Nanomaterials - electronics & -photonics

Resume : Nanomembranes are thin, flexible, transferable and can be shaped into 3D microtubular NEMS architectures. This makes them attractive for a broad range of applications and scientific research fields ranging from novel hybrid heterostructure devices to ultra-compact 3D systems both on and off the chip. If nanomembranes are differentially strained they deform themselves and roll-up into microtubular NEMS structures upon release from their mother substrate. Rolled-up nanomembranes can be exploited to rigorously compact electronic circuitry and energy storage units. They can also serve as ideal platform to study novel photonic and plasmonic phenomena. As rolled-up microtubes can be easily tuned into the size range of single cells, they are perfectly suited to study single cell behaviour in 2D confined systems and establish exciting environmental and biomedical applications such as biomimetic regenerative cuff implants or ultra-sensitive yet fully integrative lab-in-a-tube systems. If magnetic tubes or helices are combined with spermatozoa, such hybrid micro-biorobotic motors offer new perspectives towards paradigm shifting reproduction technologies.

Resume : Although Chemical vapor deposition (CVD) is a good technique to synthesize large area 2D materials i.e. Graphene, MoS2 but boundaries between the grains, defects and grain size of these materials have great influence on the electronic and mechanical properties.[1] Usually these 2D synthesized materials are polycrystalline where scattering of charge carriers at grain boundaries can lead to degradation of its performance, compared to exfoliated single-crystal graphene or other TMDs.[2] The electrical properties of grain boundaries have so far been addressed indirectly without direct knowledge of their locations. Previously, we present a technique to measure the electrical behavior of individual grain boundaries imaged with the help of aligned liquid crystal.[3,4] Unexpectedly, the electrical conductance was degraded by three orders of magnitude for grain boundaries with the least on/off ratio. Here we studied the effect of UV exposure on aligned LC on graphene and observed p-type doping in the electrical properties. Interestingly on removal of LC, the doping effect can be removed as well and Dirac point could shift to its original state. We believe that LC alignment approach is versatile to alter the electrical properties of graphene and other TMDs based devices. Our study suggests a useful technique to fabricate devices on a single crystal area, using optimized growth conditions and device geometry. References: 1. Yazyev, O. V.; Louie, S. G. Nature Materials 2010, 9, (10), 806-809. 2. Huang, P. Y.; Ruiz-Vargas, C. S.; van der Zande, A. M.; Whitney, W. S.; Levendorf, M. P.; Kevek, J. W.; Garg, S.; Alden, J. S.; Hustedt, C. J.; Zhu, Y.; Park, J.; McEuen, P. L.; Muller, D. A. Nature 2011, 469, (7330), 389-+. 3. Shehzad, M. A.; Hussain, S.; Khan, M. F.; Eom, J.; Jung, J.; Seo, Y. Nano Research 2016, 9, (2), 380-391. 4. Shehzad, M. A.; Tien, D. H.; Iqbal, M. W.; Eom, J.; Park, J. H.; Hwang, C.; Seo, Y. Scientific Reports 2015, 5.

Resume : Spintronics is a paradigm focusing on spin as the information vector. Ranging from quantum information to zero-power non-volatile magnetism, the spin information can be also translated from electronics to optics. Several spintronics devices (logic gates, spin FET, etc) are based on spin transport in a lateral channel between spin polarized contacts. We want to discuss, with experiments in support, the potential of graphene for the transport of spin currents over long distances in such types of devices. We will present magneto-transport experiments on epitaxial graphene multilayers on SiC [1]. The measured spin signals are in the mega-ohms range, and the analysis of the results in the framework of drift/diffusion equations leads to large spin diffusion length in graphene in the 100 microns range. The high spin transport efficiency of graphene can also be acknowledged up to 75% in our devices. These results will be compared to previous studies on carbon nanotubes and to our on-going study on large scale CVD grown graphene making use of h-BN tunnel barriers [2]. Our latest results of spin precession in graphene channels obtained at room temperature will be also discussed. A unified picture of spin transport in nanotubes and graphene will be presented [3]. [1] B. Dlubak et al. Nature Physics 8, 557 (2012). [2] M. Piquemal-Banci et al. Applied Physics Letters 108, 102404 (2016) [3] P. Seneor et al. MRS Bulletin 37, 1245 (2012).

Resume : Graphene, a one-atom-thick layer of carbon atoms, is a great material for studying the atomic structure of defects, their dynamics, and the correlation between the exact disorder structure and macroscopic properties. From the technological point of view, purposefully created defects can be used to control many of the properties of this material, which can lead to new applications in a variety of different fields. However, to do this in a controlled manner, very good control over the created defects is needed. One way to achieve this is to use energetic particles to introduce defects and to study in detail the resulting atomic structure. While this has been attempted to some extend, most of the structural analysis has relied on indirect spectroscopic data. In this presentation, I will present an enhanced theoretical model to describe electron beam knock-on damage in graphene with a high enough predictive power to determine isotope ratios from experimental graphene samples, describe large scale structural modification of graphene using electron and ion irradiation, as well as present results on implantation of foreign atoms into the graphene lattice using low-energy ions. Finally, the expected and observed changes that these structural manipulations have on the electronic properties of graphene will be discussed.

Resume : Understanding of interface effects in organic thin film transistors (OTFT) is key to realize high performance organic flexible electronics and organic sensor applications. OTFT exploit field effect to accumulate charge carriers into an almost 2D confined layer adjacent to the interface with the gate dielectric. Charge carrier density and transport in this channel depend not only on intrinsic semiconductor properties but can be largely tuned by interactions stretching across the semiconductors interfaces. Here we investigate interface effects in thin films containing pentacene and C60 as model compounds for organic electronics devices. Films of pure semiconductor and heterojunctions are grown by vacuum sublimation and their electrical properties are studied in-situ starting from the submonolayer regime. Displacement current measurements and temperature dependent transfer measurements are employed to quantify carrier density, mobility and trap levels as a function of layer thickness and morphology. Our findings provide quantitative descriptions for (i) charge density increase in submonolayer films [1]; (ii) charge transfer across the interface in heterojunctions [2] and (iii) band broadening due to interfacial disorder; [1] T. Cramer, A. Kyndiah, A. Kloes, M. Murgia, B. Fraboni, and F. Biscarini, Phys. Rev. B, vol. 91, no. 20, pp. 1?7, 2015. [2] A. Kyndiah, T. Cramer, C. Albonetti, F. Liscio, S. Chiodini, M. Murgia, and F. Biscarini, Adv. Electron. Mater., vol. 1, no. 11, p. 1400036, 2015.

