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INFORMATION AND COMMUNICATION TECHNOLOGIES

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Ion-related phenomena in nanoscale oxide systems: from fundamentals to applications

Local ionic effects in oxide systems are emerging as a pivotal aspect in nanoionics, iontronics, catalysis and energy storage. This symposium focuses on the recent advances in understanding and controlling nanoscale ionic effects, and on their application in novel solid-state microdevices.

Scope:

Functional oxide systems are at the basis of a whole new-generation of miniaturized solid-state devices for electronics, energy conversion and energy storage. In these systems, the role of ionic structure and defects (dopant element distribution, dislocations, grain boundaries, interfaces and surfaces) and the local interaction between ionic and electronic species play a pivotal role and can become predominant over the expected bulk behavior. These nanoionic effects may lead to the improvement of existing functionalities or even to the emergence of novel states, that can be harvested for application. The possibility of fabricating layered heterostructures and “interface-dominated” materials as well as of controlling nanoscale phenomena and dimensionality is key for a rational use of such materials in technology.

This symposium is aimed to bridge the fundamentals of oxide local structures with device fabrication and oxide implementation into real devices. It will provide a forum for discussion on oxide physics and chemistry, including surface activity, space-charge effects, local non-stoichiometry, strain, high electron and ion mobility states, and mass transport at the interfaces. Furthermore, it will focus on the practical utilization of such effects for several applications including solid oxide fuel cells, memories and neuromorphic devices, gas sensors, electrolyzers and microbatteries. Attention will be put on state-of-the-art techniques for thin-film fabrication such as PLD, sputtering, ALD, MBE and on strategies for their scalability such as large area deposition, epitaxy on Si and film transfer onto technological supports. Advances on microscopy, spectroscopy and electrical methods for local characterization will be discussed.

Hot topics to be covered by the symposium

  • Local electrical transport engineering: space-charge, local non-stoichiometry, strain, high-dimensional defects, etc.
  • Mass and charge transport at interfaces and surfaces
  • Ion-driven electronic effects
  • Interface-dominated architectures: grain boundaries, dislocations, multilayers
  • Interface investigation techniques
  • Advances in fabrication methodologies for thin-films
  • Light-driven ionic phenomena
  • Memristive devices and neuromorphics
  • Water and oxygen reactivity based on oxides/ionic configuration
  • Micro solid state devices: fuel cells, memristors, batteries, thin-film transistors, etc.

List of invited speakers (confirmed):

  • Guus Rijnders (University of Twente, NL)
  • Scott Chambers (Pacific Northwest National Laboratory, USA)
  • Vesna Srot (Max Planck Institute, DE)
  • Ainara Aguadero (Imperial College, UK)
  • Albert Tarancon (ICREA, ES)
  • Markus Kubicek (Technical University Wien, AT)
  • Vincenzo Esposito (Technical University of Denmark, DK)
  • Mark Huijben (University of Twente, NL)
  • Christoph Bäumer (Stanford University, USA) 
  • Martin Setvin (Technical University Wien, AT)
  • Monica Burriel (LMGP Grenoble, FR)
  • David Muñoz-Rojas (Grenoble INP, FR)
  • Nejc Hodnik (National Institute of Chemistry, SI)
  • Agham Posadas (University of Texas at Austin, USA)
  • Christian Jooss (University of Göttingen)

List of scientific committee members:

  • Iñigo Garbayo (CIC Energigune, ES)
  • Jose Santiso (ICNM2, ES)
  • Rainer Waser (RWTH Aachen University, DE)
  • Judith MacManus-Driscoll (University of Cambridge, UK)
  • Regina Dittmann (Forschungszentrum Jülich, DE)

The symposium will host a special session “Harvestore - Heat and light for powering the Internet of Things” in which a selection of invited and contributed speakers will focus on the latest advances in the fields of energy harvesting and of micro-devices.

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08:50 Welcome remarks    
 
Nanoscale characterization : Session chair Nejc Hodnik
09:00
Authors : Vesna Srot1, Yi Wang1, Matteo Minola1, Ute Salzberger1, Bernhard Fenk1, Marion Kelsch1, Marco Salluzzo2,3, Gabriella Maria De Luca3,2, Bernhard Keimer1 and Peter A. van Aken1
Affiliations : 1. Max Planck Institute for Solid State Research, Stuttgart, Germany 2. CNR-SPIN Napoli Complesso Monte Sant´ Angelo via Cinthia, Napoli, Italy 3. Dipartimento di Fisica ``E. Pancini`` Complesso Monte Sant´ Angelo via Cinthia, Napoli, Italy

Resume : With the latest technological progress and methodological developments in scanning transmission electron microscopy (STEM) fascinating phenomena have been revealed at the atomic scale in functional complex oxides. Simultaneous acquisition of high-angle annular dark-field (HAADF-) and annular bright-field (ABF-) STEM images opened up an efficient way for combined imaging of light and heavy elements. High-quality NdBa2Cu3O7 (NBCO) ultra-thin films have been deposited on TiO2-terminated SrTiO3 (STO) substrates by high oxygen pressure diode sputtering. The stacking sequence along the growth direction parallel to the c-axis of NBCO is BaO-CuO2-Nd-CuO2-BaO-CuO. In NBCO, Cu atoms are located in CuO2 planes and in parallel CuO chains. Physical properties of NBCO can be drastically influenced due to oxygen content fluctuations, where the charge balance between the planes and the chains strongly affects and dictates Tc [1]. We have applied atomically resolved quantitative analytical STEM imaging combined with extensive STEM image simulations to investigate the local cation and anion sub-lattices and their distortions, as well as the chemical identity of NBCO films and NBCO/STO interfaces [2]. In addition, surface steps on the STO substrate dictate the defects in NBCO films and will be discussed in detail. [1] RJ Cava et al., Physica C 165 (1990) 419. [2] V Srot et al., Microscopy and Microanalysis 24 (2018) 76.

A.1.1
09:30
Authors : Martin Setvin
Affiliations : TU Wien, Institute of Applied Physics, Wiedner Hauptstrasse 8-10/134

Resume : Recent development of the noncontact atomic force microscopy (nc-AFM) has opened new possibilities in different fields ? imaging of organic molecules [1], controlling the charge state of adsorbed species [2], or enhanced chemical resolution of surface atoms [3]. The emerging possibilities and opportunities in the field of oxide surfaces and their surface chemistry will be outlined in this contribution. The limits of atomic resolution will be illustrated on binary oxides like TiO2, In2O3. The enhanced chemical resolution of nc-AFM offers a unique opportunity for approaching complex materials with ternary chemical composition: In particular, we have succeeded in imaging bulk-terminated (001) surfaces of SrTiO3 and KTaO3 perovskites. A dedicated cleaving procedure [4,5] allows preparing flat regions terminated by domains of SrO/TiO2 (or KO/TaO2) with a well-defined, bulk-like atomic structure. The stability, point defects, electronic structure, and chemical properties of these surfaces will be discussed and linked to the incipient-ferroelectric character of these materials. [1] Gross, L.; Mohn, F.; Moll, N.; Liljeroth, P.; Meyer, G., Science 2009, 325, 1110 [2] Gross, L.; Mohn, F.; Liljeroth, P.; Repp, J.; Giessibl, F. J.; Meyer, G., Science 2009, 324, 1428 [3] Sugimoto, Y.; Pou, P.; Abe, M.; Jelinek, P.; Perez, R.; Morita, S.; Custance, O., Nature 2007, 446, 64 [4] I. Sokolovic, M. Schmid, U. Diebold, M. Setvin, Phys. Rev. Materials 3, 034407 (2019) [5] M. Setvin, M. Reticcioli, F. Poelzleitner, J. Hulva, M. Schmid, L. A. Boatner, C. Franchini, U. Diebold, Science 359, 572-575 (2018)

A.1.2
10:00
Authors : Matthieu Bugnet (1), Quentin M. Ramasse (2,3), Marcel Hennes (4), Xiaorong Weng (4), Dominique Demaille (4), Benoît Gobaut (5), Amélie Juhin (6), Philippe Sainctavit (6), Yunlin Zheng (4), Franck Vidal (4), Guillaume Radtke (6)
Affiliations : (1) Univ Lyon, INSA Lyon, UCBL Lyon1, MATEIS, CNRS UMR 5510, F-69621 Villeurbanne, France; (2) SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, United Kingdom (3) School of Physics and School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom; (4) Sorbonne Université, CNRS, INSP, 75005 Paris, France; (5) Synchrotron Soleil, L?Orme des Merisiers Saint-Aubin BP 48, 91192 Gif-sur-Yvette Cedex, France; (6) Sorbonne Université, CNRS, IMPMC, 75005 Paris, France;

Resume : The growth of 3D spintronic structures, such as self-assembled ferromagnetic nanowires (NWs) embedded in an insulating matrix (e.g. Ni in SrTiO3 (STO)), has been proposed as a promising route to overcome the limits of current data storage technologies. This interest is mainly motivated by the possibility to tune the magnetic anisotropy either through the control of the chemical composition of the NWs or through the presence of interfacially-induced strain giving rise to magneto-elastic anisotropy. The detection of Ni oxidation, which would be highly detrimental, is of interest and remains a challenge. This is achieved by investigating the Ni-L23, O-K and Ti-L23 fine structures from the matrix to the Ni:STO interface. Here, the local chemistry of the Ni:STO interface is probed at the atomic scale in the monochromated aberration-corrected scanning transmission electron microscope (STEM). Electron energy-loss spectroscopy (EELS) investigations of the structurally abrupt Ni:STO interface indicate the presence of a weak interdiffusion over a few atomic planes only. This leads essentially to a metallization of the last TiOx (x < 2) atomic plane of the matrix, and to the formation of non-stoichiometric mixed Ni-Ti oxide on the external part of the NW. These results demonstrate the absence of Ni oxidation, confirmed by x-ray absorption spectroscopy, and highlight that Ni:STO is a model system for strain engineering of the magnetic anisotropy in vertically aligned nanocomposites.

A.1.3
10:15
Authors : A. Barbier (1), B. Sarpi (2), P.-L. Nguyen (1), M. Rioult (1,2), T. Aghavnian (1,2), D. Stanescu (1), J.-B. Moussy (1), C. Rountree (1), H. Magnan (1), F.Maccherozzi (3), N. Jedrecy (4), R. Belkhou (2)
Affiliations : (1) Service de Physique de l'Etat Condensé, Gif-sur-Yvette, France ; (2) Synchrotron SOLEIL, L'Orme des Merisiers Saint-Aubin, France ; (3) Diamond Light Source, Oxforshire, United Kingdom (4) INSP, UPMC-Sorbonne Universités, 75252 Paris Cedex 05, France

Resume : Multiferroic materials are of current technological interest. They are expected to become key components of new devices in important technological fields like spintronics, sensors, multiple state memory cells, energy harvesting etc. Within this framework, magneto-electric multifunctional multiferroics having simultaneous ferromagnetic and ferroelectric long range orderings are particularly relevant. Artificial multiferroics obtained by combining ferroelectric and ferromagnetic materials are a seductive route to overcome the lack of intrinsic single phase multiferroics. We considered nanometric combinations of epitaxial thin films of BaTiO3, which is the prototypical ferroelectric material, and ferrimagnetic ferrites over-layers (NiFe2O4, MnFe2O4 and CoFe2O4), which are respectively low, moderately and highly magnetostrictive oxides. These combinations are of practical interest since all ordering temperatures are above room temperature and the compounds are fully oxidized and highly stable. All films were elaborated by atomic oxygen plasma assisted molecular beam epitaxy in conditions providing high quality single crystalline stacks. The layers were electrically polarized by using local pattern writing with Piezo-Force Microscopy (PFM) and we studied the ferroelectric, chemical and magnetic responses of the individual layers thanks by synchrotron radiation X-ray spectromicroscopy (XPEEM) exploiting photon energy and light polarization tuning. For all systems, electrical local polarization revealed specific spectroscopic responses evidencing chemical reduction and likely ion migration. Our observations show that the chemical, morphologic, magnetic and ferroelectric contributions are highly entangled.

