between two thin silicon-rich oxide layers within SiO2. The floating gate with Sn@Al2O3 core-shell NPs was found to have much highly stable charge retention.

Resume : Low resistance large area two dimensional molybdenum dioxide (MoO2) thin crystals were grown on SiO2/Si substrates by chemical vapour deposition (CVD) method. The MoO2 crystals were synthesized by direct evaporation of MoO3 and also sublimation of MoO3 in presence of sulfur precursor inside CVD reactor at a higher temperature in presence of an Ar atmosphere, respectively. The grown crystals were large in size (up to 20µm in length) with a rhomboidal shape and also highly crystalline in nature with a height of few nanometers. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and atomic force microscopy were used to study the as grown MoO2 crystals. The electronic properties of MoO2 crystals were studied by fabricating devices using an individual crystal, with Pt serving as contacts from the two opposite sides of the MoO2 crystal. The thin crystals exhibited a comparatively high electrical conductivity. Keywords: Molybdenum dioxide (MoO2), Chemical vapour deposition (CVD), Electrical conductivity

Resume : In the last years, the global warming represents one of the biggest problem for our environment and it needs to be urgently solved. Photocatalysis using perovskite materials is considered to be the key of solving energy problemes, because this reaction type can use sunlight that is a clean and renewable energy source. Lanthanum ferrite (LaFeO3-LFO) and bismuth ferrite (BiFeO3-BFO) are possible candidates as photocatalysts due to high light absorption properties. In this work, we report the functional photoelectrochemical properties of different heterostructures BFO/LFO and LFO/BFO thin films obtained by pulsed laser deposition (PLD). The purpose of this survey was to combine the strong ferroelectricity and high chemical stability of BFO with the great absorption properties of LFO, generating in this way new photocatalysts with enhanced activities in photocatalytic reactions. Moreover, the influence on the water splitting reaction of the oxygen content and the induced strain defects in the perovskite structure was studied. X-Ray diffraction and high resolution electron microscopy (HR-TEM) techniques were used to study the structural properties of the obtained thin films, while the topography was analysed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The absorption properties were obtained by spectroscopic ellipsometry (SE), the band gap value being calculated using Tauc plots.

Resume : Smart nano-multifunctional complex oxide heterostructures such as metal insulating transition (MIT) thin films grown on different substrates and free-standing nanowires have recently received a renewed attention due to their promising novel nanotechnological applications and breakthrough in switching, sensing, energy-efficient smart windows and nonvolatile read access memories. There are several factors, which make this review particularly timely and important. Firstly, there is a market pressure, primarily from the nanoelectronic industry and energy sectors to develop highly efficient novel multifunctional optoelectronic nano-devices at low cost through process optimisation and band gap engineering. Secondly, there is an opportunity for novel exploration, new functionality and breakthrough at interfaces of these thermoelectric materials due to the recent developments in thin film growth and nanofabrication technology. Thirdly, there is a need to fully understand the intrinsic size effects on MIT performance at nanoscale in the absence of extrinsic factors. This feature review attempts to discuss thin film deposition and nanofabrication technological techniques of multifunctional complex oxide nanostructures including vanadium dioxide (VO2) MIT thin films on different substrates and free-standing nanowires. In particular, the evolution of thin film deposition and free-standing nanowires fabrication techniques using pulsed laser deposition (PLD), chemical vapour deposition (CVD), plasma enhanced chemical vapour deposition (PECVD), focused ion beam (FIB), thermal evaporation and sputtering systems are technically and critically reviewed.

Resume : Strain gauges are electromechanical sensors that measure the mechanical distortion of any objects. Recently, different types of strain gauges have been applied to a variety of devices such as wearable electronics, electronics skin, health care system, etc. Among different strain sensors, the resistive type strain sensor is the simplest form and has attracted huge attention due to low cost and high performance. Resistive type strain sensors function by reading the resistance change upon an application of external strain to objects. Recently colloidal nanocrystals (NCs) have been considered as new promising materials for strain sensor owing to their unique properties. In this study, we introduce a strategy to introduce solution-processed interfacial layers in nanocrystal (NC) thin films to fabricate high-performance strain sensors. SiO2 interfacial layers are chemically introduced in ligand-exchanged Ag NC thin films to increase the tunneling gap or inter-particle distance between each Ag NC. In this way, the charge-transport mechanism is manipulated, leading to unique electromechanical properties with a high gauge factor. All solution-processed strain gauge sensors with high stability, durability, and sensitivity are fabricated. The sensor successfully measured delicate movements such as finger motions, demonstrating its possible application in electronic skin.

Resume : Integration of high quality complex oxides thin films, such as the multiferroic BiFeO3 (BFO) material, is required for the oxide electronics development. However, due to properties related to the crystalline orientation, optimal performances are mainly obtained on expensive single crystalline substrates. A lower cost alternative route would be the use of oxide nanosheet seed layers being able to be deposited on all types of substrates, in particular silicon (Si), which would allow to obtain complex oxides with desired crystallographic orientation and their integration in CMOS technology. In this work, BFO films were deposited by Chemical Solution Deposition (CSD) based on polymeric precursor method. First, the optimization of synthesis parameters were performed on amorphous silica and transposed on (100) Si substrates. The structural and microstructural characterizations have revealed a polycrystalline growth on both substrates and the strong influence of the synthesis temperature, in particular to obtain the pure perovskite phase. The influence of a two-dimensional nanosheet seed layer (2D-NS) was then investigated. From exfoliation of the lamellar niobate KCa2Nb3O10 prepared by solid state reaction, Ca2Nb3O10- nanosheets layer was deposited directly on Si substrates by Langmuir Blodgett process, followed by the subsequent deposition of BFO by CSD. X-ray diffraction measurements have evidenced (100) oriented BFO thin films confirming the great interest of 2D-NS seed layers.

Resume : ZnO thin films have been widely investigated for ReRAM(Resistive Random Access Memory) applications, and the nonvolatile memory properties, such as fast switching speed, large on/off-resistance ratio, moderate endurance, and long retention, were revealed. Here, we consider using Zinc Silicate (ZnSiO₃ or Zn₂SiO₄) as a new material for ReRAM application in order to improve various nonvolatile memory characteristics. Zinc Silicate thin films were deposited on a highly doped Si substrate by RF-magnetron sputtering method. We observed that the new Zinc Silicate thin films occasionally exhibited bipolar or unipolar resistive switching properties. In the bipolar operation, the set- and reset- voltages were around 3.5 V and -2.8 V, respectively. Current ratio of Low Resistance State (LRS)/High Resistance State (HRS) was 10². In the case of unipolar operation, the set- and reset- voltages were around 3.8 V and 1.2 V, and current ratio of LRS/HRS was ~10⁴. It should be noted that the unipolar operation showed not only larger resistance on/off ratio and lower reset voltage but also better endurance behavior than those of bipolar operation. However, the HRS of unipolar operation was unstable in endurance measurements. We speculated that the large current-fluctuations in HRS of the unipolar operation could be attributed to non-repeatable formation of the nonstoichiometric phase of Zinc Silicate. These results point to the possibility of using a Zinc Silicate thin film for ReRAM devices. Further experiments are necessary to understand its resistive switching mechanism and improve the nonvolatile memory properties.