Resume : Increasing attention is paid nowadays to the elaboration of cost-effective technologies of material nanostructuring for nanoelectronic and photonic applications. In this paper, we report on a novel approach, called Surface Charge Lithography (SCL), allowing direct writing of gallium nitride micro- and nanostructures. Note that GaN is presently the second most important semiconductor after Si. The proposed technological route comprises low-dose focused ion beam (FIB) direct writing of micro-nanostructures and subsequent photoelectrochemical (PEC) etching. The low-dose FIB treatment induces surface negative charge which shields the semiconductor material against PEC etching. Under specific conditions, SCL proves to be a powerful tool for the fabrication of ultrathin GaN suspended membranes which are promising for nanoelectronic applications, in particular in high-power memristive devices [1]. Besides, we demonstrate that SCL provides conditions for the fabrication of GaN ultrathin membranes nanoperforated in an ordered fashion [2]. The development of flexible photonic crystals with embedded waveguides, beam splitters and cavities is reported and the results of modelling of their characteristics are presented. We show also that PEC etching of bulk GaN enables one to fabricate self-organized three-dimensional nanostructured architectures [3]. Results of systematic characterization of the morphology, crystalline quality, electronic and photonic properties of nanoscale-thick gallium nitride membranes along with examples of their practical applications are discussed. [1] M. Dragoman, I. Tiginyanu, D. Dragoman et al., Memristive GaN ultrathin suspended membrane array. Nanotechnology 27, 295204 (2016); [3] O. Volciuc, V. Sergentu, I. Tiginyanu et al., Photonic crystal structures based on GaN ultrathin membranes. J. Nanoelectron. Optoelectron. 9, 271-275 (2014); [3] I. Tiginyanu, M. A. Stevens-Kalceff, A. Sarua et al., Self-organized three-dimensional nanostructured architectures in bulk GaN generated by spatial modulation of doping. ECS J. Solid State Sci. Technol. 5, P218-P227 (2016).

Resume : Photonic crystals (PCs) control light propagation via a photonic band gap, originated when a periodic lattice of alternating refractive index (n) is present. A higher n contrast between the periodic nodes and imbedding medium produces better photonic properties, but the fabrication of large area, homogeneous and high quality PCs is complex due to the poor processability of high-n materials. Transition metal dichalcogenides (TMDs) have a high n (n>3) through the visible and near-infrared spectrum, making them promising for visible light PCs. However, the production of TMD-based PCs is limited by complex chemical interactions in high-resolution etching which reduce the resolution or completely destroy the material. We have developed a new method that does not require the direct etching or processing of TMD to produce TMD-based PCs. The PC structure is etched into quartz (n~1.5), then the TMD is conformally deposited using atomic layer deposition (ALD) to produce a high efficiency PC, The fabricated PC shows intense resonances due to the high n-contrast between the TMD film and the quartz substrate. Moreover, we show that changing the feature size and the thickness of the PC layer can modulate these resonances significantly. This is a new class of 3-D photonic crystal which is simple to fabricate, but produces large optical modulations.

Resume : Two-dimensional molybdenum disulfide (MoS2) which is one of the most promising candidates for realizing monolayer (~ 0.65 nm) applications in opto- and nanoelectronics has attracted great interests due to its an excellent transparency in the visible wavelength range, mechanical stiffness, flexibility, and electrical carrier mobility. To meet the growing demand for large-area electronics, synthetic fabrication and electrode patterning methods to produce a large-area monolayer MoS2 semiconductors and contacts, respectively are highly desirable. In this regard, we report the first demonstration of large-area monolayer MoS2 FETs with inkjet-printed Ag source/drain (S/D) electrodes. The monolayer MoS2 film was grown by a chemical vapor deposition (CVD) method, and the top-contact Ag S/D were deposited onto the films using a low-cost drop-on-demand inkjet-printing process without any masks and surface treatments. The electrical characteristics of FETs were comparable to those fabricated by conventional deposition methods such as photo- or electron beam lithography. The contact properties between the S/D and the semiconductor layer were also evaluated using the Y-function method and an analysis of the output characteristic at the low drain voltage regimes. Furthermore, the electrical instability under positive gate-bias stress was studied to investigate the charge-trapping mechanism of the FETs. CVD-grown large-area monolayer MoS2 FETs with inkjet-printed contacts can provide an attractive approach for realizing large-area and low-cost thin-film electronics.

Resume : The optical Kerr effect is a nonlinear process present in all materials with applications in domains such as fiber optics communications or integrated photonics. However, it is difficult to find materials with high nonlinear optical properties at telecom wavelengths and high thermal and chemical stability. InN, with band-gap energy in this spectral range, stands out in this field. A simple way to measure the Kerr effect is the z-scan technique, proposed by Sheik-Bahae group in 1990. In this technique, the sample is placed between two achromatic lenses to firstly focus a high peak-power laser beam on the sample and then collimate it to measure the transmitted intensity. The sample transmittance is recorded as a function of its position along the optical axis. This paper presents measurements of the saturable absorption and Kerr effect coefficients in 1-µm-thick InN layers. A mode-locked fiber laser with 200 fs pulses, 4 MHz repetition rate, and 30 mW average power has been used as excitation source. When focused, the laser beam has a Gaussian waist of ?0 ~ 20 µm, a Rayleigh length of z0 ~ 0.5 mm, and a maximum peak intensity of I0 ~ 18 GW/cm2. From z-scan measurements, we estimate a very high nonlinear absorption coefficient of ?2 = 1800 cm/GW and a Kerr coefficient of n2 = 1.5·10-2 cm2/GW. Thus, we can conclude that InN attains nonlinear optical properties suitable for applications at 1.5 µm.

Resume : In the last decade, various techniques have been proposed for synthesizing one-dimensional nanostructures such as nanowires (NWs) and nanobelts. In particular, monoclinic gallium oxide (beta-Ga2O3) has received considerable attention for use in NWs owing to its wide bandgap of 4.9 eV, high breakdown field (> 8 MV/cm), and high optical transparency to visible and ultraviolet radiation. Recently, applications of beta-Ga2O3 NWs in optoelectronic and photonic devices, as well as gas sensors, have been widely explored. Moreover, doped beta-Ga2O3 NWs have attracted even greater interest as doping is an effective way to tune the physical properties of such structures. Many of these efforts have focused on demonstrating the performance of NW-based devices by varying the types and concentrations of the doping elements used, with Eu, Cr, Mn, Sn, and In having been examined. Among them, In is regarded as a promising dopant for significantly enhancing the sensitivity and quantum efficiency in nanobelt-based photodetectors, as initially demonstrated by Tian et al., who demonstrated that doping with In atoms increased the carrier density and mobility of Ga2O3 NWs compared to those of their undoped form. The performance of these photodetectors was comparable or superior to that of other one-dimensional semiconductor-based photodetectors. The synthesis of In-doped beta-Ga2O3 NWs is typically carried out by thermal evaporation and vapor transport, using a mixture of either In and Ga2O3 powders or Ga and In2O3 powders as source materials. Recently, we reported the growth of beta-Ga2O3 NWs using radio frequency (RF) powder sputtering. The deposition of non-stoichiometric Ga2O3-x under an oxygen-deficient atmosphere was essential for facilitating the growth of beta-Ga2O3 NWs by a self-catalytic vapor-liquid-solid (VLS) process using self-assembled Ga seeds. In this work, we examine the growth mechanism of In-doped beta-Ga2O3 NWs synthesized by powder sputtering. In particular, the role of In atoms in determining the growth mechanism and the structure of NWs is investigated. Finally, by examining the evolution of surface morphologies as a function of sample thickness, a growth scenario of the In-doped beta-Ga2O3 NWs is proposed.