A.1.4
10:30 Coffee break    
 
Defect chemistry I: Defect-property relations : Session chair Scott Chambers
11:00
Authors : Christoph Baeumer, Tyler Mefford, Qiyang Lu, Slavomír Nemsák, Regina Dittmann, Rainer Waser, William C. Chueh
Affiliations : Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA; Institute of Electronic Materials (IWE2), & JARA-FIT, RWTH Aachen University, Aachen, Germany; Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Peter Gruenberg Institute (PGI7) & JARA-FIT, Forschungszentrum Juelich GmbH, Juelich, Germany

Resume : Energy storage through the electrocatalytic generation of chemical fuels such as hydrogen is an attractive pathway for storing intermittent renewable energies. However, the high overpotentials resulting from the slow kinetics of the oxygen evolution reaction (OER) must be overcome, requiring a detailed understanding of the underlying relationships between catalytic activity, stability and atomic-level surface structure. Such an understanding has proven challenging to obtain due to the practical difficulties in controlling surface areas and structures during study. To overcome this limitation, we employ single crystalline model systems: Thin, epitaxial perovskite films are used as electrocatalysts for the OER, providing a versatile and atomically defined platform for the investigation of activity and stability trends. We focus our study on LaNiO3, because it was predicted to possess one of the highest catalytic activities of all ternary oxides yet reported activities for polycrystalline samples vary significantly. As even nominally single crystalline surfaces may undergo chemical and structural changes due to dissolution processes and self-(re)assembly under OER conditions, we study these model catalysts using a diverse suite of advanced in situ and ex situ analysis techniques for structural, morphological, electronic and chemical understanding of the processes occurring under OER conditions. We find that the surface chemistry and morphology of LaNiO3 critically depend on the fabrication temperature, resulting in selectively tunable Ni redox chemistry and OER activity. These findings underline the importance of well-defined surface structures and chemistries for catalyst design.

A.2.1
11:30
Authors : Maximilian F. Hoedl [a], Tor S. Bjorheim [b], Rotraut Merkle [a], Eugene A. Kotomin [a], Joachim Maier [a]
Affiliations : [a] Max Planck Institute for Solid State Research, Heisenbergstr. 1, D-70569, Stuttgart, Germany [b] University of Oslo, Gaustadalléen 21, 0349 Oslo, Norway

Resume : Oxides can dissociatively incorporate water into oxygen vacancies, but the thermodynamic feasibility of this reaction varies greatly. The individual contributions from proton affinity of lattice oxide ions and hydroxide affinity of oxygen vacancies to the hydration enthalpy are experimentally not accessible. This impedes an in-depth understanding of the hydration trends for different materials. We present a thermochemical cycle involving first-principles calculations that allows for the calculation of proton and hydroxide affinities, and apply this scheme to a large variety of oxides ranging from binary oxides, e.g. Cs2O to SiO2, to ternary oxides, e.g. BaZrO3. Band alignment with respect to vacuum ensures the comparability of the calculated ion affinities.[1] Although they describe purely ionic reactions, the proton and hydroxide affinities correlate with the oxide?s electronic structure, in particular with the ionization potential (position of O2p states relative to vacuum). The variation is more pronounced for the proton affinity, naturally explaining the often found phenomenological trend between basicity of the oxide and more favorable hydration.[1] Having established a general understanding of the interplay between the oxide?s electronic structure and the thermodynamics of water incorporation, we proceed to open-shell proton and electron conducting perovskites (e.g. cathode materials). [1] T.S. Bjorheim, M.F. Hoedl, R. Merkle, E.A. Kotomin, J. Maier, to be submitted

A.2.2
11:45
Authors : M. Tyunina 1,2,*, J. Peräntie 1, T. Kocourek 2, S. Saukko 3, H. Jantunen 1, M. Jelinek 2, A. Dejneka 2
Affiliations : 1 Microelectronics Research Unit, Univeristy of Oulu, Finland; 2 Institute of Physics of the Czech Academy of Sciences, Prague, Czechia; 3 Center of Microscopy and Nanotechnology Univeristy of Oulu, Finland

Resume : Large out-of-plane electrical polarization, which is perpendicular to free surface of electrodeless perovskite oxide ferroelectrics, can enable advanced applications in solar water splitting, artificial photosynthesis, catalysis, and cell biology. However, due to natural coexistence of ferroelectric domains with different orientations of polarization, the desired polarization is difficult to obtain without electrical poling and electrodes. Here, we demonstrate out-of-plane self-polarization of 0.2 C/m2, which is achieved by defect engineering in thin films of environmentally friendly ferroelectric barium titanate. The films are prepared by pulsed laser deposition. The self-polarized epitaxial films are grown using reduced oxygen pressure during deposition. Another necessary condition is the presence of large biaxial in-plane compressive misfit strain. The films? crystal and electronic structures and electrical responses are analyzed by several complementary techniques. It is shown that the in-built field and self-polarization originate from the formation and ordering of dipolar defect complexes. The complexes comprise charged oxygen vacancies and trivalent titanium cations. It is argued that the peculiar defects? configuration is caused by lattice strain.

A.2.3
12:00
Authors : R.I. Eglitis, J. Purans and J. Gabrusenoks
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063, Latvia

Resume : We have performed ab initio calculations for the F-center in the BaTiO3 and SrZrO3 bulk and on the BaO-terminated and ZrO2-terminated (001) surface using a supercell model and a hybrid B3PW exchange-correlation functional [1,2]. We find that two Ti atoms nearest to the bulk F-center in BaTiO3 are repulsed, while nearest eight oxygen and four barium atoms relax towards the oxygen vacancy (by 1.06, 0.71 and 0.08% of the lattice constant a0, respectively). The magnitudes of atomic displacements around the F-center located on the BaO-terminated (001) surface in most cases (except for Ti) are larger than those around the bulk F-center (0.1, 1.4 and 1.0% of a0, respectively). The bulk and BaO-terminated (001) surface F-center bands in BaTiO3 matrix are located only 0.23 and 0.07 eV under the conduction band (CB) bottom, indicating that the F-center is a shallow donor. The F-center in the BaTiO3 bulk contains charge of 1.103e, whereas slightly less charge, only 1.052e, are localized inside the F-center on the BaO-terminated (001) surface. Our calculations demonstrate considerable increase of the chemical bond covalency between the BaTiO3 bulk F-center and its two nearest Ti atoms equal to 0.320e, and even larger increase for BaO-terminated (001) surface F-center and its nearest Ti atom 0.480e, in comparison to the relevant Ti-O chemical bond covalency in the perfect BaTiO3 bulk 0.100e. The difference between F-center formation energy in BaTiO3 bulk (10.3 eV) and on the BaO-terminated (001) surface (10.2 eV) trigger the segregation of the F-center from the bulk towards the BaO-terminated (001) surface. We also performed ab initio calculations for BaTiO3/SrTiO3 and PbZrO3/SrZrO3 (001) interfaces as well as WO3 polar (001) surfaces [3]. For BTO/STO and PZO/SZO (001) heterostructures, we found that the number of interface layers do not influence much the electronic structure of studied structures, while termination of deposited BTO and PZO (001) thin film atop of STO and SZO substrates considerably shift the band edges with respect to the vacuum level and thus reduce the band gap. References: 1. R.I. Eglitis, S. Piskunov, Comput. Condens. Matter 7, 1-6 (2016) 2. M. Sokolov, R.I. Eglitis, S. Piskunov, Y.F. Zhukovskii, Int. J. Mod. Phys. B 31, 1750251 (2017) 3. S. Piskunov, R.I. Eglitis, Solid State Ionics 274, 29-33 (2015)

A.2.4
12:15
Authors : Oliver Diwald1, Matthias Niedermaier1,Thomas Schwab1, Paolo Dolcet2,3, Silvia Gross2, Johannes Bernardi4, Michel Bockstedte1;
Affiliations : 1: Department of Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Strasse 2a, A-5020, Salzburg, Austria; 2:Università degli Studi di Padova, Dipartimento di Scienze Chimiche, and INSTM, UdR Padova, via Marzolo 1, I-35131, Padova, Italy; 3: Karlsruher Institut für Technologie (KIT), Institut für Technische Chemie und Polymerchemie (ITCP), Engesserstr. 20, 76131 Karlsruhe, Germany; 4: University Service Center for Transmission Electron Microscopy, Technische Universität Wien, Wiedner Hauptstrasse 8-10, A-1040, Vienna, Austria;

Resume : Stability and functional properties of doped nanoscale metal oxides are determined by defect chemistry and interfaces. For vapor phase grown non-equilibrium solids, ion diffusion provides efficient means to adjust the functional properties of the material. Insights into the underlying transformation process are essential for both nanomaterial design and material applications at elevated temperatures. In the present contribution we will discuss the transformation behaviour of diluted transition metals (e.g. Fe, Co) in MgO nanocrystals, which were prepared by metallocene injection into a metal combustion flame. Vacuum annealing provides means to control impurity localization and to trigger phase separation in these non-equilibrium solids.[1] By combining structure characterization with X-ray absorption and X-ray photoelectron spectroscopy investigations, we tracked valence state and local chemical environment changes of transition metal ions inside the nanoparticles. For Fe-Mg-O nanoparticles we obtained evidence for the formation of impurity-Mg vacancy complexes which ultimately undergo surface migration to enable magnesioferrite nucleation.[2] Differences in the behaviour between Co and Fe impurities will be discussed and rationalized by means of ab initio calculations. [1] A. R. Gheisi, Part. Part. Syst. Char. 2017, 34, 1700109. [2] M. Niedermaier, J. Phys. Chem. C 2017, 121, 24292.

A.2.5
12:30 Lunch break    
 
Catalysis and electrode activity : Session chair: Albert Tarancon
14:00
Authors : Christian Jooss1, Gaurav Lole1, Emanuel Ronge1, Jonas Lindner1, Daniel Mierwaldt1 and Marcel Risch1,2 and Vladimir Roddatis1
Affiliations : 1 Insitute of Materials Physics, University of Goettingen, Germany 2 Helmholtz Zentrum für Materialien und Energie, Berlin

Resume : Oxide electrodes can form highly dynamic surface states during the oxygen evolution reaction. Understanding the transition from reversible adatom dynamics to irreversible defect chemical reactions is essential for understanding catalyst activity and stability. We present environmental Transmission Electron Microscopy (ETEM) studies of different manganese oxide electrodes in H2O at positive electric potentials, involving manganite perovskites, Ruddlesden-Popper phases and birnessites. Depending on the atomic and electronic structure of the studied systems, a quite different behavior is observed: In addition to reversible surface dynamics of Mn and O atoms, irreversible surface defect reactions due to oxygen, manganese vacancy or pair defect formation can evolve, influencing the stability of the surface. This defect chemistry seems to be correlated to the involvement of metal centers or lattice oxygen as redox active sites, critically depending on the nature of the electronic structure, i.e. the nature of the acceptor states for electrons. Correlating trends in ETEM with electrochemical studies by cyclovoltammetry, post mortem surface analysis and electronic structure calculations allow progress toward understanding atomic scale mechanisms of activity and stability of the electrodes. S. Raabe, D. Mierwaldt, J. Ciston, M. Uijttewaal, H. Stein, J. Hoffmann, Y. Zhu, P. Blöchl, and Ch. Jooss, Adv. Funct. Mater. 22 (2012) 3378. S. Mildner M. Beleggia, D. Mierwaldt Th. W. Hansen, J. B. Wagner, S. Yazdi, T. Kasama, J. Ciston, Y. Zhu, and Ch. Jooss, J. Phys. Chem. C, 119 (2015) 5301. D. Mierwaldt, S. Mildner, R. Arrigo, A. Knop-Gericke, E. Franke, A. Blumenstein, J. Hoffmann, C. Jooss, Catalysts 4 (2014) 129. J. Scholz, M. Risch, K.A. Stoerzinger, G. Wartner, Y. Shao-Horn, C. Jooss, J. Phys. Chem. C 120 (2016) 27746. M. Sotoudeh, S. Rajpurohit, P.E. Blöchl, D. Mierwaldt, J. Norpoth, V. Roddatis, S. Mildner, B. Ifland, C. Jooss, Phys. Rev. B 95 (2017) 235150. D. Mierwaldt, V. Roddatis, M. Risch, J. Scholz, J. Geppert, M. E. Abrishami, and C. Jooss, Adv. Sustainable Syst. 1 (2017) 1700109.