Resume : β-Ga2O3 is a transparent semiconductor material that has attracted a lot of interest in recent years due in part to its large band gap (~4.7 eV at room temperature) giving rise to its good transparency and high breakdown field (8 MVcm-1). These properties make β-Ga2O3 attractive for a whole host of applications, such as high power electronics, solar-blind UV detectors, and gas sensors. Whilst β-Ga2O3 is a very promising material, many of its fundamental properties have yet to be fully explored. One question relates to the surface electronic properties of this material. A few recent reports claim that β-Ga2O3 displays electron depletion at the surface, but with insufficient evidence and incorrect data analysis this question still remains. Here we use a combination of x-ray photoemission spectroscopy with high-quality single crystalline (2 ̅01) β-Ga2O3 and state-of-the-art density functional theory in order to determine the surface electronic properties of β-Ga2O3. Contrary to previous reports, we observe downward band bending (electron accumulation) at β-Ga2O3 surfaces when atmospheric contaminants are present, a phenomenon never before investigated for this material. In-situ cleaning shows a transition to upward band-bending. Finally, we investigate the effect of hydrogen at the surface and in the bulk of β-Ga2O3, showing its responsibility for the band bending transition observed.

Resume : The materials that perform upconversion are often used in optoelectronic devices, solar cells, safety inks, three-dimensional imaging devices, biological and medical applications due to energy conversion. 2D oxide nanosheets, a member of the 2D family of materials, are obtained by a chemical exfoliation of layered oxide bulk materials. The thickness of the 2D oxide nanosheets varies from one nm to several nanometers depending on the chemical composition of the host part of the layered material. In this study, the Ruddlesden-Popper type K2Ln2Ti3O10 (Ln: lanthanide) layered perovskite doped with Yb3 /Er3 , Yb3 /Tm3 , and Tm3 /Er3 ions were exfoliated to produce single Ln2Ti3O10 nanosheets. These nanosheets that have upconversion properties were used to fabricate nanofilms by the layer-by-layer method. The nanofilms having ~50 nm thickness assembled by joining a combination of these nanosheets have exhibited emission in different parts of the visible region by upconversion depending on the amount of doping with lanthanides, the annealing temperature of the layered materials, the order of the nanosheets during the nanofilm fabrication and thickness of the nanofilms. The characterization of the nanosheets and nanofilms were performed using Atomic Force Microscopy, X-ray Diffraction Spectroscopy, Scanning Electron Microscopy-EDX, Inductively Coupled Plasma and UV/VIS/NIR Spectroscopy techniques.

Resume : Manganese based perovskites (“maganites”) of the composition A1-xBxMnO3 appear in various electronic and magnetic phases, with features like colossal magnetoresistance. Those phases are composition and temperature dependent as shown in complex phase diagrams. The complexity of this system originates from competition between order mechanisms, magnetic interactions and structural aspects. The macroscopic phase diagram is believed to be an overlap of small phases where the disorder that is induced by the distribution of A3+ and B2+ and the ratio of Mn3+/Mn4+ results in local variation of the mechanisms mentioned earlier. During this project, we want to cross magnetic phase boundaries reversibly by chemical doping and monitor the process in-situ. To achieve this, we want to use electrochemical lithium intercalation and de-intercalation. The material of choice is La1-xSrxMnO3 (LSMO) where lithium would replace part of lanthanum or strontium. At a composition of 50% strontium and at room temperature LSMO shows a phase transition between ferro- and paramagnetism. It is believed that one could switch between those magnetic states by lithium inter- and de-intercalation. Furthermore, the in-situ measurements are carried out using polarized neutron reflectometry (PNR) and the Van der Pauw method. With PNR, we investigate the distribution of the Lithium and the magnetic induction profile. With Van der Pauw we measure the change of conductivity and li-ion transport. Another goal is to relate these phenomena to the Mn3+/Mn4+ ratio. Because the process should be reversible we want to investigate the same sample in various states along the phase transition border using various methods and connect the different appearing phenomena as mentioned above to each other.

Resume : Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) are electrochemical energy converters using renewable fuel such as hydrogen. Their performances are strongly related to the catalytic/conductive properties of cathode materials, which are temperature dependent. For practical application, the optimal operating conditions imply a tradeoff between high efficiency at high temperatures and improved lifetime at intermediate temperatures (below 1000°C). Among the candidates, Pr2NiO4 has good functional properties but is susceptible to decompose to Pr4Ni3O10 under IT-SOFC conditions. In this contribution, the Pr4Ni3O10 phase has been directly targeted as a potential alternative to Pr2NiO4. Pr4Ni3O10 thin films have been deposited on Y-stabilized Zirconia substrates through a twostep process: i) room temperature co-sputtering of metallic Ni and Pr targets, ii) ex-situ annealing under oxygen flux. The composition of thin films were adjusted by changing the power applied to each targets and controlled by Energy Dispersive Spectroscopy. The optimal annealing conditions were identified by X-Ray Diffraction analyses as a function of temperature up to 1200°C. These analyses revealed that the system showed the evolution from single metal oxides to Pr4Ni3O10 phase above 1000°C, which finally transformed to Pr2NiO4 above 1050°C. Finally, the impact of deposition conditions on the structural and morphological features of the Pr4Ni3O10 films were studied by electron microscopy techniques.

Resume : Multilayer ceramic capacitors (MLCC) are electronic components used for charge storage and switching applications in a wide range of products such as automotive components, smart phones, computers digital cameras, etc. To improve performances, such as volumetric capacitance, MLCC are miniaturised, with thinner dielectric layers, made of smaller individual barium titanite (BT) crystal grains and this is a challenge as smaller grains have reduced permittivity. The other issue is to improve the reliability of these devices as MLCC are processed within a unique manufacturing process which result in oxygen vacancies within the BT layer. After prolonged or repeated usage, the evolution of these defects can result in a drop in the internal resistance and device failure [1] In this study, we investigate this issue on cross-sectioned and polished MLCC devices in pristine and aged conditions; the ageing being carried out using highly accelerated life testing (HALT) [2]. FE-SEM and AFM microscopy show no significant changes in Ni electrode morphology, topography and continuity. Nanoindentation showed that the aged BT was harder that the as received one. Finally, scanning Kelvin probe microscopy (SKPM) show an asymmetry between anode and cathode voltage and field concentration near interfaces. Hence, these techniques have the ability to show changes within the dielectric layer but also at the Ni/BT interfaces, which can contribute to our understanding of ageing mechanisms and help optimise device reliability. 1. T Tsurumi, M Shono, H Kakemoto, S Wada, K Saito , H Chazono Mechanism of capacitance aging under DC-bias field in X7R-MLCCs, J Electroceram (2008) 21:17–21 2. AM Hernández-López, JA Aguilar-Garib, S Guillemet-Fritsch, R Nava-Quintero, Pl Dufor, C Tenailleau, B Durand, Z Valdez-Nava, Reliability of X7R Multilayer Ceramic Capacitors During High Accelerated Life Testing (HALT) Materials 2018, 11, 1900

Resume : Lead-based ferroelectric materials, such as: PbTiO3, PbZrxTi1-xO3 (PZT), La-doped and Nd-doped Pb(ZrxTi1-x)O3 (PLZT), and (PNZT) are widely used in micro- and nanoelectronics. During practical use lead zirconate titanate have problems with to high coercive field and leakage current, short retention, tendency to imprint, and fatigue with usual platinum electrode. These properties of PZT thin films depend on substrate materials, deposition method using measurement frequencies, at al. The deposition conditions, such as: deposition rate, composition and substrate temperature are very important factors in the growing process for PZT film formation. Thin film growth by reactive magnetron layer-by-layer deposition method in vacuum is one of the most promising methods for perovskite phase PZT thin films formation without post annealing. Lead zirconate titanate thin films were grown on a platinum covered silicon substrate using layer-by-layer reactive DC magnetron deposition method. Deposition was done in a 1 Pa oxygen environment on heated substrates (400-600oC). Atomic composition of surface of as-deposited thin films was studied using X-ray photoelectron spectroscopy (XPS). Layer surface was inspected using optical, scanning electron, and atomic force microscope. The crystallographic structure of thin films was investigated with X-ray diffraction (XRD). Polarization dependency on the electric field strength was measured. The frequency was changed from 20Hz to 1MHz. Dielectric properties of lead zirconate titanate (PZT) thin films were measured from 20 Hz up to 100 kHz during cooling cycle at 1K/min cooling rate using Hewlett Packard 4284A precision LCR meter. Dielectric hysteresis was obtained using aixACCT TFAnalyzer 2000 E system. It was obtained that the Pb(Zr0.58Ti0.42)O3 composition film with the dense and uniform morphology was formed at 550°C substrate temperature. It was shown that the microstructure of the deposited films strongly depend on the substrate temperature. The films exhibit columnar growth at all investigated deposition temperatures. P–E hysteresis loops of PZT thin film deposited at 550oC, exhibiting the highest remnant polarization (25µC/cm2) and coercive field (280kV/cm). The sample has relatively low dielectric permittivity, which is around 150.