Resume : We will report the theoretical results on a layered scandium dioxide (ScO2). Density functional theory calculations under the generalized-gradient approximation with on-site Coulomb interactions (GGA + U) were performed to investigate the stability, electronic and magnetic properties of 2D ScO2. The calculated results find the so-called T-phase to be a non-magnetic wide-band gap semiconductor, and the H-phase monolayer is an antiferromagnetic (AFM) Analysis of the chemical topology shows that the Sc?O bonds are highly ionic in character. Furthermore, T- and H-phase bilayers respond differently to strain applied normal to the material surface; for the former, the band gap increases and then decreases with the increase of tensile strain, whereas the latter shows a metal - semiconductor - metal transition as a larger tensile strain is applied. The versatility of the electronic properties of ScO2 in its different phases and forms (monolayer and bilayer) can thus be exploited in devices at the nanoscale.

Resume : Biodigital devices are emerged an interdisciplinary field of research in the biosensors and bioelectronics [1, 2]. Today, smart bio-interfaces are applying a renewed influence on bioelectronics beyond the incorporation of few or single atom(s)-thick two dimensional (2D) materials, which fuses the benefits of extraordinary stimuli-controlled interior and exterior catalytic atomic surfaces with those of super-thin digital biotechnology [3, 4]. The development of switchable and/or tunable interfaces of 2D materials endowed with desirable functionalities, and incorporation of these interfaces into on/off-switchable bio-devices [5]. The aim of talk is to demonstrate various strategies of stimuli-enabled programming of enzymatic super-thin digital systems answer by a considerable control in their biochemical behavior with uni- and multi-model triggering of interfaces via temperature, pH, light, etc. These smart bioengineered atom-thick approaches are being formulated that sense specific biochemical changes and regulate in a liable manner, making them useful super-thin biotechnological tools. The progress in this field would make significant contributions to new age biodigital energy and medical technologies. References 1. Tiwari, A.; Turner, A. P. F. (Eds.), In Biosensors Nanotechnology, Wiley - Scrivener, USA, MA, 2014. 2. Parlak, O.; Beyazit, S.; Jafari, M. J.; Bui, B. T. S.; Haupt, K.; Tiwari, A.; Turner, A. P. F. Advanced Materials Interfaces, 2015. 3. Parlak, O.; Turner, A

Resume : Stable 2D semiconducting oxide of tungsten and molybdenum has been investigated widely and utilized for several applications. MoO3 2D nano-fakes are found to be of particular interest due to their potential applications. MoO3 nano-fakes have been used for photoluminescence and field emission applications. Bulk MoO3 has been successfully used in organic electronic devices such as organic light emitting diodes (OLEDs) and organic photovoltaics as a hole injection and extraction layer, where the semiconducting properties of MoO3 has improved the efficiencies of these devices significantly. Moving from bulk to 2D nano-fakes is expected to improve the crystalline structure of MoO3, which thereby is expected to improve the semiconducting properties. In continuation to our earlier published work, advantage of 2D materails motivated us to utilize the 2D MoO3 nano-fakes as the hole injection layer (HIL) in OLEDs. Here, to observe the effect of solar illumination on the properties of 2D MoO3 nano-fakes, OLEDs with nano-fakes as the HIL exposed for different durations have been fabricated and their effects on device characteristics are discussed. Nano-fakes irradiated for 0, 15, 30, 45, 60 and 120 min with solar power were used for this study, and the device results with nano-flakes as the HIL were compared with that with bulk MoO3 as the HIL.

Resume : Etching of silicon is the basic technology step for a large variety of MEMS, NEMS and microfluidic applications. Even the fabrication of large area nanostructure in polymers starts in our examples with lithography and etching of silicon. After a short introduction to DTU Danchip (Clean Room), the talk will focus on plasma etching of silicon in detail. The plasma chemistry and physics during silicon etching poses challenges and opportunities, which will be demonstrated using examples reaching from nanopillars for SERS enhancement to X-ray compound lenses. A short excursion into Atomic Layer Deposition and some results on structures realized with this very versatile technology will be presented and accordingly discussed. References: 1. Advanced Materials 24, 2012, OP11-OP18 2. Microelectronic Engineering 141, 2015, 6-11 3. Optical Materials Express 5, 2015, 2804-2811

Resume : In the last decade, terahertz technology has attracted attention of researchers and scientists because of its unique properties. Developing reliable sources and detectors are the most prominent part of terahertz technology. Photoconductive antennas are the most common devices for terahertz wave generation and detection due to its compact structure, simple fabrication, room temperature operation and broadband pulse nature. Despite of all advantages, antenna's low output power is the most challenging issue that has to be overcome. In this paper, a photoconductive terahertz source based on periodic nano-plasmonic structure has been introduced, simulated and fabricated. Terahertz power improvement was achieved by periodic nanostructures on the active part of the device. By using finite difference time domain (FDTD) method, periodic gold nanodisk structure has been simulated and optimized for 800 nm femtosecond laser pulse. Laser optical power reflection reduced from 32% for conventional PCA to less than 1% for the designed nanostructure-based antenna. The photocurrent increased more than 100%. Optimized antenna was fabricated on LT-GaAs wafer using photolithography and electron beam lithography methods. Terahertz time domain spectroscopy (THz-TDS) test system confirmed the simulation results and showed output terahertz power improvement.

Resume : Recently, transparent heaters require good flexibility and stretchability as the parts of wearable electronics since future smart devices have irregular shapes and arbitrary curved surfaces. Those transparent and stretchable heaters can be applied to diverse areas such as defogging a window, outdoor cooking, and thermal therapy. Although indium tin oxide (ITO) has been widely used as the transparent resistive heater due to its good optoelectronic properties, it has limitations due to its fragility. In addition, the wireless operation becomes essential for the wearable electronics. Here, we demonstrate a large-area transparent and stretchable heater on various substrates based on Joule heating using the random network of the ultra-long Ag nanofibers (AgNFs). Optical transmittance and the sheet resistance of electrode can be controlled by adjusting area fraction of AgNF random networks. Therefore, various temperature range and power consumption can be achieved by varying density of AgNFs. AgNFs heater shows high temperature (250 ºC) at relatively low operating voltage (5.5 V) and excellent temperature reliability under large strain (30%). In addition, we integrated wireless operation system and AgNFs heater. Bluetooth module and the micro-controller unit are connected to AgNFs heater so that temperature can be controlled directly using smart devices. We believe these stretchable and transparent large-area heaters with the wireless operation systems can be embedded into future wearable electronic devices.