A.3.1
14:30
Authors : Nejc Hodnik
Affiliations : Department of Catalysis and Chemical Reaction Engineering, National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia

Resume : Nanoparticles catalytic performance is determined by the atomically precise architecture of structure, composition and morphology of their surface and near-surface area. In the catalysis community, this is commonly referred to as the structure-activity relationship. However, predicting, understanding and finally, designing wanted nanocrystal structure at the atomic-scale is far from straightforward. Much progress has been achieved concerning the synthesis procedure of the so-called as-synthesized nanoparticles. However, when particles get exposed to real conditions and a process of activation and degradation, forming the actual active centers of electrocatalysts, much is still to be learned, especially in the case of Pt-alloys. Advancements in the scanning transmission electron microscopy together with identical location approach have made it possible to track the electrochemical changes of the individual Pt-based nanocrystals. Such atomic-scale mechanisms are supported by Monte-Carlo simulations and very sensitive online dissolution measurements (ICP-MS). Our novel advanced multidisciplinary approach paves the way to the atomic-scale understanding of the dynamic structural and morphological evolution of nanostructures and thus deeper understanding of the structure-stability relationship. Pt is one of the most studied electrocatalysts. However, degradation mechanisms have not been explored sufficiently. For instance, Pt nanoparticles are known to dissolve and also to detach from the catalyst support due to carbon corrosion and for agglomerates. Insight into these mechanisms can provide us twofold information: (1) how to stabilize Pt nanoparticles (new ceramic-based supports) and (2) completely new Pt hydrometallurgical recycling protocols.

A.3.2
15:00
Authors : Jong-Eun Hong1,*, Seung-Gi Kim1, Dong Woo Joh1, Hafiz Ahmad Ishfaq1,2, Chanhoon Jung3, Jeong Hwa Park3, Hye-Sung Kim1, Tak-Hyoung Lim1,2, Seung-Bok Lee1,2, Seok-Joo Park1, Rak-Hyun Song1,2, Kang Taek Lee3,*
Affiliations : 1Fuel Cell Laboratory, Korea Institute of Energy Research (KIER), Daejeon, Korea 2Department of Advanced Energy and Technology, Korea University of Science and Technology (UST), Yuseong-gu, Daejeon, 34113, Korea 3Department of Energy Science and Engineering, DGIST, Daegu 42988, Korea

Resume : Microstructure tailoring has been attempted to improve the electrochemical reactivity of solid oxide fuel cell cathodes operated at intermediate temperatures. Cathode surface modification using electro-chemically reactive nano-catalysts has induced the increment of triple phase boundaries and electrode reactivity to oxygen reduction reaction. It has been also reported that Sr segregation may be inhibited by a microstructural modification on a conventional Sr- and Fe-doped LaCoO3 (LSCF) cathode, which results in durability enhancement. In this study, an in situ sol?gel process was applied to modify the cathode surface with an oxide ion conductor of Sm- and Nd-doped ceria (SNDC), in which the precursors of SNDC were ultrasonically infiltrated into the cathode and subsequently heated up while increasing temperature for measurement. The influence of surface microstructure tailored using SNDC particles is presented on the electro-catalytic property and electrochemical performance of conventional LSCF composite cathode. Sr segregation is also investigated when the oxide ion conducting particles are decorated at the LSCF cathode.

A.3.3
15:15
Authors : Denis Gryaznov (a), Maximilian F. Hoedl (b), Rotraut Merkle (b), Eugene A. Kotomin (a,b), Joachim Maier (b)
Affiliations : (a) Institute of Solid State Physics, University of Latvia, 8 Kengaraga, LV-1063, Riga, Latvia (b) Max Planck Institute for Solid State Research, Heisenbergstr. 1, D-70569, Stuttgart, Germany

Resume : Protonic ceramic fuel cells (PCFC) attract growing interest. Proton-conducting ceramics offer a higher ionic conductivity compared to oxide ion conductors, in particular at intermediate temperature (300-600°C). Finding optimum cathode materials with mixed protonic and electronic conductivity is crucial for PCFC performance. Proton concentrations were measured for several cathode materials [1], but an atomistic understanding of the parameters determining proton uptake is of great importance. We employed density functional calculations on the basis of the Hubbard (DFT U) approach and hybrid PBE0 exchange-correlation functional as implemented in VASP and CRYSTAL. The latter calculations for La(1-x)SrxFeO3-delta [2] yield protonic defects (hydroxide ions on regular oxygen sites) with similar geometry as in BaZr(1-x)YxO3-x/2 electrolytes, but much less negative hydration enthalpy. In the present study, we extend the calculations to nonstoichiometric Ba(1-x)SrxFeO3-delta and compare to La(1-x)SrxFeO3-delta. We present a detailed analysis of the density of states, volume and local geometry changes, oxidation and hydration energies as functions of oxygen deficiency (nominal Fe oxidation state). Thus, we strive for a comprehensive understanding of water incorporation in mixed protonic-electronic conductors. [1] R. Zohourian, R. Merkle, G. Raimondi, J. Maier, Adv. Func. Mater. 28 (2018), 1801241. [2] D. Gryaznov, R. Merkle, E. A. Kotomin, J. Maier, J. Mater. Chem. A 4 (2016), 13093.

A.3.4
15:30 Coffee break    
 
Defect chemistry II: Oxygen ion conductors : Session chair Federico Baiutti
16:00
Authors : Vincenzo Esposito
Affiliations : Technical University of Denmark, Department of Energy Conversion and Storage, Frederiksborgvej 399, 4000 Roskilde, Denmark

Resume : Oxygen defective metal oxides are electric charge-carriers ceramics that are rapidly defining a new generation of ionic-electronic systems, for energy, electro-mechanics, sensing and advanced electronics. In energy technologies, they are especially emerging for their wide range of functions and tunability that can be achieved by chemical strategies and nano-scaling. Nano-sizing has especially received great attention due to the possibility of getting properties that are very different from the bulk. In this presentation, I will show how oxygen defects can be the real player not only in controlling the electrical properties but also in tuning microstructure, mass diffusion and in generating new unexpected states of metastability at the nanoscale.

A.4.1
16:30
Authors : Iñigo Garbayo (a), Francesco Chiabrera (a), Nerea Alayo (a), José Santiso (b), Alex Morata (a), Albert Tarancón (a,c)
Affiliations : (a) Department of Advanced Materials for Energy Applications, Catalonia Institute for Energy Research (IREC), Jardins de les Dones de Negre 1, 08930 Sant Adrià del Besòs, Barcelona, Spain; (b) Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, Barcelona, 08193, Spain; (c) ICREA, Passeig Lluís Companys 23, 08010, Barcelona, Spain;

Resume : There is a growing interest in the development of fast oxide ion conductors for their application in energy and information technologies. Among the explored materials, Bi4V1.8Cu0.2O10.7 (BICUVOX) and, in general, stabilized bismuth vanadates are known to display one of highest ionic conductivity ever reported at intermediate temperature. Unfortunately, their poor chemical stability at T>500 ºC has traditionally hampered their use in bulk electrochemical devices. In this study, we unveil the possibility of employing BICUVOX in thin film form for low temperature applications, where it keeps its superior performance and, at the same time, shows a good stability over a wide range of oxygen partial pressure. BICUVOX thin films were deposited by pulsed laser deposition (PLD) method. First, a study on the effect of the deposition conditions on the structural and chemical properties of these films was conducted, evidencing the tremendous capability of PLD in tuning the film?s stoichiometry. Then, the ionic conductivity of the material was investigated by impedance spectroscopy. Since oxygen diffusion in BICUVOX is characterized by a strong anisotropy, we studied the conduction properties along the different atomic directions by preparing epitaxial films on SrTiO3 (001) and Nb-doped SrTiO3 (001) and measuring their conductivity in orthogonal directions (in-plane and out-of-plane configurations). The results showed that epitaxial thin films measured along the {VO3.5?0.5}2- layers possess the highest oxide ion conductivity ever reported at this temperature range (T < 300 ºC) and good electrochemical stability, demonstrating their potential use in solid state electrochemical devices at temperatures below 200ºC.

A.4.2
16:45
Authors : Alexander Shluger, Jack Strand, David Z. Gao
Affiliations : Department of Physics and Astronomy, University College London, London, UK; Department of Physics and Astronomy, University College London, London, UK and Università di Modena e Raggio Emilia, Via Amendola 2, 42122 Reggio Emilia, Italy; Nanolayers Research Computing Ltd., London, UK and Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway

Resume : Dielectric oxide films in electronic devices undergo significant structural changes during device operation under bias. These changes are usually attributed to aggregation of oxygen vacancies resulting in formation of oxygen depleted regions and conductive filaments. However, neutral oxygen vacancies have high diffusion barriers in ionic oxides and their interaction and driving forces for aggregation are still poorly understood. We will present the results of Density Functional Theory (DFT) calculations on the structure and properties of neutral dimers and trimers of oxygen vacancies in technologically relevant amorphous SiO2 and HfO2. These results demonstrate weak interaction between neutral O vacancies, which does not explain their quick aggregation. We propose that trapping of electrons, injected from an electrode, by the vacancies may result in creation of new neutral vacancies in the vicinity of pre-existing vacancies. The electron localization weakens Me?O bonds, which can be broken upon thermal activation, creating an O2- interstitial ion and a neutral O vacancy [1]. We describe this mechanism in a-SiO2 and demonstrate that this process becomes more efficient as the vacancy clusters grow larger [2]. These results demonstrate how the interaction between ionic and electronic species leads to structural and electrical changes in amorphous dielectric films. [1] D. Z. Gao, A.-M. El-Sayed, A. L. Shluger, Nanotechnology, 27, 505207 (2016). [2] D. Z. Gao, J. Strand, M. S. Munde and A. L. Shluger, Front. Phys. 7:43 (2019)

A.4.3
17:00
Authors : DJ Mannion, L Zhao, WH Ng, A Mehonic, AJ Kenyon
Affiliations : University College London; University College London; University College London; University College London; University College London