Resume : The understanding of low-temperature oxygen interaction and diffusion in ultrathin oxide films is a significant challenge. In this work, we analyze the oxygen-oxide interaction through isotope exchange depth profiling (IEDP) with low energy ion scattering (LEIS). The high sensitivity of LEIS enables the correlation of isotope exchange kinetics at surfaces and in-depth penetration with high accuracy. This method was applied to films of zirconium oxide (ZrO2) and molybdenum oxide (MoO3) of 2 to 10 nm, reactively deposited via DC magnetron sputtering. After deposition, the samples were transferred in vacuum and analyzed prior and after exposure to atomic O-16 and O-18 generated by a plasma gun (10^15 atoms.cm^-2.s^-1) at room temperature. With the diffusion profiles obtained, diffusion modes and parameters were determined based on models stated in the literature. In both stoichiometrically deposited oxides, the total penetration depth was not influenced by the layer thickness. However, isotope diffusion was shown to be strongly influenced by the presence of metallic and sub-stoichiometric oxide species. In all cases, a higher isotope diffusion constant was observed in the outermost few monolayers at the surface, with no indication of bulk diffusion through the film. These factors indicate that the oxygen penetration is driven by the formation of a space-charge layer in the oxide surface, a consequence of band bending of the oxide induced by adsorbed atomic oxygen species.

Resume : Epitaxial strain engineering in nanostructured materials has attracted great attention to various electrochemical devices such as solid-oxide fuel cells, all solid-state lithium ion batteries, and semiconductor devices. Especially, notable achievement for enhanced ion transport has been reported in ultra-thin epitaxial and multi-layered films. However, the epitaxial strain engineering is mostly limited below a critical thickness, at which strain is relieved by misfit dislocation. As a result, strain in most oxide thin films is fully released above about 20 nanometer thickness, which hinders application of strain effect to electrochemical devices. Above the critical thickness, herein, we investigate strain effect on fast oxygen ion transport in co-doped ceria thin films. To reliably explore the strain effect on ionic transport property, well controlled out-of-plane conductivity measurement was performed for co-doped ceria thin films. In addition, average strain and strain distribution in thin films was analyzed through HR-XRD and strain mapping in TEM. Consequently, we found that co-doped ceria thin film could be strained by growth strain through the Volmer-Weber (island) growth mode, and also by local lattice strain induced by difference of ionic radius between major dopant and minor codopant. From this presentation, you will get a great inspiration to effectively apply the strain effect to improve performance of various electrochemical devices.

Resume : Nickel-Gadolinium Doped Ceria (Ni-CGO) anodic films of 300nm thickness (T1), were deposited on 50~300µm thick (T2) zirconia electrolyte supports, by radio frequency (RF) sputtering. The sputtering was done at 25°C and the RF power (P) was varied between 50~200W. Lanthanum Strontium Manganite (LSM/YSZ) cathodes were screen-printed on the other side of the supports. The solid oxide fuel cells (SOFCs) were tested for maximum power densities under the product fuel of CO2 electro-reduced via industrial waste carbon(IWC)1 at a temperature (C) range of 600°C ~ 800°C by voltage (V)-current (I)-power curves. The resistances of various cell components were measured by nyquist plots. From the results of these electrochemical measurements, a fuzzy model was built with T1, T2, P, C, & V as inputs and I as output. Then, the particle swarm optimization (PSO) algorithm was applied to obtain the optimal parameters of the SOFC, which maximizes its power density. Furthermore, high resolution scanning and transmission electron 2D images were used to build an electrochemical model to simulate the reaction kinetics of these optimized IWC-SOFCs. The results showed that the PVD Ni-CGO based IWC-SOFC’s power density can be increased by 45% when using the PSO algorithm when compared with experimental results. Reference 1. W. H. Tanveer, H. Iwai, W. Yu, A. Pandiyan, S. Ji, Y. H. Lee, Y. Lee, K. Yaqoob, G. Y. Cho and S. W. Cha, Journal of Materials Chemistry A, 2018.

Resume : Two-dimensional metal oxide nanosheets are the oxide equivalents of graphene. They are made by delamination of layered metal oxides in water using a combination of acid-base & ion exchange reactions, or by direct bottom-up growth from chemical solutions. The resulting nanoflakes have thicknesses of 0.5-2.5 nm and lateral sizes between 100 nm and tens of micrometers, depending on composition and synthesis process. A wide range of (doped) oxide compositions and 2D planar structures can realized with these methods. Two applications of oxide nanosheets will be demonstrated in this presentation: (1) Nanosheets are 2D single crystallites with only one type of surface termination. As such, they are versatile seed layers for growth of oriented and epitaxial functional metal oxides. Oriented perovskite-type thin films of SrRuO3, (La,Sr)MnO3, Pb(Zr,Ti)O3 and BiFeO3 have been grown on Ca2Nb3O10 and Ti0.87O2 nanosheets using pulsed laser deposition. Depending on the nature of the seed layer, either [001] or [110] oriented perovskite films are formed, and the ferromagnetic and piezoelectric properties are controlled by the domain size and preferential orientation of the as-grown films. (2) MnO2 nanosheets are suitable as active electrode elements for micro-supercapacitors owing to their composition, conductivity and large specific surface area. The fabrication of nanosheet-based microsupercapacitors by ink-jet printing on flexible plastic substrates is demonstrated. As will be shown, their device characteristics are similar to state of the art supercapacitors.

Resume : La0.67Sr0.33MnO3 (LSMO) thin films have been deposited by pulsed laser deposition onto glass substrates (GS) coated with Ca2Nb3O10- nanosheets (NS). NS have been prepared by exfoliation process of KCa2Nb3O10 powder and deposited onto GS using the Langmuir-Blodgett method with different coating levels (fully, intermediately and non-coated substrates). X-ray diffraction and Electron backscatter diffraction mapping confirm the effect of NS to induce the epitaxial stabilization of LSMO films with a strong out-of-plane (001) texture, whereas the growth of LSMO films on pristine substrates exhibit a non-textured polycrystalline phase. The growth temperature was also investigated and demonstrates that the properties of LSMO film deposited on NS at 550°C are close to those the 650°C one whereas a strong degradation of the LSMO crystalline structure is observed without NS. Transport and magnetism measurements have shown that LSMO films grown on NS coated GS exhibit physical properties close to those of a monocrystalline LSMO film deposited on (001)-oriented SrTiO3 substrate used as reference. In contrast, LSMO polycrystalline films have physical properties close to those of the bulk material. This study demonstrates the opportunity to integrate functional (001)-textured LSMO thin films of high quality on GS using a Ca2Nb3O10- NS layer as growth template. The use of a NS layer offers new perspectives for the integration of functional materials on any substrate at moderate temperature.