Resume : Two-dimensional (2D) layered materials (such as hexagonal boron nitride (hBN) and graphene) bring a new function into nanodevices and flexible electronics due to their excellent mechanical properties. HBN, sometimes referred as ?white graphene?, is a dielectric with a high electrical resistance and a wide bandgap of ~5.9 eV together with chemical inertness and high thermal conductivity, suggesting a myriad of applications in nanodevices ranging from field-effect tunneling transistors, capacitors, to hydrogen storage. Resistive switching memory (RSM) is considered one of the most promising candidates for next generation memory due to its excellent storage capability and scalability down to less than 10 nm. High-performance RSM with excellent mechanical flexibility is of great interest for the future smart wearable electronics. However, conventional switching materials of ceramic dielectric thin films often suffer from detachment from substrates and cracking under repetitive bending, becoming a bottleneck in realizing a highly flexible RSM. In this work, the ultrathin (~ 3 nm) hBN, is synthesized via chemical vapor deposition (CVD) for the fabrication of flexible RSM. The hBN-based RSM features good switching endurance (? 550 cycles), long retention time (? 3000 s) and acceptable memory window (? 100). Especially, the memory device can operate under extreme bending conditions (bending radius, 7 mm) without large variation of memory window, even after 750 bending cycles. Due to the transferable property of hBN like graphene film, the fabrication of transferable hBN-based RSM is promising on any desired arbitrary substrate. This work exploits and broadens the applications of 2D hBN nanomaterial for use as flexible RSM which would be useful in integrated epidermal electronics in future.

Resume : In recent years, molybdenum disulfide (MoS2) based short-wave optoelectronic devices have drawn a great interest of the scientific communities due to its large direct bandgap in very low dimensions as compared to its bulk counterpart. Researchers have reported several devices using either mechanically exfoliated, or chemically or CVD-grown 2-D mono/multi-layer MoS2 based devices, although the wafer scale device production with very good output performance has not been achieved yet. Therefore, it is desirable to fabricate low-cost and high-responsive devices operating at low powers for better performance. Here, we report the novel MoS2 colloidal quantum dot based photodetector device which exhibits good optical responsivity and detectivity compared to the commercial Si based visible photodetector. The use of colloidal nanocrystal (NC) of 2D materials can be an excellent approach for large area device fabrication as well as a flexible detector with enhanced output due to its excellent light absorbing property of MoS2 NCs and short carrier diffusion path. Moreover, the size-dependent optical characteristics, allowed us to select the desired spectral detection at the time of fabrication by controlling the crystal size, which makes them a potential candidate for tunable optical devices. We have also investigated the potentiality of different sized MoS2 NCs for a wide spectral range using COMSOL simulation based on FEM study which also exhibits the size dependent electric field enhancement and our theoretical predictions matched with the experimental results very well. The current-voltage characteristics and pulsed illumination of all devices have been investigated and reported. Our work demonstrates the great potentiality of the MoS2 NCs based flexible devices where the NCs have been used as the key component for their high performance, low-cost, ease of fabrication and their size-tunable band gap, in the optoelectronic integrated circuits.

Resume : The FePt L10 structure is characterized by a tetragonal distortion of a few percent along the c-axis, accompanied by an alternating stacking of elemental layers along the [001] direction. By means of density functional theory (DFT) calculations, within the pseudopotential plane wave method as implemented in VASP (Vienna Ab initio Simulation Package). The projector augmented wave method with exchange correlation function is used for spin polarized generalized gradient approximation (GGA). We have determined structural, electronic, and magnetic properties of perfect surfaces (9, 11, 13 plans) and with stacking defect. Magnetic properties are determined by: (1) direct Fe-Fe interactions between an Fe atom and its four nearest neighbors in the Fe layer (2.92µB), and (2) polarization driven ?indirect? Fe-Pt-Fe interactions (3.03 µB).

Resume : Atomic clusters have attracted a lot of attention, and are still a matter of intense research, because of their unique combination of molecular and condensed matter physics. Of particular interest, are the binary clusters composed bimetallic transition metal (TM) clusters with physical and chemical properties. Our investigations are based on spin-polarized density functional theory (DFT) as implemented in the Vienna ab initio simulation package (VASP), with the spin polarized generalized gradient approximation (GGA). The calculations are performed on pure Con and ConCr (n=1-5) clusters, we address how Cr-doping affects the structure, how the binding energy is as compared with the pure clusters, and how electronic properties such as the ionization potential, electron affinity, dissociation energy and magnetic moment, are modified.

Resume : An Al2O3 thin films for the purpose of barrier layer against environmental moisture was prepared by means of atomic layer deposition (ALD) method. Moisture in the air is known to be the most responsible element which makes the organic based device unusable. Because most of organic materials are weak at high temperature the thin film process temperature should be maintained as low as possible. To achieve high quality barrier characteristics TMA, TiCl4, H20 were used as precursors and reactant gas and each process conditions were carefully controlled. The Al2O3/TiO2/Al2O3 multilayer thin film was then deposited on PEN substrate. The barrier performance was examined by acquiring a water vapor transmission rate (WVTR) of the thin films.

Resume : The two-dimensional materials (2D) are attracting increasing attention due to their unique properties and potential use in both nano- and opto-electronics. In such applications, the electronic transport properties of 2D materials are particularly important. In this communication, a new insight into these properties is presented by studying the so-called complex band structures (CBSs) of the selected 2D materials (graphene and transition metal dichalcogenide monolayers). We show that the CBSs analysis allows to describe a crucial transport-related phenomena, such as the tunneling currents, electronic state localization, or even the Fermi level pinning in metal-semiconductor junctions. A generalized efficient theoretical method for solving such class of problems is presented and gives a complete set of physically relevant solutions. These solutions are characterized and classified into propagating and evanescent (localized) electronic states, where the latter states present not only monotonic but also oscillatory decay character. Furthermore, the importance of CBS’s for transport processes is additionally reinforced by demonstrating their direct use in the ballistic quantum transport calculations across 2D materials, by using the phase field matching theory.