Resume : In some instances, barium strontium titanate (BST) [1,2] and titanium dioxide [4] capacitors have exhibited transients in their conductance as a response to step potentials. These transients involve an initial increase in conductance followed by a slower decrease in conductance, resulting in a distinctive peak in device current. They have previously been used to estimate the drift mobilities of oxygen vacancies and in our other work we have shown similar transients in amorphous silicon-oxide have uses in computation. It is proposed transients are the result of charged oxygen vacancies drifting under the applied bias. [3,4] However, having observed similar behaviour in our amorphous silicon-oxide devices, we question one of the key assumptions in this previous work and propose an alternative approach to investigating such transients. The analysis of these transients has historically involved comparing the voltage being applied and the time at which the current peak occurs - specifically the proportionality of the two. [1,2,5,6] Peaks in current are said to indicate the point in time at which vacancies have traversed across the device and begun collecting at the opposite electrode. This timing is therefore dependent on the drift properties of the vacancies and has been used to determine their mobilities. In addition to this, the same proportionality of peak timing and applied voltage has also been used to argue between causes of the behaviour. However, underlying this analysis is an assumption that transients are the result of a single cause. That both the rise and fall in conduction are the result of a redistribution of oxygen vacancies. Vacancies which act as donors, forming an n-type region at the negative electrode thus modulating the electronic conduction. [3] In this way, the two processes may be described with a single state variable ? the distribution of vacancies at a given point in time. If this held true, we would expect the two changes in conductance to have similar characteristics, particularly with respect to relaxation times. As vacancies relax to their thermal equilibrium position both the rise and fall in conduction should reset on similar timescales owing to them both being functions of vacancy distribution. However, our analysis finds these relaxation times differ significantly. It seems that to describe this system we require not just one state variable but two - one describing the increase in conductance and the second the decrease. We take an alternative approach and treat the rise and fall in conductance as two separate processes occurring in parallel. Although both cause a change in conductance, how long these changes persist varies between the two. For example, the increase in conductance is volatile on the order of seconds, its changes in conduction are lost between subsequent tests when left with no applied potential for more than a second. In contrast, the latter reduction in conductance is more permanent. These changes persist for minutes and the original state is only recovered after waiting for over half an hour at room temperature. Therefore, we find the relaxation times of the two processes differ significantly. If the assumption of a single cause is incorrect and only one of the changes in conductance is the result of vacancy drift, then the timing of the peak in current is no longer solely defined by the drift properties of the vacancies. It must also depend on a second unaccounted for effect. This puts any analysis assuming a common cause at risk of being inaccurate. By acknowledging that two effects may be occurring in parallel we have approached the problem from a different perspective. Rather than attempting to determine motilities from the timing of the current peak, we suggest to first characterise the processes independently in order to identify their respective mechanisms. We find the combination of two decaying exponentials fit the transients well allowing us to separate the two processes. With this approach, we have characterised the voltage dependency, activation energies and relaxation times of these processes. We believe this approach has potential to uncover further information regarding the mechanisms behind these current transients. [1] S. Zafar, R. E. Jones, B. Jiang, B. White, P. Chu, D. Taylor, and S. Gillespie, ?Oxygen vacancy mobility determined from current measurements in thin Ba0.5Sr0.5TiO3 films,? Appl. Phys. Lett., vol. 73, no. 2, p. 175, Jul. 1998. [2] S. Saha and S. B. Krupanidhi, ?Transient analysis in Al-doped barium strontium titanate thin films grown by pulsed laser deposition,? J. Appl. Phys., vol. 90, no. 3, pp. 1250?1254, Aug. 2001. [3] R. Meyer, R. Liedtke, and R. Waser, ?Oxygen vacancy migration and time-dependent leakage current behavior of Ba0.3Sr0.7TiO3 thin films,? Appl. Phys. Lett., vol. 86, no. 11, p. 112904, Mar. 2005. [4] N. Zhong, H. Shima, and H. Akinaga, ?Transient Current Study on Pt/TiO 2- x /Pt Capacitor,? Jpn. J. Appl. Phys., vol. 49, no. 4, p. 04DJ15, Apr. 2010. [5] J. Wang and S. Trolier-McKinstry, ?Oxygen vacancy motion in Er-doped barium strontium titanate thin films,? Appl. Phys. Lett., vol. 89, no. 17, p. 172906, Oct. 2006. [6] S. Zafar, H. Jagannathan, L. F. Edge, and D. Gupta, ?Measurement of oxygen diffusion in nanometer scale HfO2 gate dielectric films,? Appl. Phys. Lett., vol. 98, no. 15, p. 152903, Apr. 2011.2011.

A.4.4
 
Poster Session : Session chairs E. Gilardi, M. Spreitzer, F. Baiutti, F. Gunkel
17:30
Authors : Chuan-Hui Zhang, Bao Chen, Peng Shi, Liwu Jiang
Affiliations : National Centre for Materials Service Safety, University of Science and Technology Beijing

Resume : First-principles calculations have been performed on the perfect surface, point-defect surface, step-defect surface, layer-defect surface of Al2O3 film with water molecules (H2O) and chloride (Cl-) ions. The coadsorption mechanism has effect on the reaction and erosion of the surface. The adsorption energies (Eads), stable adsorbed sites, binding of film, charge transfer, reactants and products, activation energies and transition states are calculated and discussed. The results evidence that for the perfect Al2O3 surface, the critical monolayer of Cl- is 3/7, the Eads decrease in three steps, each Eads step only relate to the adsorbed site and the morphology. For point-defect surface, substitution point defects are more sensitive than vacancy point defects for reaction and erosion. The species of products depend on the energy barrier and orientation of water. For step-defect surface, Al1 step-defect and Al3 step-defect surfaces prefer to obtain Al-H2O compounds, while O2 step-defect surface prefers to form Al-Cl products. There is no obvious linear relationship between the number of products and the number of steps. For layer-defect surface, when low concentrations of Cl ions reach the surface, they prefer to erode the Al layer-defect surface with producing Al-Cl compounds, while they prefer to interact with H2O upon the O layer-defect surface.

A.P.1
17:30
Authors : M. Tyunina 1,2,* , D. Chvostova 2, A. Dejneka 2
Affiliations : 1 Microelectronics Research Unit, University of Oulu, Finland; 2 Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic

Resume : Allying epitaxial strain and synthesis conditions allows for the introduction of specific point defects in perovskite oxide films. In ferroelectric films, such defects lead to essential polar and electronic properties, which can enable advanced applications. Here, to elucidate the nature of the defects, optical constants are investigated in the spectral range of (0.7-8.8) eV in epitaxial ferroelectric barium titanate films, which are synthesized by pulsed laser deposition using different pressures of ambient oxygen. It is demonstrated that oxygen-vacancy-related defects are responsible for a peculiar transition below the bandgap at (2.7-2.9 eV) and significant blueshifts of (0.3-0.4) eV of the gap and the main interband transitions. These observations are discussed in terms of the defect-induced in-gap states and internal electic field. It is suggested that the defects are dipolar complexes comprising oxygen vacancies and trivalent titanium cations.

A.P.2
17:30
Authors : N.Korsunska1, L. Borkovska1, L. Khomenkova1, O. Gudymenko1, V. Kladko1, O. Kolomys1, V. Strelchuk1, C. Guillaume2, X. Portier2, O. Melnichuk3, L. Melnichuk3
Affiliations : 1V. Lashkaryov Institute of Semiconductor Physics of the NAS of Ukraine, 45 Prospect Nauky, 03028 Kyiv, Ukraine 2CIMAP, Normandie Univ, ENSICAEN, UNICAEN, CEA, CNRS, 6 Blvd. Maréchal Juin, 14050 Caen, France 3Mykola Gogol State University of Nizhyn, 2 Hrafska Str., Nizhyn 16600, Ukraine

Resume : Optical, electrical and structural properties of Tb and Eu co-doped ZnO films deposited by magnetron sputtering on Si and Al2O3 substrates were investigated by X-ray diffraction, photoluminescence (PL), micro-Raman and IR reflection methods. It is shown that incorporation of rare earth (RE) ions in ZnO host occurs under deposition and is accompanied by the formation of intrinsic defects in oxygen sublattice of ZnO. Both as-deposited and 600°C annealed films demonstrate Tb-related emission and no sign of energy transfer from ZnO host to RE ions and from Tb3 to Eu3 ions. A model of Tb3 emitting centers composed of Tb3 substituting zinc (Tb3 Zn) and interstitial oxygen (Oi) is proposed. Higher intensity of Tb-related emission in the film grown on Al2O3 substrate is found compared with that on Si correlated with larger amount of intrinsic defects and lower concentration of free electrons. It is ascribed to higher content of the emission centers. The annealing at 900°C is found to produce the out-diffusion of RE ions from ZnO grains, annihilation of the intrinsic defects and the increase of free carrier concentration. It leads to the formation of crystalline Tb2O3 phase in both types of the films and crystalline Zn2SiO4 phase in the film on Si substrate. In the PL spectra, the decrease of Tb3 -related PL and the appearance of two sets of Eu3 -related PL bands are found. This is ascribed to the segregation of Tb3 and Eu3 ions in the additional Tb2O3 and Zn2SiO4 phases. An effective energy transfer from Tb3 to Eu3 ions in these phases is assigned to the decrease of distance between these ions.

A.P.3
17:30
Authors : Jeho Na, Sung Haeng Cho, Jae-Eun Pi, Jaehyun Moon, Hee-Ok Kim, Seong-Deok Ahn, and Seung-Youl Kang
Affiliations : Electronics and Telecommunications Research Institute (ETRI) Daejeon, 34129, Korea

Resume : The fingerprint identification technology is widely used in mobile devices for biometric authentication because it is more convenient, faster, and safer than entering personal identification number (PIN) or password. As the demand for a mobile device with a full-screen display and one-handed operation while keeping the device flat on the table increases, the methods to put the fingerprint sensor on the front display are attracting great attention. For the on-display fingerprint sensor to be applied, the sensor should be transparent, without decreasing display resolution. Therefore, it is very important to choose proper transparent materials for both electrodes and active channel layers that do not be damaged while etching one from the other during the fabrication process. In this study, a transparent optical fingerprint sensor based on oxide semiconductor thin-film transistors (TFTs) with indium-tin-oxide (ITO) electrodes will be discussed. The triple layer active channel, deposited by sputtering with varying oxygen partial pressures, comprises an aluminum-doped indium-zinc-tin oxide (Al-InZnSnO), an indium-zinc oxide (IZO), and another Al-InZnSnO. The sandwiched IZO layer, having a lower bandgap than Al-InZnSnO, is employed as a light absorbing layer. The commonly known problematic phenomenon of persistent photoconductivity, mainly caused by the light-driven ionization of oxygen vacancy sites, in oxide semiconductors even after the removal of illumination has been successfully resolved by applying a short (< 1 ?s), positive gate bias pulse to the TFTs for electron accumulation. Acknowledgment This work was supported by the ?Development of Core Technologies for Transparent Flexible Display Integrated Biometric Recognition Device (2018-0-00202)? project from the Institute for Information & communications Technology Promotion (IITP) administered by Korea Ministry of Science and ICT (MSIT).

A.P.4
17:30
Authors : Chong Hwon Lee a,b, Yujin Lee a, Taewook Nam a, Sanghun Lee a, Il-Kwon Oh a, Joon Young Yang b, Dong Wook Choi b, Choongkeun Yoo b, Ho-jin Kim b, Woo-Hee Kim c,*, and Hyungjun Kim a,*
Affiliations : a School of Electrical and Electronics Engineering, Yonsei University, 50 Yonsei Ro, Seodaemun-gu, Seoul 03722, Korea b LG Display Co., Ltd., 245 LG-ro, Wollong-myeon, Paju-si, Gyeonggi-do 10845, Korea c Department of Materials Science and Chemical Engineering, Hanyang University, 55 Hanyangdeahak-ro, Sangnok-gu, Ansan, Gyeonggi-do 15588, Korea

Resume : We report the hydrogen barrier performance of sputtered La2O3 thin films for the device stability of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs). Hydrogen acts as a shallow donor in a-IGZO films, which makes TFTs conductive, resulting in degradation of their on/off properties. Since hydrogen can be easily incorporated by external environments or post processing, an appropriate hydrogen barrier is essential for enhancing device stability. La2O3, with its extreme electronegativity, can provide excellent hygroscopic characteristics. Because hydrogen exists in the form of -OH groups inside a-IGZO films, La2O3 is expected to be a promising barrier material for preventing hydrogen incorporation. Therefore, we investigate the growth characteristics of sputtered La2O3 thin films as hydrogen barrier layers, focusing on variations in growth rate, refractive index, and film stress, which depend on various process parameters, such as radio-frequency (RF) power, O2 partial pressure, and substrate temperature during reactive magnetron sputtering. The effects of these parameters on hydrogen barrier properties are systematically investigated and correlated with the microstructures of La2O3 films. The results demonstrate that La2O3 films grown with low RF power and low O2 partial pressure have an amorphous phase and provide excellent hydrogen barrier performance. We anticipate that these experimental results will help improve the environmental stability of a-IGZO TFTs.