Resume : Neuromorphic computing, which resembles synaptic functions of biological neural networks, is emerging as one of the most viable successors of current computing paradigms. The use of established deposition techniques, the safeguarding of Si compatibility, along with the precise control of synthesis, processing and characterization of multifunctional oxide films, is expected to mitigate current CMOS technology bottlenecks, through the production of two-terminal synaptic devices, structured in crossbar arrays. Herein, we present the fabrication of a synaptic device based on the electrochemical delithiation of a highly stoichiometric LiCoO2 (LCO) cathode, and the insertion of the mobile Li ions in a host anode. Deviation from stoichiometry, caused by Li removal, leads LCO to an abrupt resistive switching (RS) with 4 orders of magnitude resistance change, when directly deposited on SiO2(native)/Si substrates. Unlike most filamentary RS devices, a homogenous underlying mechanism is proposed. In order to observe the homogenous RS, a TiO2 anode has been employed, rendering (Au)/LCO/SiO2/TiO2/(SiO2/Si) two terminal devices. Ti is sputtered on Si, and subsequently transformed to TiO2 by in-situ oxidation during the deposition of the LCO overlayer. Highly-stoichiometric, high-temperature (HT) LCO is deposited on top of the Ti layer, via PLD, in an O2 atmosphere at 600 °C, which leads to the in situ oxidation of the Ti into TiO2. Direct deposition of LCO on Ti, however, is conducive to the formation of interfacial parasitic LixTiyO4 phases, reducing the HT-LCO phase, hence limiting the RS effect. It is hereby shown that interposition of a thin sputtered a:SiO2 layer impedes the thermal reaction of Li with Ti, but allows the diffusion of oxygen for the in situ oxidation of TiO2, thus enabling the implementation of synaptic functionalities based on a homogenous RS mechanism.

Resume : Recent developments in thin-film growth showed the enormous potential of epitaxial stress to tune the properties of thin films. In transition-metal oxides (perovskites, spinels, etc) strain accommodation occurs through the modification of bond-distances and angles, which determines the relative orbital occupation. An important question is whether the ccommodation of epitaxial strain can be modified by growing the films under very different conditions, thus allowing the system to explore different relaxation paths. Here we describe a comparative study of perovskite La2/3Sr1/3MmO3 (LSMO) and spinel CoFe2O4 (CFO) thin films grown by pulsed laser deposition (PLD; far from thermodynamic equilibrium), and by a chemical deposition method (polymer assisted deposition, PAD; close to thermodynamic equilibrium). Our results demonstrate that the elastic and magnetic properties of these oxides are largely determined by the proximity to thermodynamic equilibrium during growth. For example, we have found that the pattern of rotation of MnO6 octahedra in LSMO depends very much of the growth conditions. As a result, the relative contributions to the magnetic anisotropy in this oxide can be controlled during deposition.[1] For the case of CFO, we observed that the cationic arrangement among the different voids of the structure also depend on the growth conditions. As a result, a progressive change in the sign of the Poisson ratio can be induced in thin films of CFO in response to epitaxial stress and temperature, defining a smooth crossover from auxetic to non-auxetic behavior depending on the growth conditions.[2] The results presented in this work are of general applicability for understanding the stress-relaxation mechanism in complex crystalline structures. [1] J.M. Vila-Fungueiriño et al. J. Phys. D: Appl. Phys. 49, 315001 (2016). [2] E. Ferreiro-Vila et al. submitted.

Resume : The Fermi energy in semiconductors can often be freely controlled across the whole energy gap by doping. This is not the case in oxides, where different mechanisms exist, which can limit the range of the Fermi energy. These limits can be caused by i) dopants having deep rather than shallow charge transition levels, ii) self-com-pen¬sation where the Fermi energy dependence of the defect formation energy leads to spontaneous formation of compensating defects, iii) the change of the oxidation state of either the cations or the oxygen. The latter is particularly relevant for compounds with transition metal or rare earth cations and has been recently demonstrated to explain the low water splitting efficiency of hematite. It will be demonstrated how the limits of the Fermi energy can be assessed using X-ray photoelectron spectroscopy (XPS). The variation of the Fermi energy can thereby be achieved either by deposition of thin films on different substrates, by deposition of differently doped films, by different surface treatments including oxygen and vacuum annealing, oxygen plasma treatments and water adsorption, or by formation of interfaces with low and high work function metal oxides. Extensive data sets for various oxides, including dielectric, semiconducting and ionically conducting materials are available. The effects will be illustrated using selected materials and the alignment of the Fermi energy limits will be discussed.

Resume : Spinel ferrite thin films have numerous technological applications in areas such as telecommunications (microwave and millimeter wave devices), magneto-electric coupling devices and are also promising candidates for future spintronic devices. Unlike perovskites, the investigation of high quality spinel ferrite films is quite limited, in part because of the complex crystal structure with a large unit cell consisting of many interstitial sites and that the transition metal cations can adopt various oxidation states. Usually films of spinel ferrite such as NiFe2O4 (NFO), grown both by both physical and chemical deposition techniques, suffer from a number of structural and magnetic drawbacks, e.g. formation of antiphase boundaries and high magnetic saturation fields. We show that by using substrates having similar crystal structure and low lattice mismatch, one can avoid formation of antiphase boundaries and thereby obtain magnetic properties comparable to bulk single crystal. We used spinel MgGa2O4, CoGa2O4 and ZnGa2O4 substrates, which have 0.6%, 0.1% and 0.05% lattice mismatch, respectively, with NFO to grow epitaxial films that are essentially free of antiphase boundaries and exhibit sharp magnetic hysteresis characteristics. Moreover, ferromagnetic resonance linewidths similar to those in single crystals are obtained. We have compared these results with NFO film grown on another spinel substrate MgAl2O4, which has 3.1% lattice mismatch, that has antiphase boundaries and clearly exhibits degraded properties. We have also investigated spin transport properties of the films grown on the three substrates via the longitudinal spin Seebeck effect (LSSE). An increase in the spin voltage signal with reduction in lattice mismatch is observed, which is in correspondence with similar improvements in structural and magnetic properties. Improvements in the magnetic and spin Seebeck properties are also observed using the lattice-matched substrates for other spinel ferrites, including CoFe2O4 and Fe3O4.

Resume : Bismuth iron garnet (Bi3Fe5O12; BIG) is an insulating ferrimagnet[1]. It possesses functional properties e. g. giant Faraday rotation[2] and magnetoelectric coupling[3]. To further develop its field of potential applications, we aim at enhancing its electrical properties while preserving a robust magnetism. A co-doping strategy is used to synthesize B(CaxY0.5-x)IG thin films. Ca2+ is expected to induce hole carriers while Y3+ is used to control the magneto-optical properties driven by the Bi content. B(Ca0.3Y0.2)IG and B(Ca0.0Y0.5)IG present p- and n-type semiconducting behaviour with resistivity values of 1000 Ω.cm and 10 Ω.cm at 450 K, respectively. A reversible resistive change is unveiled in the n-type B(Ca0.0Y0.5)IG when annealed under neutral/oxidizing atmosphere; the underlying physical mechanisms originating from the oxygen vacancies’ variation[4]. Advanced Scanning Transmission Electron Microscopy coupled with Electron Energy-Loss Spectroscopy (Cs-STEM/EELS) allows us to probe and map locally absorption edges to reveal the atomic and electronic structures. Here, Ca/Y solubility in the BIG lattice was confirmed by STEM/EELS. At higher energy resolution, a clear Fe2+ increase was probed in the B(Ca0.0Y0.5)IG low resistivity state and accounts for the oxygen release. In the p-type B(Ca0.3Y0.2)IG no evidence of Fe4+ could be found indicating a self-compensation with oxygen vacancies. [1] Oikawa JPSJ 74 (2005) [2] Deb JAP 45 (2012) [3] Popova APL 110 (2017) [4] Teurtrie in preparation (2019)