Resume : Topological insulators (TIs) have generated a great interest in the fields of condensed matter physics, chemistry and materials science. A topological insulator is a material that is electrically insulating in the bulk, while possessing highly conductive and spin-polarized massless Dirac surface states that are protected against disorder by time-reversal symmetry (TRS), allowing for near dissipation-less transport of spin on the surface[1]. The TRS can be broken by, for example, using elemental doping to induce a magnetic phase in the material. The broken time-reversal symmetry allows for the formation of an energy gap on the surface and is important for many interesting properties in these materials [2]. The second generation 3D Tis Bi_2 Se_3 and Bi_2 Te_3 are a class of such materials. To enable a multitude of possible applications of these materials, it is necessary to open a surface energy gap as well as keep the Fermi energy inside the bulk gap [3]. It has been proposed in the literature that doping TIs by magnetic transition metals, such as Fe, Mn, Cr and Co, could break the TRS and open a surface gap [4]. The binary compound Bi_2 Se_3 is very popular compound for TI studies as it has a relatively large bandgap ( ̴ 0.3 eV) compared with other TIs. Transition metals, such as Fe, Cr, Mn, and Cu have been widely substituted into bulk Bi_2 Se_3 to produce magnetically manipulated topological semiconductors [5]. One attractive direction in the research is the use of nanostructures, wherein the ratio of surface area to volume is much higher than in bulk materials so that the total conduction from the bulk region is lower, allowing observation of the surface states in certain transport measurements. In the present study, we synthesized Co-doped Bi_2 Se_3 nanoplates by solvothermal reaction. The as-synthesized nanoplates show uniform hexagonal morphology of about 1 μm size and ~ 30 nm thickness. A physical property measurement system (PPMS) is used to determine the temperature dependent magnetization in zero-field cooled and field-cooled cycle between 5 K and 300 K. The doped nanoplates are found to be paramagnetic in the whole temperature range, in disagreement with the existence of a diamagnetic to paramagnetic phase transition at 12 K in Co-doped Bi_2 Se_3 single crystals. Further experimental and computational studies of electronic and magnetic properties of the system are under way. References: [1] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045 (2010). [2] J. Wang, X. Chen, B.-F. Zhu, and S.-C. Zhang, Phys. Rev.B 85, 235131 (2012) [3] X. L. Qi, T. L. Hughes, and S. C. Zhang, Phys. Rev. B 78, 195424 (2008) [4] Q. Liu, C. X. Liu, C. Xu, X. L. Qi, and S. C. Zhang, Phys. Rev. Lett. 102, 156603 (2009). [5] Y. S. Hor, A. J. Williams, J. G. Checkelsky, P. Roushan, J. Seo, Q. Xu, H.W. Zandbergen, A. Yazdani, N. P. Ong, and R. J. Cava1, Phys. Rev. Lett. 104, 057001 (2010).

Resume : Photoresponsive organic field-effect transistors (Photo-OFETs) and Photodiodes have been widely investigated because of their attractive advantages such as large-area, flexibility, and processing versatility [1-3]. Single organic layer, organic planar heterojunctions and bulk heterojunctions thin film are widely used in phototransistors [4-5]. Nevertheless, the photoresponsivity of single organic layer photo-OFETs is generally low due to the relatively low charge carrier mobility of the active semiconductor layer and poor exciton dissociation efficiency. In this study, we present on the fabrication of phototransistors with a novel multilayer organic planar junction structure, in which the photo excitons generation and dissociation are realized mainly in all the organic semiconductor layers P3HT/CuPc/P3HT, while the transport of charge carrier current occurs in high mobility channel layer based on P3HT. We fabricated P3HT/CUPC photo-OFETs on glass substrates. The electrodes were etched with standard photo lithography to produce interdigitated source-drain electrode fingers with a channel length of 100 µm and a channel width of 60mm. Three different device structures was fabricated in this study and named as D1, D2, D3, configurations are given below; D1: Au (S-D)/P3HT(100nm)/PMMA(600nm)/Al(gate), D2: Au (S-D)/CuPc(10nm)/P3HT(100nm)/PMMA(600nm)/Al(gate), D3: Au (S-D)/P3HT(100nm)/CuPc(10nm)/PMMA(600nm)/Al(gate), Table 1: Device performance details Devices R (mA/W) Max. value of P Vth µDark (cm2/Vs) µLight (cm2/Vs) D1 14.25 (VG=-40V) 5.95 x 10^2 -7.5 0.002 0.002 D2 34.74 (VG=-40V) 2.1 x 10^3 -5.11 0.0015 0.0014 D3 11.58 (VG=-40V) 1.3 x 10^3 0.62 0.00028 0.00024 References: 1) Y. Chu, X. Wu, J. Lu, D. Liu, J. Du, G. Zhang, J. Huang, Adv. Sci. 1500435 (2016). 2) Z. A. Kösemen, A. Kösemen, S. Öztürk, B. Canımkurbey, S. E. San, Y. Yerli, A. V. Tunç, Microelectronic Engineering 161, 36–42 (2016). 3) Y. Li, W. Lv, X. Luo, L. Sun, F. Zhao, J. Zhang, J. Zhong, F. Huang, Y. Peng, Organic Electronics, 26, 186-190 (2015). 4) Y. Guo, G. Yu, Y. Liu, Adv. Mater., 22, 4427–4447, (2010). 5) J.G. Labram, P.H. Wökenberg, D.D.C. Bradley, T.D. Anthopoulos, Org. Electron., 11, 1250–1254 (2010).

Resume : Bimetallic systems of Au-Ag nanostructures were synthesized within the channels of amine modified mesoporous SBA-15 by post modification. It was found that the mesoporous channels effectively controlled the changes in the size and morphology of the embedded nanoparticles from spherical (6-8 nm) to rod shape (aspect ratio ~15-20 nm) with variation in the amount of bimetallic (Au and Ag) loading. The change in the color of the prepared materials from white for bare SBA-15 to deep purple for Au-Ag (10:1) loading and dark brown for Au-Ag (1:10) loading established the inclusion of metals within the mesoporous sieves. EDX and elemental mapping studies confirmed the presence of Au and Ag nanospecies within/on the surface of silica hosts. DRS studies showed the presence of single plasmon band for various bimetallic Au-Ag loadings illustrating the alloy structure/nature of NPs with homogeneous composition. TEM micrographs depicted discrete bimetallic nanostructures uniformly distributed and stabilized within/on the surface of mesoporous host. Moreover, surface area was significantly reduced from 694 m2g-1 for bare SBA-15 to 484 and 533 m2g-1 for Au-Ag (1:10) and Au-Ag (10:1) loading respectively due to partial blocking of mesopores with increased bimetallic impregnation. The prepared bimetallic composites also exhibited unprecedently high catalytic activity due to the combined tuning of high particle dispersion and enhanced synergy. Among all bimetallic nanocomposites, Au-Ag (5:1)/m-SBA-15 nanocomposites exhibited the best catalytic activity (k= 2.12×10-2 min-1 and 3.99×10-2 min-1) in comparison to other bimetallic and monometallic Au/m-SBA-15 and Ag/m-SBA-15 nanocomposites for the selective reduction of nitrobenzene to aniline and p-nitroacetophenone to p-aminoacetophenone respectively.