A.P.5
17:30
Authors : D. Gryaznov, G. Zvejnieks, L.L. Rusevich, E.A. Kotomin
Affiliations : Institute of Solid State Physics, University of Latvia

Resume : Nowadays development of devices for energy storage applications, for the harvesting and mutual transformations of mechanical and electrical energies is of great interest [1]. In this respect (via utilizing the piezoelectric effect) ferroelectric perovskites are important materials for many technological applications. For a long time lead-zirconate-titanate (PZT) is the most widely used piezoelectric material for electromechanical applications. Recently several lead-free piezoelectrics were investigated. BaTiO3-based (BTO) piezoelectric materials e.g. BTO solid solutions with SrTiO3 (STO) are considered as potential substitution for PZT [2]. In this study, we explore the piezoelectric properties of tetragonal STO/BTO superlattice by varying the number of STO and BTO layers. Our theoretical calculations are based on the first principles approach and hybrid (B1WC) exchange-correlation functional as implemented into CRYSTAL computer code. The direct piezoelectric tensor constant (e33) calculations are based on the Berry phase approach using numerical derivatives. On the basis of group theory analysis, we demonstrate that tetragonal heterostructure theoretically could be described using one of two different space groups, that are distinguished by forbidden or allowed TiO6 octahedra rotation around the z-axis. Using different number of relative Ba/Sr layers in STO/BTO heterostructure, we demonstrate that both space groups lead to similar results for small and average STO relative concentrations, when, e33, increases with the concentration of STO, with respect to pure BTO. The different scenarios are suggested for high STO concentrations, when TiO6 octahedra rotation affects the results. [1] C.R. Bowen, et al, Energy Environ. Sci. 2014, 7, 25. [2] L. Rusevich, G. Zvejnieks, et al., J. Phys. Chem. A 2017, 121, 9409.

A.P.6
17:30
Authors : Markus Kubicek, Matthäus Siebenhofer, Ghislain M. Rupp, Jürgen Fleig
Affiliations : TU Wien, Institute of Chemical Technologies and Analytics, Getreidemarkt 9, 1060 Wien, Austria

Resume : Thin films of mixed conducting ionic materials may be used as electrodes for batteries or solid oxide fuel cells, layers used for resistive switching, etc. For deposition of such layers special thin film preparation techniques are necessary. Pulsed laser deposition (PLD) is of particular importance as it allows to deposit even very difficult multi-element compositions almost unchanged from a target material to produce thin films. Still the properties of the thin films may differ from bulk or other thin films due to different parameters such as temperature, gas pressure, laser energy or target to substrate distance. A novel in-situ combination of electrochemical impedance spectroscopy (EIS) and PLD is presented and shown to give direct insight into the electrochemical properties of growing films. Deposition related changes of single crystalline substrates are reported which could be uniquely measured with the described in-situ technique. Development of oxygen transport resistances and defect chemistry (measured via the chemical capacitance of a thin film) with thickness, different grain size or multilayers is investigated for mixed ionic and electronic conducting materials such as La1-xSrxCoO3-?.

A.P.7
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Harvestore Invited Session : Session chair Matjaz Spreitzer
09:00
Authors : A. Tarancón
Affiliations : ICREA

Resume : The internet of things (IoT) will revolutionise the way in which we interact with the world around us: sensors of temperature, presence, traffic density will measure data and communicate to a control unit for decision-making. Autonomous actions for process optimization, intervention, environmental safeguard will be taken without human intervention. Embracing the IoT in our lives will require the advent of a new generation of portable power sources. For this, new families of rechargeable and autonomous micro-energy sources offering high specific power (0.5-10 mW and 1-100 J) have to be developed in order to integrate the required power capabilities in the IoT nodes. These new technologies will be necessarily miniaturizable and likely based on advanced concepts of Nanoionics and Iontronics, i.e. will take advantage of ion-based local effects at the nanoscale. This way, surprising properties of fast conduction and high storage capacity can be obtained. Moreover, by taking advantage of silicon microfabrication techniques, a superior manufacturability, cost-effectiveness and the possibility to host dense structures in a seamless architecture will be reached; all in an environmentally friendly material. In this talk, we will present the HARVESTORE project devoted to integrate harvesting and storage units based on new concepts in silicon technology while reviewing interesting concepts of Nanoionics and Iontronics.

A.6.1
09:30
Authors : Markus Kubicek, Alexander Viernstein, Maximilian Morgenbesser, Jürgen Fleig
Affiliations : TU Wien, Institute of Chemical Technologies and Analytics, Getreidemarkt 9, 1060 Wien, Austria

Resume : Mixed ionic and electronic conducting (MIEC) perovskite oxides are important for several energy applications. Among those, (Fe-doped) strontium titanate (Fe:STO) is one of the best investigated materials. The band gap of STO of ~3.2 eV at room temperature enables several effects upon UV irradiation, revealing a much more complicated interplay of charge carriers than for purely electronic photoactive materials. STO and Fe:STO single crystals were investigated to study photochromism, photoconductivity, changes in oxygen surface kinetics, and photo-related oxidation or reduction reactions. A bulk-related color-change of Fe:STO single crystals at elevated temperatures from pristine yellowish/transparent to black upon illumination was observed. Due to enhanced oxygen incorporation upon illumination, the bulk stoichiometry of the whole single crystal is changed, which results in the color change. The investigated electrochemical properties showed a defect chemical state equivalent to an internal p(O2) >10^9 Pa. Additionally the influence of different electrodes in photoelectrochemical devices based on STO are investigated. These defect chemical changes can also be exploited in high temperature photovoltaics, in solid photoelectrochemical cells (SOPEC) or in a ?photo-charged? battery. Here, STO was used together with thin films of yttria stabilized zirconia and different top- and bottom-electrodes to generate photocurrents and photovoltages of up to 1 V at 350-400°C.

A.6.2
10:00
Authors : Guus Rijnders
Affiliations : MESA+ Institute for Nanotechnology, University of Twente, POBox 217, 7500AE, Enschede, the Netherlands

Resume : In recent years, it has been shown that novel functionalities can be achieved in oxide heterostructures in which the interfaces are atomically controlled, in terms of atomic stacking as well as in terms of the local symmetry. In this contribution, I will highlight the recent developments in atomic controlled growth of epitaxial oxides by pulsed laser deposition, with a focus on the effect of the oxidation state of de deposited species on the growth. Furthermore, I will discuss integration of epitaxial complex oxides in Si and III-V technology, which has recently attracted a lot of attention in science and industry. Such complex oxides include, amongst others, ferro- and piezo-electrics and materials for resistive switching devices. In this presentation I will focus on the integration of Pb(Zr,Ti)O3 (PZT) with Si and III-V semiconductors. The epitaxial integration of PZT with Si and for instance GaN is hampered by the difference in crystal structure and large lattice mismatch. Using epitaxial buffer layers and optimized growth with pulsed laser deposition, we are able to obtain epitaxial growth of PZT on, for instance, MgO-buffered GaN. The thickness of the MgO can be lowered down to single monolayers while maintaining the high quality and good properties of epitaxial PZT films, which enable practical applications for high power FET?s and non-volatile ferroelectric controlled electronics devices.

A.6.3
10:30 Coffee break    
 
Micro-/Nanodevices : Session chair Alex Morata
11:00
Authors : Stefan Tappertzhofen 1,2, Sebastian Bette 2, Giuliana Di Martino 3, Stephan Hofmann 1
Affiliations : 1 Department of Engineering, University of Cambridge, Cambridge, United Kingdom; 2 now with aixACCT Systems GmbH, Aachen, Germany; 3 Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom

Resume : Memristive devices are the building blocks for new memory concepts such as storage class memories, and can even emulate neuromorphic and logic functions. Their non-linear and ultra-fast as well as energy-efficient working principle is based on ionic redox reactions on the nanoscale that allow for atomically scaled manipulation of conductive nanoparticles and filaments in an insulating switching matrix. The electrochemical interactions and the dynamics of these reactions are still open questions, making significant device optimization challenging. We report on the formation and dissolution of metal clusters in silicon dioxide acting as a model host material system analyzed by transmission electron microscopy. Our study is complemented by applying a novel spectroscopic technique that allows for in-operando characterization of memristive switching by monitoring plasmonic resonances of the embedded nanoparticles and filaments. The optical signatures we detect indicate partial filament dissolution during device operation which is supported by electron microscopy studies and statistical analysis of the switching properties. Our results indicate a complex and dynamic interplay between electrochemical properties such as nucleation, redox rate, and defect concentration and velocity. We discuss the implication of these findings on the device performance and stability.

A.7.1
11:30
Authors : Carola Ebenhoch*, Julian Kalb*, Joohyun Lim**, Christina Scheu**, Lukas Schmidt-Mende*
Affiliations : *Department of Physics, University of Konstanz, 78457 Konstanz, Germany; **Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany

Resume : Understanding and controlling the ionic effects inside TiO2 nanowires are of great interest since they strongly influence the optoelectronic properties. Especially, when thinking about their implementation in devices, such as emerging solar cell technologies, transistors, and resistive random access memory devices, it is crucial to know how their behavior is influenced by the crystal structure and its defects, such as vacancies or interstitials and others. A systematic study of hydrothermally grown TiO2 nanowires at different temperatures allows us to get an insight into the impact of the internal defect structure on the memristive switching mechanism, and its retention time. The growth of these nanowires on a conductive substrate leads to an array of perpendicular grown nanorods, which show a finger like structure at the very top. Dependent on the growth temperature, the finger diameter can be varied. This allows us to investigate the impact of changes in grain boundaries. The oxygen vacancy density can be directly correlated to the change in the memristive behavior. Furthermore, to investigate the influence of the electrode we have compared two types of architectures, namely FTO/TiO2/Au and FTO/TiO2/FTO.

A.7.2
11:45
Authors : M. Bianchini, N. Alayo, I. Garbayo, F. Chiabrera, (1) M. Salleras, L. Fonseca, (2) A. Tarancón (1,3)
Affiliations : 1 Catalonia Institute for Energy Research (IREC), Department of Advanced Materials for Energy, 08930, Sant Adriá del Besòs, Barcelona, Spain 2 IMB-CNM (CSIC), Institute of Microelectronics of Barcelona, National Center of Microelectronics, CSIC, Campus UAB, 08193, Bellaterra, Barcelona, Spain 3 ICREA, 08010, Barcelona, Spain

Resume : Exhaust gas monitoring in combustion operations is a crucial element for the process control-loop which allows for maximizing the energy output and reducing the emission of pollutants in many sectors ? e.g. coal-fired power plants, automotive and gas boilers. Among the existing sensing devices, solid-state micro-sensors are of great potential interest due to their low cost, small size, fast start-up, low detection limit and quick response ? features enabled by means of thin-film technology and mainstream microfabrication processes. Currently, the leaking of oxygen from the reference chamber is considered the main issue to operate solid-state micro-sensors at the high temperatures required. Besides, many studies on thin-films fabricated by PLD or sputtering show the presence of pinholes, which inevitably leads to electrical short-circuit across the electrolyte. In this study, we report a novel design and fabrication route for a solid-state potentiometric oxygen sensor fully integrated in silicon technology based on a self-sustained YSZ membrane and ceramic electrodes. Two approaches for its hermetic encapsulation are discussed: glass frit sealing and anodic bonding. Moreover, we present the characterization of a 20 nm-thick embedded layer of pure tetragonal ZrO2 fabricated by ALD that allows for the improvement of the electrolyte reliability by preventing the formation of pinholes. This system addresses the main limitations of the commercial oxygen sensors and of benchmark solid-state micro-sensors. At the same time, it allows for a great flexibility in the design (e.g. the possibility of introducing heating paths), thus tackling some important issues related to the mechanical, chemical and thermal stability of the system.