Resume : Atomically sharp heterointerfaces of correlated oxides, given their structural and chemical compatibility, host a rich variety of new electronic and magnetic phases with astonishing properties [1,2]. The emergent phenomenon at the interface is the result of the precise modification of the orbital, electronic, and magnetic structures of the individual constituent layers. The prominent example of such modification at oxide interface physics is high mobility two-dimensional electron gas at the interfaces of two insulators, conducting ferromagnetic layer at an interface of two antiferromagnetic insulators, and orbital reconstruction of electronic systems [1,2]. In particular, heterostructures have served as a sensitive probe by using proximity to an ordered system to bring out latent ordering in an otherwise disordered material. Here, we present a bilayer system composed of SrRuO3, a ferromagnetic metal [3], and CaRuO3, a paramagnetic metal [4]. A detailed experimental study of SrRuO3-CaRuO3 bilayers with various relative widths shows a single magnetic transition temperature which is close to the bulk Tc of SrRuO3, and a net ferromagnetic moment in all samples. At high temperatures, immediately below Tc, the strength of the net moment is directly correlated with CaRuO3 width, while it is inversely correlated at low temperatures. The magnetization results are corroborated well with the transport studies indicating the significance of the conduction electrons in the system. Based on these results, we argue that the CaRuO3 layer develops an oscillating polarization with two contributions: local moments and conduction electrons. The conduction electrons develop Friedel-like oscillations in polarization due to the boundary condition imposed by the ordered SrRuO3 layer. This is inherited by rigid local moments at low temperatures. We also present a simple theoretical model and ab initio simulations to support our picture. 1. H. Y. Hwang et al., Nature Materials 11, 103 (2012). 2. J.H. Ngai et al., Annu. Rev. Mater. Res. 44, 1 (2014). 3. G. Koster et al., Rev. Mod. Phys. 84, 253 (2012). 4. G. Cao et al., Phys. Rev. B 56, 321 (1997).

Resume : Cobalt ferrite, CoFe2O4, (CFO) crystallizes in a spinel structure with the Fd-3m space group. This material has been widely studied for its potential application in electronic devices. The applications require the elaboration of CFO in thin films. While the structure of CFO is very often not cubic any more in these thin films, and while this may have a tremendous impact on their physical properties, there has been until now no determination of the exact structure adopted by CFO in thin films. CFO thin films have been elaborated on MgO (100) at 400°C by pulsed laser deposition with various O2/N2 deposition pressures. Cell parameters and magnetic properties have been investigated as a function of partial pressures. Crystallographic characterizations performed on the samples pointed out a tetragonalisation of the unit cell as a function of the deposition pressure, from c/a > 1 for P < 0.04 mbar to c/a < 1 at high pressure. One of the main consequences of this distortion is the tailoring of the easy direction of magnetization from in-plane at low pressure to out-of-plane at high pressure. This breaking of the original cubic symmetry is therefore the keypoint for the understanding of the physics of these phases and the crystal structure has to be precisely determined. This is a complicated task because of the small amount of matter available in thin films. We were able to complete it via a synchrotron-based resonant X-ray diffraction technique. Diffraction Anomalous Near Edge Structure (DANES) experiments have been recorded at both the cobalt and iron edges using the D2AM experiment set-up of the ESRF BM02 beamline. We then performed a crystallographic Fd3m subgroups analysis and were able to fully determine the crystal structure of the films.

Resume : Antiferromagnetic (AFM) oxide materials in low-dimensional geometries, either in nonmagnetic or magnetic environments, display a rich variety of magnetic behavior. They are very interesting materials to investigate the fundamental physics of finite-size effects in magnetic systems. Despite the limited applications in current technology, AFM oxides are important reference and model systems for studying the interface coupling phenomena that are ultimately exploited in devices such as spin-valves. Furthermore, they are the current focus for next generation of spintronic devices. Here we demonstrate a route for preparing high quality ultrathin ternary transition metal oxide films on a metallic substrate. Nickel oxides with a small content of iron have been grown on Ru(0001) by oxygen-assisted molecular beam epitaxy at elevated temperatures (1150 K). The nucleation and growth is observed in real time by means of Low Energy Electron Microscopy (LEEM. This enables the optimization of the growth parameters. A comprehensive characterization is performed combining LEEM and LEED for structural characterization and PEEM (PhotoEmission Electron Microscopy) with synchrotron radiation for chemical and magnetic analysis via X-ray Absorption Spectroscopy and X-ray Magnetic Linear Dichroism (XAS-PEEM and XMLD-PEEM, respectively). We have been able to obtain high quality 2D islands with atomically flat surfaces and a low density of defects. The high crystalline and morphological quality result in optimized properties with respect to films grown by other methods, such as magnetic domains whose size are larger by several orders of magnitude.

Resume : The focus of research in Spintronics currently aims at reducing the energy cost for magnetic memory bit manipulation, with particularly great implications for the magnetic storage industry. A possible route involves the control of magnetization through spin current based torque such as Spin-Orbit Torque (SOT). SOT can be realized in a bilayer system where one layer is magnetic, and the second layer is a non-magnetic metal with a high spin-orbit coupling (SOC). In the non-magnetic metal, a spin current is generated via the Spin Hall Effect (SHE) and can be injected into the magnetic layer through the interface. A net torque affects the magnetic layer state. We have considered constructing such a device using Ga2-xFexO3 (GFO) as the magnetic layer and platinum as the non-magnetic layer. GFO, apart from being ferrimagnetic at room temperature, also possesses a strong magneto-electric (ME) coupling which makes it possible to have electric field control of magnetization. We will investigate the impact of the ME effect on the SOT in such GFO/PT bilayer. Using a low energy consuming electric field, the magnetization of GFO can be tuned, offering new avenues towards the decrease of the critical current needed to switch magnetization by SOT. In this work, we will demonstrate the optimization of Ga0.6Fe1.4O3 (001) thin film growth by pulsed laser deposition on SrTiO3 (111) substrates in order to achieve atomically flat surface. Interface quality with the top platinum layer is indeed critical for the SOT efficiency. We have observed the influence of the deposition parameters (fluence, repetition rate, deposition atmosphere and substrate temperature) and films thickness on the surface quality and crystallization. We report the crucial parameters required for obtaining atomically smooth growth. The samples characterizations include structural characterization of the deposited material using X-ray diffraction, RHEED, and transmission electron microscopy, as well as topography by atomic force microscopy. The magnetic properties are probed by SQUID magnetometry and the thickness dependence of the GFO magnetic properties will be presented.

Resume : Generation, transportation and detection of spin in a control manner are very important in spintronic devices [1] There are several ways to generate spin current such as spin Seebeck effect and spin pumping effect [2]. The conversion of charge current to spin current is known as spin Hall effect (SHE) and the inverse phenomenon is inverse SHE (ISHE). The detection of spin is usually realized by the ISHE. Spin Hall magnetoresistance (SMR) arises due to the simultaneous effect of SHE and ISHE in a bilayer heterostructures consisting of ferromagnetic (or ferrimagnetic) insulator (FMI) and a normal metal (NM). Magnetic Proximity Effect (MPE) observed in YIG/Pt complicates the spin transport scenario with additional effects such as Anomalous hall effect (AHE) which attenuate SMR signal.[4,5].Our group has successfully studied Ga: ZnO insertion on Bi: YIG/Pt and observed SMR signals, but the increase in spurious paramagnetic signal hampered the SMR signals with increasing Ga: ZnO thickness[6]. A solution for this is to employ antiferromagnetic moments, which are quite stable to stray fields and MPE. Recent studies in this direction has proved successfull in generating spin current using antiferromagnets NiO/Pt, Cr2O3/W, CuIr and SrMnO3/Pt layers. We have fabricated Antiferromagnetic oxide and metal oxide heterostructures through pulsed laser deposition and demonstrated generation of spin current through angle dependent magnetoresistance measurements (ADMR). The intereface induced magnetic anisotropy additionally contributes a four and six fold symmetry in ADMR measurements. This unsual interface induced symmetry and magnetoresistance effects in all oxide heterostructurs will be presented and discussed in detail. References 1. Matthias Althammer et. al., Phys. Rev. B 87, 224401 (2013). 2. T. Kikkawa et. al., Phys. Rev. Lett. 110, 067207 (2013). 3. E. Saitoh et. al., Appl. Phys. Lett. 88, 182509 (2006). 4. H. Nakayama et al., Phys. Rev. Lett. 110, 206601 (2013). 5. V. Castel et al., Appl. Phys. Lett. 101, 132414 (2012). 6. Matthias Althammer et.al.Appl. Phys. Lett. 110, 052403 (2017).