Resume : Half-metallic ferromagnets (HMFs) have attracted considerable attention due to their potential use as a highly spin-polarized current source in spintronics. Among some kinds of HMFs, Co-based full Heusler alloys are of particular interest due to comparatively high Curie temperatures. For applications, not only a high Curie temperature and high spin polarization but also high stability of the L21 phase is desired. In the present work, a mixture of elemental Co50Mn25Al25 powders has been subjected to mechanical alloying (MA) to prepare the Heusler Co2MnAl magnetic alloys. It is found that nanocrystalline Co2MnAl alloys with a grain size of 80 nm can be produced from a mixture of elemental Co50Mn25Al25 powders by MA for 5 hours coupled with subsequently annealed at 700C. The X-ray diffraction and magnetic data have been discussed simultaneously in order to achieve a better understanding of the solid state reaction induced by MA. Acknowledgements This work is financially supported by the Ministry of Knowledge Economy (MKE) of Korea.

Resume : The method of nanosecond pulsed laser ablation in liquid environment is employed to produce nanostructures. The disc-shaped barium hexaferrite ablation target is fabricated by sol-gel auto-combustion and embedded in double distilled water during the experiment. The ablation procedure is performed by a Nd:YAG laser system. Different colloids are fabricated by variation of the laser wavelength and fluence. Their influence on the morphology of the nanostructures produced is investigated. The fundamental (? = 1064 nm), second (? = 532 nm), third (? = 355 nm) and fourth (? = 266 nm) harmonic and fluence changed from several J/cm2 to tens of J/cm2 are used at the experiments. The effectivity of the ablation procedure is estimated by the optical transmission of the colloids in the near UV and visible regions. The shape of the nanostructures and their size distribution are visualized by using TEM analysis. XRD, SAED and HRTEM are applied to examine the material phases of the nanostructures obtained. The nanoscale magnetic ferrites are of particular interest due to the unique combination of electronic and magnetic properties and their chemical compatibility with biological tissues.

Resume : Structural defects can drastically alter the electronic and other properties of 2D materials such as molybdenum disulfide (MoS2). Here, we present an atomic-level analysis of ion irradiation-induced defects in MoS2. Highly homogeneous MoS2 flakes over large areas were synthesized using the chemical vapor deposition (CVD) in a microreactor. To transfer the samples onto TEM grids, carbon coated Quantifoil TEM grids were placed onto the MoS2 flakes on silicon oxide substrates and adhered by evaporation of drops of isopropanol. The silicon dioxide layer was then etched using potassium hydroxide (KOH) to detach the TEM grid along with the MoS2 flakes. The grid was then transferred through water into isopropanol and dried. For introducing defects, the samples were irradiated by highly charged (20?40 ) Xe ions, with fluences between 2000 and 10000 ions/µm2. The atomic structure of the defects (mainly holes) was then analyzed using an aberration-corrected scanning transmission electron microscope (Nion UltraSTEM100) operated at 60 kV. The edge structure of the holes is studied at the atomic level and the number of created defects is correlated with the irradiation fluences. Similarly, the size distribution of the created holes is compared to the charge state of the ions. Due to the typical defect type (a triangular hole), MoS2 membranes exposed to ion irradiation may find applications in fields such as filtration and DNA sequencing.

Resume : 1-D quantum rod has shown extremely reduced photoluminescence (PL) intensity under the E-field, because of relatively easy carrier separation, and this phenomenon is called PL quenching and recovery (on/off characteristic). Using the on/off characteristics, quantum rods can be utilized as an emitting material for future display. CdZnS/ZnS (core/shell) structure has attracted attentions due to high PL quantum yield (PL QY) and purity of blue light (440~461 nm). So, CdZnS/ZnS structure is proper to demonstrate high quality blue emitting materials. However, this structure has problem of low on/off characteristic due to difference in valence band edge between core and shell. To solve this problem, we decided to dope ZnS with nitrogen as a p-type dopant for hole transport from core to shell. In previous reports, hole conductivity significantly increases by p-type doping. The dopant should be dispersed uniformly in the shell because doping can help transfer of hole. Therefore, we developed in-situ method which help both growth of ZnS and N doping at the same time. This method can demonstrate not only uniform doping but also optimizing peak shift. So far, we obtained peak shift (from core peak) of below 6 nm and on/off characteristic of below 70 %.

Resume : Layered transitional metal dichalcogenides (TMDs) have emerged as potential alternative channel materials for ultra-thin and low power nanoelectronics and opto-electronics devices. Highly tunable and unique electronic properties of TMDs made them promising novel materials for various other applications as well. However, in order to realize the superior performance of devices based on TMDs, the physical and chemical properties need to be understood, in particular, their defect chemistries and stabilities under various chemical environments. In order to facilitate the experimental efforts, it would be helpful to examine the atomic level insights on the properties of TMDs from first-principles calculations. In this talk, I will present our research on the defect structures, oxidation, and corresponding electronic properties of TMDs as well as its interfaces, such as MoS2/HfO2 or MoS2/MoO3. In addition, the effects of the dielectric environment on the electronic and optical properties of single layer TMDs will be discussed. Moreover, the impact of various interfacial defects on electronic properties will be included, which in fact helps to simulate the realistic interfacial phenomenon and optimize the properties of the semiconducting devices.

Resume : Thermal phase transitions, usually triggered by fluctuations caused by tuning the temperature close to a critical temperature Tc, are very familiar daily phenomena. As the temperature is lowered, thermal fluctuations decrease and eventually cease at T = 0 K. However, quantum fluctuations do not stop at 0 K. If the Tc can be brought to zero by a non-thermal parameter at a critical value, then these quantum fluctuations trigger the so-called quantum phase transitions (QPT). Certain bulk binary alloys, like PdxNi1-x [1], VxNi1-x and RhxNi1-x, are reported to possess a QPT near a critical concentration xc. In the vicinity of xc, the material shows non-conventional properties, like non-Fermi liquid behavior and quantum Griffiths phase (QGP). Further, these quantum critical phenomena are known to intricately relate with the shape of the Fermi surface. Materials at nanoscale, which have somewhat discrete nature of electron densities of states, supposedly have their Fermi surfaces different from the corresponding bulk. So, the alloys showing QPT in bulk may or may not have these transitions at nanoscale. It is, thus, quite intriguing to explore the existence of QPT in these alloy nanoparticles. In this talk, our recent results on the existence of resistivity anomaly associated with a QPT in PdxNi1-x nanoalloys [2] and the evidence of a QGP in VxNi1-x nanoalloys [3] will be presented. The on-going work on the exploration of QPT in RhxNi1-x, nanoalloys will also be discussed briefly.