A.7.3
12:00
Authors : J. L. Frieiro,1,2 J. López-Vidrier,1-3 O. Blázquez,1,2 D. Yazicioglu,3 S. Gutsch,3 J. Valenta,4 M. Zacharias,3 S. Hernández,1,2 B. Garrido1,2
Affiliations : 1 MIND, Department of Engineering: Electronics, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona, Spain 2 Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Av. Joan XXIII S/N, E-08028 Barcelona, Spain 3 Laboratory for Nanotechnology, Department of Microsystems Engineering (IMTEK), University of Freiburg, Albert-Ludwigs-University Freiburg, Georges-Köhler-Allee 103, D?79110 Freiburg (Germany) 4 Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic)

Resume : Over the last two decades, Si nanocrystals (NCs) have been extensively studied because of their size-dependent electronic properties. More recently, Si suboxides have demonstrated the resistive switching (RS) phenomenon, broadening their field of application to resistive random-access memory (RRAM) devices. The combination of their emission properties with the RS phenomenon could open the possibility of developing a new family of RS devices based on Si technology with an optical readout, under electrical excitation. In this work, we have investigated the RS and the electroluminescence (EL) of Si NC/SiO2 multilayers (MLs) in a ZnO/Si NCs/Si device. Thin dielectric layers of SiO2 and Si3N4 were introduced either on top or at the bottom of the Si NCs/SiO2 MLs for controlling carrier injection. After the electroforming process, the devices exhibited stable RS properties, with differences in the set and reset voltages between the different structures studied, and an endurance of more than 1000 cycles when pulsing the writing and readout voltages in some cases. We observed that the emitted EL is clearly different in each resistance state, having either no emission, emission from the top electrode (defects) or from Si NCs, depending on the dielectric layers present, the polarization and the resistance state. Overall, such an occurrence states the demonstration of a Si NCs-based electroluminescent memristor, which paves the way for the future integration of Si-based memristors into photonic integrated circuits.

A.7.4
12:15
Authors : K.-H. Heinig*, H.-J. Engelmann*, A. Gharbi°, R. Tiron°, T. Prüfer*, J. von Borany*
Affiliations : * Helmholtz Zentrum Dresden-Rossendorf, Dresden, Germany ° CEA-LETI, Grenoble, France

Resume : The transistor pathway predicts an evolution from lateral MOSFETs via FinFETs to vertical nanowire gate-all-around FETs (vNW GAA-FET). Our European project IONS4SET [1] goes a step further: Aiming at low-power electronics, the principle of operation of transistors will be changed from field effects to single electron tunneling via a Si quantum dot (QD) in SiO2. Room temperature (RT) operation of Single Electron Transistors (SETs) requires Si QDs of ~3 nm and tunneling distances of < 1 nm. The SiO2 with the embedded Si QD has to be ~ 5nm thick. To fabricate vNW GAA-SETs, Si nanopillars with ~5nm SiO2 have to be fabricated by Electron Beam Lithography and Reactive Ion Etching (RIE). Here we report on a dramatic SiO2 thickness reduction in the Si/SiO2/Si layer stack by RIE of nanopillars. It is strongly pillar diameter dependent: In 100 nm pillars the thickness remains almost unchanged, but for < 20nm it shrinks from 8nm to ~3nm as shown by Energy-Filtered Transmission Electron Beam Microscopy (EFTEM). Modeling, computer simulation and dedicated experiments reveal that it is due to a huge number of electric breakdowns during RIE. A breakdown forms a SiOx filament which emits O in SiO2. Each O atom of the SiO2 becomes many times an O interstitial, which in most cases recombines with an O vacancy. Depending on diameter, some O will emanate from the edge of the SiO2 disk leading to the dramatic oxide thinning. [1] This work has received funding from the European Union?s Horizon 2020 research and innovation programme under grant agreement No 688072 (www.ions4set.eu).

A.7.5
12:30 Lunch break    
 
Lithium batteries : Session chair Elisa Gilardi
14:00
Authors : Mark Huijben
Affiliations : MESA+ Institute for Nanotechnology, University of Twente

Resume : Lithium-ion batteries are the most popular rechargeable batteries nowadays, as they have become the main power source for many applications. However, none of the current rechargeable batteries can fully satisfy all challenging requirements for current energy storage. Essential for all high performance energy applications are processes that happen at the interfaces between the different components. Key problems include slow electrode process kinetics with high polarization and low ionic diffusion or electronic conductivity, particularly at the electrode-electrolyte interfaces. Epitaxial engineering is used to control the crystal orientation of electrode thin films, which enables a unique insight into the relation between electrochemistry and crystal directionality of such chemically complex inorganic interfaces, not obtainable in single crystals or polycrystalline samples. Here, I will show the lithium diffusion behavior in LiMn2O4 cathode, and Li4Ti5O12 anode, thin films, which are epitaxially grown by pulsed laser deposition on single crystalline Nb-doped SrTiO3 substrates. Control over the specific crystal orientation of the full thin film enables detailed analysis of the lithium diffusion along specific crystal planes ({001}, {110} and {111}). Single phase films show enhanced cyclability and faster charging speed, as compared to studies on polycrystalline materials.

A.8.1
14:30
Authors : Eduard Querel, Federico Pesci, Rowena Brugge, Andrea Cavallaro and Ainara Aguadero
Affiliations : Department of Materials, Imperial College London, SW7 2AZ, London , UK

Resume : Solid state batteries are pose to be the next generation of safer batteries that aims to substitute the state-of-the-art liquid flammable electrolytes based batteries. The further integration of Li or Na metal anodes opens the door to higher energy densities and novel battery electrochemistries. The development of these systems has been however, so far hindered by the lack of understanding of the dynamic metal/solid interfaces that leads to chemical, electrochemical and mechanical degradation during cell operation. Two of the best solid state alkaline-ion conductors are derivatives of Li7La3Zr2O12 Garnet-type structures for Li and Na3Zr2Si2PO12 NaSICON type structures for Na able to reach values of 10-1 mS/cm at RT. In this work, we focus on the study of Na/NaSICON and Li/Garnet interfaces paying particular attention to the effect that different processing conditions can have on the microstructure, local chemical composition of bulk, surfaces and grain boundaries. All these parameters have a direct impact on the Li and Na-ion dynamics leading to significant implications on the cell performance in terms of power density and cycle life due to different degradation issues such as SEI and dendrite formation. Our main results highlight the complexity of these systems and propose new in situ techniques to gain a deeper understanding of the processes taking place. In this regard, we introduce a novel and beyond state-of-the-art dual secondary ion mass spectrometer (SIMS) aimed at innovative 3D chemical and microstructural analysis with in operando capabilities.

A.8.2
15:00
Authors : N. Kuganathan, D. C. Parfitt, and A. Chroneos
Affiliations : Faculty of Engineering, Environment and Computing, Coventry University, Priory Street, Coventry CV1 5FB, United Kingdom

Resume : Lithium metatitanate, Li2TiO3, is a potentially technologically important material for fusion reactors and lithium batteries. Atomistic simulations are used to investigate the defect processes of bulk in Li2TiO3 and a series of interface structures. In the bulk material it is calculated that the activation energy of migration of lithium ions via the vacancy mechanism is 0.51 eV (ab plane). Interface structures are employed to gain an understanding of how these can be utilised to increase oxygen diffusivity. Finally, trivalent dopants are introduced to increase the lithium vacancy concentration and their impact is validated both at the bulk and at interfaces.

A.8.3
15:15
Authors : A. Morata , V. Siller , F.Chiabrera, M. Stchakovsky, A. Tarancón
Affiliations : A. Morata ; V. Siller ; F.Chiabrera: IREC, Jardins de les Dones de Negre 1, Planta 2, 08930, Sant Adrià del Besòs, Spain M. Stchakovsky: HORIBA Scientific, Avenue de la Vauve, Passage Jobin Yvon, 91120 Palaiseau, France A. Tarancón: ICREA, Passeig Lluís Companys 23, 08010, Barcelona, Spain

Resume : Ionic transport in solids is governing the performance of devices in a wide range of fields like batteries, solid oxide cells, supercaps, memories etc. This is driving scientific efforts to continuously improve materials in order to fulfil increasing performance, durability and safety requirements. For this reason, it is imperative improving the understanding of ionic intercalation and diffusion phenomena. In operando techniques are especially useful because they allow accessing the relevant processes at the moment they are taking place. Here we introduce a new procedure based on spectroscopic ellipsometry (SE) for the in-operando measurement of ion diffusion phenomena. SE is a well-known powerful technique for thin film characterization that provides precise information on morphology, thickness, and optical properties. Here we use these capabilities for the study of ionic conductor materials. Different cases of study are presented, including Li+ cathode for batteries (LiMn2O4) and O2- ionic conductors relevant in high temperature electrochemical devices (La1-xSrxFeO3-). Two in-operando cells have been designed for different purposes: a liquid cell for electrochemical cycling and a high temperature atmospheric cell for PO2 studies up to 400°C. Fast transient experiments have also been carried out that demonstrate the excellent time resolution of the technique (in the milliseconds range). Remarkably, we show how the response of the optical properties of a LiMn2O4 film to a potential step can be used used to determine the Li+ diffusion coefficient of the material. The presented results demonstrate the high capability of SE as non-destructive in-operando characterization technique for the study of ion-transport phenomena.

A.8.4
15:30 Coffee break    
 
Thin films & interfaces I : Session chair Christoph Baeumer
16:00
Authors : Scott A. Chambers
Affiliations : Physical & Computational Sciences Division, Pacific Northwest National Laboratory, Richland, WA

Resume : We have developed a new algorithm for extracting potential profiles from core-level x-ray photoelectron spectra measured on buried interfaces. Significantly, deeply buried interfaces are accessible by using hard x-ray excitation. We have applied this method to understanding the detailed energy landscape associated with epitaxial n-SrTiO3/p-Ge(001) heterojunctions with film thicknesses ranging from 3 u.c. (1.2 nm) to 32 u.c (12.8 nm) . This system is a promising photocathode candidate for the hydrogen evolution reaction (HER) accompanying water splitting. We find that the Ge bands bend strongly downward as the interface is approached from the bulk, but that the SrTiO3 bands are relatively flat, in large part due to Fermi-level pinning within a few tenths of an eV of the conduction band minimum. The conduction band offset is near zero. Therefore, photo-generated electrons in the Ge have an energetically downhill drift across the interface to an electrolytic aqueous solution and have sufficient energy to drive the HER. The resulting incident light-to-photocurrent conversion efficiency is 14% for the highly reflective epitaxial film surface in a buffered pH 7 electrolyte solution. However, thinner films delaminate as a result of exposure to the electrolytic solution.

A.9.1
16:30
Authors : Agham Posadas, Alexander A. Demkov
Affiliations : Department of Physics, The University of Texas at Austin, Austin, Texas, United States

Resume : SrTiO3 is one of a handful of oxides that can be grown in single crystalline form directly on silicon. Originally envisioned as a gate dielectric for scaled CMOS technology because of its very high dielectric constant, one critical issue that prevented this technology to be developed is the near zero conduction band offset with Si making it unsuitable for use as a gate insulator because electrons can simply flow through SrTiO3 with ease. In the first part of the talk, I will describe how one can take advantage of this behavior so that SrTiO3 can be used as a protection layer for Si photocathodes in a water-splitting photoelectrocatalysis cell, allowing for efficient extraction of the photogenerated electrons for hydrogen generation, while preventing the corrosion of Si when submerged in water. In the second half of the talk, I will discuss the high redox activity of SrTiO3, particularly with respect to oxide thin film deposition, which has typically been glossed over by thin film growers. In many cases, there will be an unavoidable interfacial layer of highly oxygen-deficient SrTiO3 formed at the interface with the top oxide film.The ease by which oxygen ions flow out of SrTiO3 when a sink for oxygen is present has significant implications for the interpretation of interfacial 2DEGs with SrTiO3 and also opens up a new method for growing epitaxial suboxides including EuO, VO, and NbO2.

A.9.2
17:00
Authors : Hrishit Banerjee, Oleg Jansen, Karsten Held, Tanusri Saha-Dasgupta
Affiliations : Technische Universitat (TU) Graz, IFW Dresden, Technische Universitat (TU) Vienna, Indian Association for the Cultivation of Science (IACS) Kolkata.