Resume : In the present era of “Internet-of-Things”, the demand for flexible, light-weight, low-cost, low-power consumption, multifunctional, and environmentally friendly electronics has moved to the forefront of materials science research. Numerous compounds with unique material properties in epitaxial thin film form hold key to future technologies. van der Waals epitaxy (vdWE) involving two-dimensional layered materials can play a crucial role in the expansion of thin film epitaxy by overcoming the bottleneck of material combinations due to lattice/thermal matching conditions inherent to conventional epitaxy. Among the layered materials, mica is a well-known phyllosilicate mineral that can have a remarkable impact on flexible electronics. We confine ourselves to the validity of vdWE of functional oxides on muscovite mica throughout this treatise. These heterostructures with excellent properties are flexible and exhibit high-temperature stability. With such demonstrations, it is anticipated that MICAtronics, vdWE on mica, can reveal unusual properties and emergent phenomena in the realm of high-performance flexible device applications.

Resume : Perovskites are well known for their wealth of functional properties. However, it is less known that perovskites also harbor materials with a room-temperature conductivity higher than platinum. The perovskite with the highest conductivity reported so far is SrMoO3. For oxide electronics, this opens the path to fully epitaxial perovskite based device stacks making use of the superior properties of epitaxial layers. Here, we show the use of SrMoO3 as bottom electrode in a high frequency agile device where the skin effect compels bottom electrodes with high micrometer thicknesses. Combining epitaxial growth of an extremely thick bottom electrode with an atomically controlled thin functional dielectric layer of (Ba,Sr)TiO3 on top is a huge challenge. We show how perovskites can overcome critical layer thicknesses and how a varactor device with unprecedented performance can be grown using all-oxide pulsed laser deposition.

Resume : Because of chemical stability, flexibility, tunable electrical conductivity, and possible integration on Si by epitaxy, perovskite oxides (ABO3) are great alternative to the main thermoelectric (TE) materials based on unstable scarce toxic tellurides. Indeed, n-type TE ABO3 such as transparent La-doped SrTiO3 (LSTO) can exhibit large TE power factor[1]. However, efficient p-type TE ABO3 still remains challenging. P-type transparent conducting Sr-doped LaCrO3 (SLCO) is appealing in this context[2]. After a brief reminder of n-type TE LSTO key results[1,3], we will present high-quality p-type TE SLCO films epitaxially grown on different oxide substrates (LAO, LSAT, STO and DSO) by molecular beam epitaxy (MBE)[4]. The films are flat and fully strained with low mosaicity (<0.1°). The impact of doping level, cationic stoichiometry (A/B) and epitaxial strain (ranging from -2.1% to +1.7%) on the structural and physical properties will be shown and discussed. In particular, optimized SLCO films can present relatively large Seebeck coefficient of about +180 μV/K with electrical resistivity around 1 Ωcm at room temperature. Finally, the integration of these films on Si has been done using a SrTiO3 epitaxial buffer layer with a view to building an integrated micro-thermoelectric module. [1] B. Jalan and S. Stemmer, Appl. Phys. Lett. 97, 042106 (2010) [2] K.H.L. Zhang et al., Adv. Mat. 27, 35 (2015) [3] M. Apreutesei et al., Sci. Tech. & Adv. Mat. 18, 430 (2017) [4] D. Han et al., submitted

Resume : Among the many kinds of flexible devices, self-powered electronic systems have attracted great interest because they allow for sustainable, long-lasting and remote use of the device without additional energy storage systems. Among them, flexible piezoelectric energy harvesting technology that converts mechanical energy into electric energy have attracted interest. Conventional plastic substrate harvesters showed the possibility of piezoelectric energy generation from repeated deformation and small bending deformation, but due to complicated manufacturing process and size limitations, complex process and size limitations result in the commercialization of piezoelectric self-driving technology. This study is based on a hybrid film of BaTiO3 and resin, and consists of a simple and easy inkjet process. The flexible, large-area piezoelectric hybrid film and Ag electrode layers are printed on flexible prints with only non-contact inkjet processes without high temperature annealing and complex transfer processes. The morphology of hybrid film was analyzed by SEM. The crystallinity of BaTiO3 was confirmed by XRD and Raman spectroscopy. And the All-inkjet-printed energy harvester converts periodically to mechanical deformations into voltage. Furthermore, it was confirmed that the output power increases as the all-inkjet-printed energy harvester is stacked.

Resume : In this work, ZnO/Cu/ZnO sandwich structure was fabricated as the transparent electrode on the flexible PET substrate. The sputtered ZnO/Cu/ZnO sandwich structure shows a low resistivity (5×10-4 Ω–cm) and high transmittance in the visible region (average around 82 %). To achieve the bendable and flexible properties, we co-sputtering Ti with the Cu metal layer (ZnO/Cu-Ti/ZnO) to enhance the toughness of the ZnO/Cu-Ti/ZnO sandwich structure. Our study shows that the resistivity of ZnO/Cu-Ti/ZnO (50/5/50 nm, 14.2 at.% Ti) is 6.29 × 10-4 Ω-cm and the average transmittance in the visible light region is above 80 %. Importantly, the ZnO/Cu-Ti/ZnO sandwich structure can withstand the reliability test at 85 °C and 85% humidity over 42 days. Also, the bending test shows that the flexibility of the sputtered ZnO/Cu-Ti/ZnO sandwich structure on the flexible PET substrate is greater than that of the sputtered ZnO/Cu/ZnO sandwich structure on the flexible PET substrate. The detail experimental results and discussion would be present in this talk.

Resume : VOx has been considered as an excellent candidate material for smart windows and solar cells due to its advantageous electronic properties. A plasma ion assisted electron beam evaporation process is used to deposit vanadium oxide on Si(100) substrates. We used different plasma discharge voltages, and currents at a constant working pressure to obtain new correlations between plasma parameters, such as ion velocity distributions, electron densities and presence and states of atomic and ionized species and material properties at the nanoscale. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy were employed to characterize the structure of the thin layers with a nominal thickness of 500 nm. The crystallinity, phase purity, as well as phase identity, vary greatly with discharge voltage. We typically observed in electron beam inconsistencies in oxygen gas flow lead to drastic variations of crystallinity and formation of defect layers throughout the sample bulk. The plasma was studied in-situ by optical emission spectroscopy, multipole resonance probe, and a retarding field energy analyzer during the deposition process. The combined data indicate correlations between the processing parameters and the resulting structure. Subsequently, optical properties and conductivity of samples were measured to access their performance for electrochemical applications.

Resume : Zinc oxide (ZnO) is used in the many applications such as tunnelling layer in solar cells or seed layers for ZnO nanorods. The Aluminium doped ZnO (AZO) films are used as transparent electrode in silicon based solar cells, where indium tin oxide (ITO) is too expensive. Unfortunately, higher resistivity at low thickness (< 200nm) and at low deposition temperatures (< 200°C) prevent wider utilization of AZO, especially in the field of flexible devices. On the contrary, high resistivity of ZnO seed layer is required to avoid external screening effect of ZnO nanorod-based piezogenerator. This work is focused on the possibility to optimize electrical properties of sputtered ZnO and AZO films by controlling of amount of incorporated oxygen at 100°C and 300°C. Oxygen rich conditions were simulated by deposition from ceramic target in Ar O2 atmosphere and oxygen poor conditions were simulated by the co-sputtering from metallic and ceramic target. The relations between oxygen conditions and electrical and optical properties were investigated in detail. The changes were explained by means of dominant internal defects at the the different oxygen conditions during the processing. The control of amount of incorporated oxygen allows to adjust the ZnO film for different applications and to achieve higher carrier concentration of AZO and thus increase the usability as a transparent electrode on the flexible substrates.