Resume : Materials with stimuli responsive properties and binding affinity towards specific biomolecular entities have wide range of applications in health-care. Understanding the mechanism behind their ability to recognize (bio)molecules and their target specific spectroscopic properties can pave the way to design effective and improved molecular probes, tracers and drug molecules for the purpose of selective diagnosis of various diseases and the therapeutics[1-2]. However, the computational modeling of these materials pose enormous challenges due to their complex nature and associated larger length and time scales. It also becomes computationally very demanding since we need to explicitly describe the electronic degrees of freedom and the heterogeneous environment. Here, we discuss about some sophisticated modeling strategies based on the hybrid quantum mechanics/molecular mechanics methodlogy to model various aspects of these smart materials such as their environment specific changes in molecular geometry and electronic structure, biomacromolecular recognition and their target specific spectroscopic properties[3-8]. Referenences [1] E.D. Agdeppa, M.E. Spilker, The AAPS Journal 11(2), 286(2009). [2] W. E. Klunk, H. Engler, A. Nordberg, Y. Wang, G. Blomqvist, D. P. Holt, M. Bergstrom, et al., Annals of neurology 55, 306(2004) [3] N. Arul Murugan, J. Kongsted, Z. Rinkevicius, and H. Agren, Phys. Chem. Chem. Phys. (Comm.) 14, 1107(2012). [4] N. Arul Murugan, R. Apostolov, Z. Rinkevicius, J. Kongsted, Erik Lindahl and H. Agren, J. Am. Chem. Soc. 135(36), 13590(2013). [5] N. Arul Murugan, Magnus, J. Kongsted, Z. Rinkevicius, K. Aidas and H. Agren, J. Phys. Chem. Lett. 4, 70(2013). [6] N. Arul Murugan, J. Kongsted and H. Agren, J. Chem. Theory Comput. 9(8), 3660(2013). [7] N. Arul Murugan, R. Zalesny, J. Kongsted and H. Agren, J. Chem. Theory Comput. 10(2), 778(2014). [8] N. Arul Murugan, C. Halldin, A. Nordberg, B. Langstrom, H. Ågren, J. Phys. Chem. Lett, 2016.

Resume : Irradiation of thin films with energetic ions often leads to atomic displacements due to the ion-matter interaction,resulting in an intermixing of the film with its substrate.In the case of swift heavy ions (SHIs), the occurrence of thermal spikes via electron-phonon coupling (EPC) mediated transfer of electronic energy to lattice [1,2] has been identified as the primary cause of all observed SHI-matter interaction related phenomena.In order to estimate or predict the effect of SHI irradiation quantitatively, the EPC factor has so far been taken to be constant equal to the electron density of states (eDOS) at Fermi energy according to the free-electron theory of metals. However, in metals the electrons are under a highly non-equilibrium process and the calculation of EPC factor requires exact eDOS, which can be computed from density functional theory (DFT) [3]. Based on the above concept, we calculated composition-dependent EPC strength for a series of complete solid soluble Pd1-xNix alloys by computing their eDOSs using full-potential linearized augmented plane wave method of DFT and indeed found an x-dependence of EPC strength for the alloy system. In order to see its effect on SHI-matter interaction, we prepared these alloys on Si substrates, irradiated these with 100 MeV Au ions at 1× 10^14 ions/cm^2, and monitored the diffusions of Pd and Ni independently in Si for each case. Although the Rutherford backscattering spectra do not show any intermixing possibly due to the poor spatial resolution of the technique, the depth profiles using X-ray photoelectron spectroscopy show a considerable mixing of Pd and Ni in Pd/Si and Ni/Si systems, respectively, right after the SHI irradiation, an observation not reported earlier for these systems. Further, for an intermediate composition Pd0.23Ni0.77, the mixing efficiencies of Pd and Ni both in Si is found to be an order of magnitude less than those of pure elements. This is in complete agreement with the notion that the EPC factor must be calculated using eDOS, rather than taking as a constant, and thus supports the thermal spike model of SHI-matter interaction. References 1. Z.G. Wang, C. Dufour, E. Paumier and M. Toulemomde, J. Phys: Condensed Matter, 6 (1994) 6733 2. S.K. Srivastava,, D.K. Avasthi, W.Assmann,Z.G. Wang, H. Kucal, E. Jacquet, H.D. Carstanjen,and M. Toulemonde, Phys. Rev. B 71 (2005) 193405. 3. Z. Lin, L.V. Zhigilei, and V. Celli, Phys. Rev. B 77 (2008) 075133.

Resume : Spectroscopic properties of crystalline materials doped with the Mn4+ ions are intensively studied, both experimentally and theoretically, because of their applications for solid state lighting, holographic recording, optical data storage, dosimetry etc. These systems have been an object of our thorough investigations over several recent years [1-7 and references therein]. In the present work a particular emphasis is placed on calculations of the Mn4+ energy levels in solids by using crystal field and ab initio methods. An analysis of spectroscopic properties of Mn4+ ions allowed to establish correlation between the energy of the 2Eg?4A2g red emission transition (that is of growing importance in white LED technology) and degree of covalency of the ?Mn4+ - ligand? chemical bonds, which is determined by the degree of reduction of the Racah parameters of Mn4+ ions in solids in comparison with those for a free state. Several practical recommendations on how to tune the Mn4+ red emission are suggested. References: [1] A.M. Srivastava, M.G. Brik, J. Lumin. 132 (2012) 579. [2] M.G. Brik, A.M. Srivastava, J. Lumin. 133 (2013) 69. [3] M.G. Brik, A.M. Srivastava, Opt. Mater. 35 (2013) 1251. [4] M.G. Brik, A.M. Srivastava, ECS J. Solid State Sci. & Technol. 2 (2013) R148. [5] M.G. Brik, S.J. Camardello, A.M. Srivastava, ECS J. Solid State Sci. & Technol. 4 (2015) R39. [6] M.G. Brik, S.J. Camardello, A.M. Srivastava, N.M. Avram, A. Suchocki, ECS J. Solid State Sci. & Technol. 5 (2016) R3067. [7] M.G. Brik, A.M. Srivastava, Opt. Mater. 54 (2016) 245.