Resume : The exotic case of the experimental observation of a ferromagnetic insulating ground state in interfaces formed by oxide hetero-structures of Lanthanum Manganate (LaMnO_3 ) and Strontium Titanate (SrTiO_3 ) has puzzled theorists and experimentalists alike for some time. There has been some suggestions to the origin of this behavior from the perspective of crystal symmetry breaking and orbital ordering emerging due to an intrinsic difference in the Jahn-Teller distortions within the LMO unit cell arising due to a slight monoclinicity in the unit cell which however seems unlikely to happen in the experimental case where LMO thin films are grown epitaxially over thick STO substrates which plausibly forces LMO to conform to the symmetry of the substrate which is tetragonal in nature, or even exotic magnetic ground states. However these still do not satisfactorily explain the phenomena. In this study we aim to show the effect of electronic exchange and correlation in driving a ferromagnetic insulating state in LMO/STO interfaces, due to electronic instabilites arising in the system, giving rise to charge disproportionation leading to an insulating state from first principles calculations, which is not captured correctly by purely Density Functional Theory based methods, and one requires the use of hybrid Hartree-Fock exchange functionals to correctly estimate the effect of these electronic instabilities. Our study also shows that unlike some previous suggestions the polar catastrophe electron gas in our calculations does not reside in the LMO layers, but on the STO slab as seen in general in cases of oxide hetero-structures. Thus our study tries to satisfactorily explain the charge transfer and the emergence of the ferromagnetic insulating state due to the inherent instabilities in the system, captured correctly by hybrid functionals.

A.9.3
17:15
Authors : M. Rose, B. ?míd, M. Vorokhta, H. Bluhm, F. Gunkel, D. N. Mueller and R. Dittmann
Affiliations : Institute for Electronic Materials (IWE 2), RWTH Aachen, Aachen, GER (M.Rose, F. Gunkel); Peter Gruenberg Institute, Forschungszentrum Juelich, Juelich, GER (M.Rose, F. Gunkel, R. Dittmann); Dep. of Surface and Plasma Science, MFF UK, Charles University, Prague, CZ (B. ?míd, M. Vorokhta); Chemical Sciences Division, Lawrence Berkeley National Lab., Berkeley, USA (H. Bluhm)

Resume : The electronic properties of oxide heterointerfaces depend on their ionic constitution and defect structure: Ionic charges contribute to the charge transfer and the charge screening at oxide interfaces, triggering a thermodynamic balance of ionic and electronic structure. In this study, we simultaneously access electronic and ionic structure of the prototypical charge-transfer-heterointerface, LaAlO3/SrTiO3 (LAO/STO), by in-situ photoemission spectroscopy under applied oxygen pressure (near ambient pressure XPS). Using NAPXPS, we deconvolute the chemical and electronic recombination of the buried interface in-situ and as a function of a varied oxygen atmosphere at elevated temperatures (470°C). In this way, we embrace both, the rich chemistry of complex oxides and the rich electronics of nanoscaled oxide heterointerfaces. As we demonstrate, the LAO/STO interface is characterized by the depletion of the 2DEG through incorporation of Sr vacancies when oxygen atmosphere is applied. Electrons and Sr vacancies show an inverse and reversible behavior as is indicated by an alternating appearance of a Ti3+ peak in the Ti2p emission spectra and a secondary doublet in the Sr3d emission spectra.. Using a synchrotron-based NAPXPS, a depth profiling of the Sr phases becomes possible, confirming the oxygen partial pressure dependent appearance of additional Sr at the LAO surface. As we show, on the nanoscale the electron transport in oxide heterointerfaces is affected by ionic motion already at temperatures while their dynamics appear frozen in the bulk. The mobility of ionic species is thus increased due to lowered dimensionality, internal band bending and strong electric fields rendering fundamentally different ionics phenomena.

A.9.4
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09:00 Plenary Session (Main Hall)    
12:30 Lunch break    
 
Memristors : Session chair Markus Kubicek
14:00
Authors : K. Maas (a); E. Villepreux (b); L. Rapenne(a); E. Salas?Colera (c,d); D. Cooper (b); C. Jimenez(a); G. R. Castro (c,d); Q. Rafhay (e); M. Boudard (a); and M. Burriel (a)
Affiliations : (a)Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France (b)CEA, LETI, Minatec Campus, F-38054 Grenoble, France (c)European Synchrotron, SpLine CRG BM25 Beamline, 71 Ave Martyrs, F-38000 Grenoble, France (d)CSIC, ICMM, Madrid 28049, Spain (e) Univ. Grenoble Alpes, CNRS, IMEP-LAHC, F-38000 Grenoble, France

Resume : The interest to increase the performance of data storage technologies is leading to the development of new types of memory architectures. In particular, memristive devices based on a valence change mechanism are now considered as potential candidates for both long-term memory storage and brain-like computing [1]. As La2NiO4+? has the particularity of being able to accommodate a large range of oxygen oversotichiometry while maintaining its crystal structure, we selected this MIEC oxide to build novel memristive devices. The presence of oxygen interstitial point defects in the structure is compensated by positive holes to keep charge-neutrality, and thus leads to a change in the electrical characteristics of the material. Highly-oriented and dense La2NiO4+? thin films were grown using pulsed-injection metal-organic chemical vapor deposition. The electrical response of these devices could be tuned both by changing the electrode materials and the amount of point defects (oxygen interstitials) of the sandwiched film. The chemical, structural, microstructural and electrical characterization of the films will be presented, showing the high crystal-quality, the change in Ni oxidation state and the concomitant change in resistivity after annealing. Furthermore, the key role played by the oxygen interstitials on the initial resistance state, the initialization step and the memristive characteristics of the devices will also be discussed.

A.10.1
14:45
Authors : Ashis Manna1, A. Barman2, Shalik R. Joshi1, B. Satpati3, P. Dash1, Ananya Chattaraj2, S. K. Srivastava4, P. K. Sahoo5, A. Kanjilal2, D. Kanjilal6, and Shikha Varma1
Affiliations : 1. Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005, India 2.Department of Physics, School of Natural Sciences, Shiv Nadar University, Gautam Buddha Nagar, Uttar Pradesh 201314, India 3.Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata,700064, India 4. Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India 5. School of Physical Sciences, National Institute of Science Education and Research, Jatni, Odisha India 6.Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110 067, India

Resume : We investigate here the structural phase transformation and electrical resistive switching properties of TiO2 thin films (80 nm) after their self-ion implantation with 50 keV Ti+ ions at several fluences. UV-Raman, grazing incidence x-ray diffraction (GIXRD), transmission electron microscopy, x-ray photoelectron spectroscopy, and atomic force microscopy techniques have been utilized to investigate the modifications in thin films. Both, the as-grown and ion implanted, films display mixed phases of rutile (R) and anatase (A). Surprisingly, however, a phase transition from A to R is observed at a critical fluence, where some anatase content transforms into rutile. This A to R transformation increases with additional fluence. The critical fluence found by GIXRD is slightly smaller (1 x 1013 ions/cm2) than from UV-Raman (1 x 1014 ions/cm2), indicating the first initiation of phase transformation probably in bulk. All the films contain anatase in nanocrystalline form also and the phase transformation seems to take place via aggregation of anatase nanoparticles. Thin films also show the presence of oxygen vacancies (OV ) Ti3+ , whose number grows with fluence. These OV as well as thermal spikes created during Ti+ ion implantation are also crucial for the A-R transition. After implantation at the highest fluence, TiO2 thin films show bipolar resistive switching behavior. The development of conducting filaments, formed by the migration of many oxygen vacancies generated during ion implantation, can be responsible for this behavior.

A.10.3
15:00
Authors : Raquel Rodriguez-Lamas(a)*, Dolors Pla(a), Odette Chaix-Pluchery(a), Hervé Roussel(a), Laetitia Rapenne(a), Xavier Mescot(b), Quentin Rafhay(b), Michel Boudard(a), Carmen Jiménez(a), Mónica Burriel(a)
Affiliations : (a) Univ. Grenoble Alpes, CNRS, Grenoble INP1, LMGP, F-38000 Grenoble, France (b) Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP1, IMEP-LAHC, F-38000 Grenoble, France 1 Institute of Engineering Univ. Grenoble Alpes

Resume : As the need of increasing data storage arises, new candidates for non-volatile memories are required. Valence change memories (VCM) are one of the promising ones given their recent performance demonstrations in terms of switching time, switching energy and retention[1]. Resistive switching (RS) in VCMs occurs due to the drift of oxygen vacancies together with the concomitant redox reaction at the nanoscale. A TiN/LaMnO3+? (LMO)/Pt heterostructrure was chosen to build our VCM nanoionic devices, as LMO is able to accommodate a flexible oxygen stoichiometry by varying the Mn3+/Mn4+ ratio. Polycrystalline thin films were prepared on platinized silicon [2] with TiN electrodes sputtered on top, obtaining devices in ?top-bottom? configuration. The TiN/LMO/Pt devices can be operated both in a counter clock wise (CCW) or in a clockwise (CW) regime, being the change in switching direction highly dependent on the induced current asymmetry. While the CCW regime shows highly reproducible RS with HRS/LRS ratios between 2 and 10 and endurances of up to 100 cycles, the CW regime presents endurances of only a few cycles, and HRS/LRS ratios which are comparable or smaller to those of the more stable and reproducible CCW regime. [1] R. Waser, J. Nanosci. Nanotechnol. 2012, 12, 7628. [2] R. Rodriguez-Lamas, D. Pla, O. Chaix-Pluchery, B. Meunier, F. Wilhelm, A. Rogalev, L. Rapenne, X. Mescot, Q. Rafhay, H. Roussel, M. Boudard, C. Jiménez, M. Burriel, Beilstein J. Nanotechnol. 2019, 10, 389.

A.10.4
15:15
Authors : Asif Ali , Jung Jongwan
Affiliations : Department of Nanotechnology and advanced materials engineering, Sejong University, Seoul, Korea

Resume : INTRODUCTION Because of device scalability and low power consumption, the resistance-based memories are favorable candidates to replace charge-based memories. Therefore, resistive random access memories (RRAM) are an excellent candidate for next generation memories [1]. Depending on operation mechanism, types of RRAM can be classified into two classes: Conductive Bridge RAM (CBRAM) and Valence Change RAM (VCRAM) [2]. CBRAM is favored over VCRAM due to its large ON/OFF ratio. The metallic film in CBRAM is considered to be denser than oxygen vacancy based filament. In CBRAM, type of switching polarity behaviors is strongly affected by dielectric as well metal electrode. To investigate the effect of oxide on the switching characteristics, in this study, two devices with bilayers of IGZO/SnO2 and SnO2/IGZO were fabricated and characterized. It turns out that both unipolar and bipolar switching behaviors are dependent of the stacking sequence. This different switching behavior can be explained on the basis of the anatomy of the filament inside the switching medium. RESULT AND DISCUSSION In this study, we fabricate two types of bilayer CBRAMs with structures Ag/IGZO (10 nm)/SnO2(10 nm)/Pt and Ag/SnO2(10 nm)/IGZO (10 nm)/Pt by interchanging the stacking sequence of IGZO and SnO2 thin films. The SnO2 and IGZO thin films are deposited by RF magnetron sputtering from their respective ceramic targets on the commercially available Pt/Ti/SiO2 substrates. Finally, silver (Ag) top electrodes are deposited with the help of thermal evaporator by using a metal mask having circular holes of 100um diameter. The switching characteristics are measured using Keithley 4200 semiconductor analyzer. During all electrical characterization, the bias voltage is applied on Ag top electrode and Pt bottom electrode is kept grounded. The change in resistance from High Resistance State (HRS) to Low Resistance State (LRS) is called SET and vices versa is called RESET processes. The device Ag/SnO2/IGZO/Pt exhibited a bipolar switching characteristics with SET voltage Vset=+0.2 V and RESET voltage of Vreset=-0.4V, whereas the reverse stacking CBRAM with structure Ag/IGZO/SnO2/Pt shows a unipolar switching with SET voltages Vset=+1.7 V and -1.7V and RESET voltages Vreset= +0.7V and -0.7V . Even upto 100th sweep of both devices completely describes the switching uniformity of the devices in terms of their HRS and LRS current levels. The reverse stacking sequence results in the transition of switching from unipolar to bipolar and vice versa. The electrochemical reaction during the formation of the filament when a positive bias is applied to Ag top electrode is Ag Ag + + 1e- [ i] (oxidation) These Ag+ ions migrate through the solid electrolyte and reaches to inert metal (Pt in our study) and reduce to form Ag atom. The reduction reaction for the formation of the Ag-based filament is given below Ag+ +1e- Ag [ii] (reduction) Equations [i] and [ii] are the redox reactions which completely describe the shunting of Ag top electrode and Pt bottom electrode via the Ag filament. The complete formation of the filament with its hypothesized anatomy for the both devices is considered and the different filament structures are believed to be due to the stacking sequences of IGZO and SnO2 thin films. For example, in SnO2/IGZO stacking the filament shape is nearly conical in shape and in IGZO/SnO2 stacking the filament is formed such that the structure of the filament is a mirror image of each other along the interface horizontal axis of IGZO and SnO2 thin films. CONCLUSION In summary we fabricated two CBRAM devices with opposite stacking sequences of IGZO and SnO2 thin film by using Ag a top electrode. It is found the Ag/IGZO (10 nm)/SnO2(10 nm)/Pt showed unipolar switching and Ag/SnO2(10 nm)/IGZO (10 nm)/Pt exhibited bipolar resistive switching. We speculate that the different kinds of switching appeared as a result of reversing the stacking sequences is solely due to different filament anatomies in these devices.