Resume : This work aims to develop the growth of functional oxides on low-cost substrates and to propose a new solution for the integration of high quality complex oxides with multifunctional properties for large surface electronics. This integration is often obtained by epitaxial growth of oxides on relatively expensive single-crystalline substrates, which offer a limited choice of materials and crystallographic orientations. The project focuses on the replacement of these single crystalline substrates by quite low-cost (as widely used silicon) or amorphous (as glass) substrates, covered by a crystalline template of molecular thickness (oxide nanosheets), that can be used as seed layers to induce epitaxy of complex oxides thin films on the bottom substrate material. The presentation will be focused on Ca2Nb3O10- nanosheets, obtained by protonation and exfoliation of KCa2Nb3O10 lamellar oxide previously synthetized by solid state reaction and by molten salts reaction. The transfer on Si (100) and SiO2 substrates is performed by Langmuir-Blodgett process. Atomic Force Microscopy shows a smooth covering of the surface. KNbO3 (KNO) and BiFeO3 (BFO) films were then deposited on these nanosheets seed layers by pulsed laser deposition and chemical solution deposition, respectively. Their structural properties were investigated in details. X-ray diffraction measurements show (100) oriented pure BFO and KNO films, which demonstrate the promising utility of nanosheets for epitaxial growth.

Resume : As a potential material for oxide dielectrics, yttrium oxide (Y2O3) is getting more and more attention because of its excellent thermal and electronic properties, such as high dielectric constant (14~20) and large refractive index (1.7~2.0). Usually, the high deposition temperature and/or vacuum are/is necessary for preparing high quality Y2O3. These strict growth conditions increase the fabrication cost and restrict the commercial applications of Y2O3. So, how to simplify the growth conditions while maintaining the high quality is the key to large-scale application of Y2O3 films. In our work, we prepared Y2O3 thin films at low growth temperature (400 °C) under atmospheric pressure using 3rd generation mist CVD with two solution chambers and one mixing chamber, which can supply the active materials without reactions before arriving the reactor and is an equilibrium reaction system with environmentally friendly and cost-effective characteristics. Experimentally, we obtained the YOx films with deposition rate of 9.0 nm/min, refractive index of 1.74 and dielectric constant of 15~20 under the conditions of yttrium precursor dissolved in MeOH and H2O supported the fabrication. In addition to investigating the effects of oxygen source on the fabrication of YOx films, we also studied the mechanisms of obtaining high quality thin films at low growth temperature. The details about fabrication of high quality Y2O3 thin films by 3rd generation mist CVD will be presented in the conference.

Resume : Amorphous HfO2 is the most used high-k gate dielectric materials for reducing the tunneling leakage current and improving the reliability to overcome the physical limitation of SiO2. However, the electrical properties of HfO2-based devices can be affected by heavy ion irradiation in the space environment. In this study, the amorphous HfO2 films transformed to a monoclinic crystal structure induced by swift heavy ions (SHIs) irradiation was observed directly. The dielectric properties of HfO2 thin films get more deteriorated with increasing ion fluences and electronic energy loss ((dE/dx)e) due to crystallization. Furthermore, the threshold of the ((dE/dx)e) for crystallization is about 10 keV/nm deduced by fitting the relationship between the area of latent track and ((dE/dx)e). The quantitative relationship between microstructures and dielectric properties allows for prediction of device sensitivity to heavy ion irradiation and provides a new method to estimate the threshold of the ((dE/dx)e) for crystallization.

Resume : Indium-tin oxide (ITO) is a widely used transparent conductor which finds application in every day electronics such as touch screens and light emitting diodes. One key limitation of ITO is the brittle nature of this ceramic, that arises due to its typical thickness exceeding 10 nm, prohibiting its use in flexible electronics. Herein we report the wafer scale synthesis of highly flexible two-dimensional (2D) ITO nanosheets with a typical thickness of 1 nm. We apply a low temperature liquid metal printing approach that can be utilized to directly deposit 2D ITO onto a desired substrate. The final nanosheets feature two orders of magnitude lower light absorption when compared with graphene, while maintaining high electrical conductance. The 2D ITO, when deposited onto polymer sheets, could be bend to a radius of 2 mm without performance degradation after 1000 bending cycles. Finally, centimeter sized 2D ITO sheets could be synthesized on transparent substrates and fully functional capacitive touch screens were fabricated. The developed technique may enable low cost, printed and flexible optoelectronics, while also providing an alternative to graphene with superior transparency for the creation of van der Waals heterostructures.

Resume : Due to increasing energy demands and growing interest in alternative energy production possibilities, various oxides have come into research focus as functional materials in , for example, solar cells or energy storage. However, not only the material itself but also its synthesis procedure should fit the aim of green energy, for example by being energy saving and environmental friendly. A deep understanding of the influence of the deposition process on the quality of the film is crucial. In this work, we present the electron microscopic investigation of a VOx film on Si substrate, deposited by a plasma ion assisted process. The process was monitored in-situ which allows to draw correlations between deposition parameters and film properties. The as-deposited film appears to be X-ray amorphous but cross-sectional transmission electron microscopy (TEM) shows highly crystalline bands inside the otherwise amorphous VOx film. The crystalline bands can be ascribed to variations in the plasma parameters during deposition. In-depth electron diffraction experiments and electron energy-loss spectroscopic (EELS) analysis in TEM indicate the crystalline bands are γ-V2O5, which is the distorted version of orthorhombic α-V2O5. In the amorphous part of the film the atomic arrangement of the nearest neighbor is comparable to the one in γ-V2O5, leading to a similar fingerprint in the EELS data. Combining this insight with the in-situ monitored plasma parameters the deposition process can be tuned for targeted patterning of (VOx) thin films.

Resume : Pulsed laser deposition (PLD) has become a very popular technique for experimental studies and has proven itself as a distinctive tool for the manipulation of thin film growth. Nowadays PLD is being considered as a potential production tool to face the challenges in thin film synthesis related to upcoming technology nodes in CMOS manufacturing. New and complex metal oxide thin films and devices are required as computing power according to Moore’s law is no longer being met by scaling alone. The intrinsic differences and unique features of PLD position it as a powerful and complementary tool among the other deposition techniques for advanced thin film growth. These days PLD has matured into commercial equipment enabling application development and pilot production in niche markets. Improved PLD equipment is required to meet the stringent specifications for mass production of oxide nano-electronics. The hardware development is ongoing, and the availability is expected within 5 years. This contribution will describe the current state-of-the -art of PLD for large area deposition and will outline the scalability towards volume manufacturing. Different PLD thin film application development cases for commercial products will be discussed.

Resume : Plasma-enhanced atomic layer deposition (ALD) of metal oxides is a rapidly gaining interest especially in the electronics industry because of its numerous advantages over the thermal process. However, the underlying reaction mechanism is not sufficiently understood, particularly regarding saturation of the reaction and densification of the film. In this work, we employ first principles density functional theory (DFT) to determine the predominant reaction pathways, surface intermediates and by-products formed when constituents of O2-plasma or O3 adsorb onto a methylated surface typical of TMA-based alumina ALD. The main outcomes are that a wide variety of barrierless and highly exothermic reactions can take place. This leads to the spontaneous production of various by-products with low desorption energies and also of surface intermediates from the incomplete combustion of ?CH3 ligands. Surface hydroxyl groups are the most frequently observed intermediate and are formed as a consequence of the conservation of atoms and charge when methyl ligands are initially oxidized (rather than from subsequent re-adsorption of molecular water). Anionic intermediates such as formates are also commonly observed at the surface in the simulations. Formaldehyde, CH2O, is the most frequently observed gaseous by-product. Desorption of this by-product leads to saturation of the redox reaction at the level of two singlet oxygen atoms per CH3 group, where the oxidation state of C is zero, rather than further reaction with oxygen to higher oxidation states. We conclude that the self-limiting chemistry that defines ALD comes about in this case through the desorption by-products with partially-oxidised carbon. The simulations also show that densification occurs when ligands are removed or oxidised to intermediates, indicating that there may be an inverse relationship between Al/O coordination numbers in the final film and the concentration of chemically-bound ligands or intermediate fragments covering the surface during each ALD pulse. Therefore reactions that generate a bare surface Al will produce denser films in metal oxide ALD.

Resume : The present work focuses on the deposition, doping and heat treatment of Ga2O3 films with atomic layer deposition (ALD). ALD is a self-limiting layer by layer growth method based on the consecutive chemisorption of precursor gases on a heated substrate surface resulting in a uniform and conformal coverage and a mono-layer by mono-layer growth even on high aspect ratio or nanostructured surfaces. Ga2O3 is a wide band-gap semiconductor very promising due to its photocatalitic properties, gas sensing properties as well as its possible applications as UV transparent conductive oxide, but the lack of a reliable p-dopant hinders its use in photonics. One way to achieve p-type doping may be Zn doping. The present work uses a novel Ga precursor, hexakis-dimethylamino-digallium, which facilitates the use of a wider ALD window than the commonly used precursors (between 130°C and 270°C). The Zn doping was performed using diethylzinc, and water was used as an oxidant. As ALD deposited Ga2O3 films are always amorphous, a number of different heat treatments were used to achieve crystalline β- Ga2O3. The films were deposited with a Picosun Sunale R-100 reactor, the morphology of the layers was characterised with atomic force microscopy, the crystal structure and orientation were examined by X-ray diffraction, transmission measurements were conducted. The bandgaps and dielectric properties of the layers were determined using ellipsometry, and the breakdown voltages were determined.

Resume : Optics plays a crucial role in the field of devices and sensors including optical devices which can be considered as the building blocks of optical systems, networks and interconnects. Optics has also gained advantages in the area of information processing utilizing external Electro-optic (EO) modulators having fast response time and are realizable in either reflection or transmission geometry. Among the known ferroelectric EO materials, lead free Strontium Barium Niobate (Sr_x Ba_(1-x) Nb_2 O_6, SBN) possess highest electro-optic coefficient, pyroelectric coefficient and photorefractive properties. The present work reports about the growth of SBN thin films on fused silica substrate utilizing Pulsed Laser Deposition (PLD) technique by varying the laser fluence. The growth was carried out at a fixed ambient oxygen pressure and temperature with the repetition rate of 10Hz of the laser. The structural and morphological properties of the films were examined indicating the substantial use of films for EO modulators. Raman and UV -Visible spectroscopy were utilized to determine the band gap and raman active modes of the SBN thin films. Complex dielectric constant and refractive index of the SBN thin films as a function of laser fluence has been obtained utilizing SPR tool. The EO properties of the prepared SBN thin films has been also investigated utilizing a simplistic approach of Senarmont compensator. The effective birefringence and the EO coefficient as a function of applied electric field was also estimated.

Resume : The superconducting properties of YBa2Cu3O7-d (YBCO) films may be significantly improved through the introduction of nanosized defects. In this work, two new strategies for nano-doped YBCO Chemical Solution Deposition (CSD) are proposed and compared. The first study is focused on Nanodiamond (ND) introduction in YBCO films. This doping strategy has never been reported until our recent preliminary study [1] that showed ND potential for the improvement of YBCO transport properties. Further optimizations of the YBCO-ND CSD process have been accomplished and results are illustrated. Moreover, a second doping option has been evaluated using Gd for the introduction of effective defects. Many studies have been already carried out in the last decade on the replacement of Y3+ in YBCO by other rare earth elements such as Gd3+ to form Y1-xGdxBa2Cu3O7-d mixed compounds. However, the use of Gd added in excess with respect to YBCO has never been studied and is proposed in the present work. YBCO films with ND and Gd addition (YBCO-ND and YBCO-Gd) have been deposited with low-fluorine CSD route on (100) SrTiO3 single crystal. The samples have been characterized via SEM, XRD, VSM, dc resistivity and critical current measurements. Good epitaxial films have been obtained in both cases, and a significant improvement of film morphology and superconducting properties has been observed with respect to pure YBCO. Dopants seem to have beneficial effect on YBCO morphology. Both YBCO-ND and YBCO-Gd films generally show denser, smoother and more connected surfaces. The good morphology corresponds to increased superconducting properties. Higher zero-field critical current densities have been measured in the temperature range from 10 K to 77 K (i.e. 18 and 28 MA/cm2 respectively for YBCO-ND and YBCO-Gd in comparison with 13± 0.1 MA/cm2 of pure YBCO at 10 K). Those results could be mainly ascribed to an improvement of percolation path due to the increase of film density and grain coalescence. However, some differences on the in-field behavior and temperature dependence of transport properties can be observed, evidencing a different role of ND with respect to Gd on YBCO nucleation and growth. [1] V. Pinto, et al .IEEE Trans. Appl. Supercond. 28, (2018) 7500704. DOI: 10.1109/TASC.2018.2800765

Resume : Achieving low cost, safe, reproducible, and high performance superconducting thin films of YBa2Cu3O7−δ is essential to bring this material to the energy market. Here, we report on the chemical solution deposition of YBa2Cu3O7−δ nanocomposites from environmentally benign precursors with a low fluorine content. Preformed ZrO2 nanocrystals (3.5 nm) were stabilized in a methanolic precursor solution via two strategies: charge stabilization and steric stabilization. Counterintuitively, charge stabilization did not result in high quality superconducting layers, while the steric stabilization resulted in highly reproducible nanocomposite thin films with a self-field Jc of 4−5 MA cm−2 (77 K) and a much smaller decay of Jc with magnetic field compared to YBa2Cu3O7−δ without nanocrystals. In addition, these nanocomposite films show a strong pinning force enhancement and a reduced Jc anisotropy compared to undoped YBa2Cu3O7−δ films. Given the relationship between the nanocrystal surface chemistry and final nanocomposite performance, we expect these results to be also relevant for other nanocomposite research. Reference: H. Rijckaert, et al., "Optimizing Nanocomposites through Nanocrystal Surface Chemistry: Superconducting YBa2Cu3O7 Thin Films via Low-Fluorine Metal Organic Deposition and Preformed Metal Oxide Nanocrystals," Chem. Mater., 29 [14] 6104-13 (2017).

Resume : Aerosol impaction is a dry spray technique, that when coupled with plasma synthesis of nanoparticles, has the ability to create oxide films of customizable thickness and porosity. We demonstrate the use of our Aerosol Impaction-Driven Assembly (AIDA) system for silica films ranging in thickness from 50 nm – 1 mm, with tunable porosity from 10 – 90%. The ability to manipulate these film properties has generated unique multifunctionality. Through a broad available range in refractive index, our coatings have demonstrated use as antireflective coatings for solar cell applications as well as transparent thermal insulation for windows. Our silica films are composed of 4-6 nm spherical particles, generated from gaseous or liquid precursors through a low pressure dusty plasma synthesis. Film thickness is characterized using ellipsometry or electron microscopy. Porosity is determined using ellipsometry or Brunauer-Emmett-Teller (BET) techniques. Coating durability, thermal conductivity, modeling (thermal, mechanical), and optical properties are also extensively examined where applicable. With resultant films yielding <5% nonuniformity, this novel technique provides reliable coatings for a wide range of applications.