A.10.5
15:30 Coffee break    
 
Thin films & interfaces II : Session chair Felix Gunkel
16:00
Authors : David Muñoz-Rojas, Viet Huong Nguyen, Ulrich Gottlieb, Anthony Valla, Bruno Masenelli, Delfina Muñoz, Daniel Bellet
Affiliations : Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France.; Univ. Grenoble Alpes, CEA, LITEN, INES, 73375 Le Bourget-du-Lac, France. ; Institut des Nanotechnologies de Lyon, INL, CNRS-UMR5270, INSA-Lyon, 69622 Villeurbanne, France

Resume : Transparent conductive oxides (TCOs) are key components of optoelectronic devices, such as solar cells or LEDs. TCOs, and in general all highly doped polycrystalline semiconductors, present high potential barriers and short depletion layers at the grain boundaries. This results in an increased probability of electron tunneling through the grain boundaries, as opposed to the thermionic emission mechanism observed in low doping semiconductors. Existing conductivity models do not properly account for charge tunneling through the grain boundaries in TCOs, which prevents a proper understanding of the scattering mechanisms limiting their conductivity. A new model is presented based on the Airy Function Transfer Matrix Method that allows the numerical calculation of charge mobility through grain boundaries in highly doped polycrystalline semiconductors.1 The new model has been used to fit experimental data obtained for Aluminum doped ZnO (ZnO:Al) samples synthesized by different methods. This has allowed the calculation of the electron trap density at grain boundaries, thus providing the dominant charge scattering mechanisms for the different samples. Our findings help to understand fundamental electrical transport mechanisms in TCOs and provide guidance on how to optimize the deposition conditions. For example, ZnO:Al thin films processed in the open air using atmospheric pressure spatial atomic layer deposition2 contain a high trap density at the grain boundaries due to trapping of oxygen species during deposition. We also show that ae simple UV treatment can enhance the conductivity of such films thanks to the light-induced de-trapping of the O species at the grain boundaries.3 References 1) Nguyen, V. H., Gottlieb, U., Valla, A., Muñoz, D., Bellet, D. & Muñoz-Rojas, D. Mater. Horizons 5, 715?726 (2018). 2) Muñoz-Rojas, D., Viet Huong Nguyen, Masse de la Huerta, C., Jiménez, C. & Bellet, D. Spatial Atomic Layer Deposition. in Chemical Vapor Deposition for Nanotechnology. Intech open 1 (2019). doi:10.5772/32009. 3) Nguyen, V. H., Bellet, D., Masenelli, B. & Muñoz-Rojas, D. ACS Appl. Nano Mater. 1, 6922?6931 (2018).

A.11.1
16:30
Authors : O. Blázquez,1,2 J.L. Frieiro,1,2 J. López-Vidrier,1,2 C. Guillaume,3 X. Portier,3 C. Labbé,3 P. Sanchis,4 S. Hernández,1,2 and B. Garrido1,2
Affiliations : 1 MIND, Department of Engineering: Electronics, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona (Spain); 2 Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Av. Joan XXIII S/N, E-08028 Barcelona (Spain); 3 CIMAP Normandie Univ, ENSICAEN, UNICAEN, CEA, CNRS, 14050 Caen (France); 4 Nanophotonics Technology Center, Universitat Politècnica de València, Camino de Vera s/n, E-46022 Valencia (Spain)

Resume : Resistive switching (RS) devices are promising for being used in memory technologies, in order to face the fast scaling demand of the electronics industry. In them, the formation and destruction of conductive filaments across a dielectric allows switching between a high resistance state (HRS) and a low resistance state (LRS). This process is triggered by a combination of the applied voltage and the injected current. Light illumination over the device can modify the potential barriers between the different layers of the device, thus influencing also over those previously mentioned magnitudes. Among the materials employed, metal oxides are widely used, being ZnO an Earth-abundant, cheap, easy to process and environmental-friendly material that, in its wurtzite structure, behaves as a transparent semiconductor with an excellent electrical and optical performance. In this work, the RS properties of ITO/ZnO/p-Si devices are studied in dark and under visible-range illumination conditions. We observed that light reduces the voltage required to induce electroforming and to switch from HRS to LRS. Since both the top electrode (ITO) and the ZnO layer are transparent to visible light, we explain this occurrence in terms of the extra free-carriers photogenerated at the p-Si substrate, allowing to achieve switching at lower voltages. Different wavelengths and optical powers were also employed, determining the corresponding dependence and permitting to optimize the parameters to obtain a light-triggered RS device.

A.11.2
16:45
Authors : A. Panepinto*, P.-A. Cormier*, D. Cossement°, R. Snyders*°
Affiliations : *Chemistry of Plasma-Surface Interactions, University of Mons, Place du Parc 20, B-7000 Mons, Belgium; °Materia Nova Research Center, Parc Initialis, Avenue N. Copernic 3, B-7000 Mons, Belgium

Resume : In this work, we study the design of a new semi-conductor material that could be implemented as photoanode in dye-sensitized solar cells (DSSCs), namely N-doped TiO2. Indeed, the conventionally used TiO2 often exhibit a too high electrical resistivity to ensure an optimal charge transport. The material has been synthesized by combining reactive magnetron sputtering (Ar/O2 mixture) and Nitrogen Ions Implantation (NII). Concerning the ion implantation process, the beam size and shape were investigated by using a Faraday cup. A systematic evaluation of the ion beam parameters such as the dose, the ion energy and the substrate angle was performed in order to study their individual effect on the morphological and crystalline properties of the films. Furthermore, the chemistry of the doped samples was probed by XPS and Tof-SIMS measurements and the results were compared to theoretical and simulations data recorded by DFT calculations and TRIDYN software, respectively. It appears that the concentration and the position of the N atoms in the TiO2 matrix mainly depend on the ion dose. Besides, we demonstrated that the O vacancies level plays a key role on the N position into the titanium oxide lattice and favor the substitutional doping.

A.11.3
17:00
Authors : Maximilian Speckbacher 1, Oliver Bienek 2, and Marc Tornow 1
Affiliations : 1 Professorship of Molecular Electronics, Department of Electrical and Computer Engineering, Technical University of Munich, Theresienstraße 90, 80333 Munich, Germany 2 Walter Schottky Institute and Physics Department, Technical University of Munich, Am Coulombwall 4, 85748 Garching, Germany

Resume : The shape, size and location of conductive filaments (CFs) in the electrolyte of electrochemical metallization cells (EMCs) are of particular interest in the framework of memory device down-scaling efforts. In this work, we report on the effect of oxide type and thickness on these characteristics in tailored nanoscale junctions, using Ag-nanocubes (AgNCs) of edge length 100 nm as active electrodes (AEs). DC IV-sweeps on single AgNCs, placed on TiO2-coated Si substrates were carried out using Conductive-Probe Atomic Force Microscopy (CP-AFM), revealing pronounced threshold switching behavior [1]. Afterwards the AgNCs were mechanically removed and the exposed oxide area scanned in CP-AFM. Clearly, formed CFs could be spatially resolved and the geometry of their cross-section at the surface analyzed in detail. Intriguingly, a pronounced Ag material accumulation can be observed in particular below the AgNC side-facets and edges, as further supported by cross-sectional SEM studies. This can be assigned to electric field enhancement at these locations, as confirmed by finite element simulations. By systematically increasing the TiO2 layer thickness from 2 nm to 20 nm, a trend to increasingly more material being deposited in the oxide film is observed. We anticipate that indeed, the increased time duration for filament formation in thicker oxides can explain this finding. We finally compare and discuss this system to AgNCs positioned on Al2O3 as reference electrolyte, where mostly bipolar memory switching with different filament shapes can be observed. [1] M. Speckbacher, M. Rinderle, W. Kaiser, E. Osman, D. Chryssikos, A. Cattani-Scholz, J. M. Gibbs, A. Gagliardi and M. Tornow, Adv. Electr. Mat. (accepted, 2019)

A.11.4
17:15
Authors : M. J. Sánchez 1*, C. Ferreyra 2, W. Román Acevedo2, R. Gay3 and D. Rubi2
Affiliations : 1 INN- Centro Atómico Bariloche and Instituto Balseiro, 8400 San Carlos de Bariloche, Argentina; 2 GIyA and INN, CNEA, Av. Gral Paz 1499 (1650), San Martín, Buenos Aires, Argentina; 3CIC nanoGUNE, Tolosa Hiribidea 76, 20018 Donostia-San Sebastián, Spain. *Corresponding author Email: majo@cab.cnea.gov.ar

Resume : Redox-based memristive devices are among the alternatives for the next generation of non volatile memories, but also candidates to emulate the behavior of synapses in neuromorphic computing devices. It is nowadays well established that the motion of oxygen vacancies (OV) at the nanoscale is the key mechanism to reversibly switch metal/insulator/metal structures from insulating to conducting, i.e. to accomplish the resistive switching effect. The control of OV dynamics has a direct effect on the resistance changes, and therefore on different figures of memristive devices, such as switching speed, retention, endurance or energy consumption. Advances in this direction demand not only experimental techniques that allow for measurements of OV dynamics, but also of theoretical studies that shed light on the involved mechanisms. Along this goal, we analize the OV dynamics in redox interfaces formed when an oxidizable metallic electrode is in contact with the insulating oxide. We show how the transfer of OV can be manipulated by using different electrical stimuli protocols to optimize device figures such as the ON/OFF ratio or the energy dissipation linked to the writing process. Analytical expressions for attained resistance values, including the high and low resistance states are derived in terms of total transferred OV in a nanoscale region of the interface. Our predictions are validated with experiments performed in Ti/La1/3Ca2/3 MnO3 redox memristive devices. Reference: Ferreyra et al., eprint arXiv:1811.09528 (2018).

A.11.5
18:00 Graduate Student Awards Ceremony & Reception 18:00-21:00 (Main Hall)    

No abstract for this day


Symposium organizers
Elisa GILARDI Paul Scherrer Institute (PSI)

Forschungsstrasse 111, 5232 Villigen – PSI, Switzerland

elisa.gilardi@psi.ch
Federico BAIUTTICatalonia Institute for Energy Research (IREC)

Jardins de les Dones de Negre 1, 08930 Barcelona, Spain

fbaiutti@irec.cat
Felix GUNKELRWTH Aachen University & Peter Grünberg Institute, Forschungszentrum Jülich

Peter Grünberg Institute (PGI-7), Forschungszentrum Jülich, 52425 Jülich, Germany

f.gunkel@fz-juelich.de
Matjaz SPREITZERJozef Stefan Institute Ljubljana

Jamova cesta 39, 1000 Ljubljana, Slovenia

matjaz.spreitzer@ijs.si