Resume : Spintronics represents a new paradigm of electronics that utilizes both the electron’s charge as well as its spin degrees of freedom. It has the potential to facilitate a new generation of devices possessing high-speed, large memory and ultra-low power consumption. The most critical step in the functioning of a spintronic device is the injection and detection of spin-polarized carriers at the ferromagnet-semiconductor interface. Despite considerable efforts, efficient injection of spins into nonmagnetic semiconductors still continues to be a major hurdle in this field. All the possible routs of injecting spin in semiconductors rely on oxides. In this talk, I will present some of our very exciting research going on in this field in my group at the University of Utah. Particular focus will be on the injection and detection of spin polarized carriers in semiconductors using electrical and thermal routes. In the later part of my talk, I will also discuss about a new oxide-based 2D material system discovered in my laboratory very recently.

Resume : The fluorescent marker Laurdan (6-lauroyl-2-(N,N-dimethylamino)naphthalene), and its new derivative, C-laurdan (6-dodecanoyl-2-[N-methyl-N-(carboxymethyl)amino]-naphtalene), have been investigated in a DOPC lipid bilayer and a comparison is made with results from fluorescence experiments. Experimentally, the latter probe is known to have a higher sensitivity to the membrane polarity at the lipid head-group region and has higher water solubility [1]. Molecular dynamics (MD) simulations are used to study the position of the fluorescent probe in the membrane, which might differ along with the membrane phase. Dependent on the temperature, the gel (S0), liquid ordered (Lo) or liquid disordered (Ld) phases are considered. Results from MD simulations show that Laurdan is oriented with the carbonyl group towards the head of the membrane, with an angle of ca. 70-80° between the molecular backbone and the normal to the bilayer, while C-laurdan presents an angle of 50°, with opposite orientation than for Laurdan. This different orientation will reflect the difference in transition dipole moment between the two probes and, in turn, the different optical properties. Preliminary QM-MM results of the probe in water show little differences in absorption spectra, while the second harmonic generation (SHG) beta component is twice as large in Laurdan with respect to C-laurdan probe. Other two probes, namely a new BODIPY-based membrane probe (BNP) [2] and DiI-C18 are described and compared. The latter one can be excited in the red spectral region, while the previous one can be pinpointed to the blue part. MD simulations of BNP in a model of the DOPC bilayer indicate that the average angle of the transition moments with respect to the membrane normal is ca. 70o, which is comparable with the value reported for DiI-C18. The affinity of both probes for different phases (Ld DOPC, DPPC in both S0 and Ld phases and Lo phase of a 2:1 mixture of Sphingomyelin and Cholesterol) are studied by Gibbs free energy profiles calculation. To investigate the influence of the different phases on the (non-) linear absorption spectra of the probes, benchmark calculations are performed using CC2 and higher order ADC methodologies. Comparison is made with TDDFT and diverse functionals. A multiscale integrated approach is further on used to assess the optical properties in both membrane and water environment, using a polarizable embedding QM/MM formalism implemented in the Dalton package of programs. One and two photon absorption spectra are investigated and the first hyperpolarizability is calculated. [1] J. Barucha-Kraszewska, S. Kraszewski, C. Ramseyer, Langmuir, 2013, 29, 1174. [2] M. Bacalum, L. N. Wang, S. Boodts, P. Yuan, V. Leen, N. Smisdom, E. Fron, S. Knippenberg, G. Fabre, P. Trouillas, D. Beljonne, W. Dehaen, N. Boens, M. Ameloot, Langmuir, 2016, 32, 3495?3505.

Resume : Five semiconductors namely ZnS, ZnO(S1), ZnO(S2), CdO and CuS have been synthesized by chemical precipitation method. After that the composites based on dispersion of the semiconductors in 4?-(hexyloxy)-4-biphenyl-carbonitrile 96% (HOBC) nematic liquid crystal have been prepared by melt-mixing method. The four composites namely ZnO(S1)/HOBC, ZnO(S2)/HOBC, CdO/HOBC and CuS/HOBC have been investigated. Confirmation of chemical structures from XRD patterns found that ZnS shows cubic zincblende structure while ZnO(S1) and ZnO(S2) exhibit hexagonal wurtzite structure. CdO belongs to face centred cubic (fcc) structure and CuS shows hexagonal structure. On examining band gap energy of semiconductors by Tauc?s plots from UV/Vis spectra, it was found that ZnO(S1) shows enhancement of band gap energy with increasing calcination temperature. The ZnO(S2) sample, which calcined at various temperatures, exhibits a peak of UV/Vis spectrum at 348 nm. The UV/Vis spectrum of CdO which calcined at 400oC shows absorption edges at 295 nm (4.2 eV) and 540 nm (2.30 eV) due to the formation of CdO during calcination (540 nm) and the partial remaining of CdS (295 nm), respectively. The thermal stabilities of semiconductors have been studied by using Thermogravimetric analysis (TGA) method. ZnO(S1) and ZnO(S2) show two decomposition steps namely the weight loss at 100-200oC and the weight loss at higher than 550oC which due to the loss of water and the decomposition of ZnO, respectively. CdO shows weight loss at about 250-450oC while CuS exhibits weight loss at about 180-300oC. Almost all composites show improvement of thermal stabilities with increasing calcination temperature. The morphology of ZnO(S2) which investigated by scanning electron microscopy (SEM) shows spherical particle of about 67-167 nm. The composites show clearing temperature (TNI), determined from DSC thermograms, at about 78.0oC which closed to that of pure HOBC matrix. In the case of ZnO(S1)/HOBC composite, addition of 5wt% ZnO shows increasing of intensity in PL spectrum in comparison to that of neat HOBC. These PL spectra of composites also show blue shift with increasing semiconductor content. Interestingly, in the case of ZnO(S2)/HOBC composite there was additional peak at 424 which due to PL of ZnO. The lowering of the peak intensity at 358 nm with increasing of ZnO(S2) content was also observed. In contrast, in the case of CdO/HOBC composite, addition of CdO content results in higher PL intensities of composites in comparison to neat HOBC matrix. There was a shift of peak toward lower energy, i.e. red shift with increasing CdO content. Finally, in the case of CuS/HOBC composite, the PL spectra of composites exhibit lowering of PL intensity with enhancement of CuS content up to 15wt%. References [1] J.S. Roy, T. Pal Majumder, R. Dabrowski, J. Mol Structure. 1098, 351-354 (2015). [2] M. Mashra, R. S. Dabrowski, R. Dhar, J. Mol Structure. 213, 247-254 (2016).

Resume : Harvesting energy from irregular/random mechanical actions in variable and uncontrollable environments is an effective approach for powering wireless mobile electronics to meet a wide range of applications in our daily life. In this work, we design and fabricate a paper-based nanogenerator (NG) utilizing piezoelectric zinc oxide nanowires (ZnO NWs) grown hydrothermally on a paper substrate. The fabricated NG is capable of harvesting ambient mechanical energy from various kinds of human motions, such as footsteps. The generated electric output from a single ZnO NWs/PVDF-TrFE NG has been used to serve as low frequency self-powered triggering sensor. Using the demonstrated piezoelectric foot-step sensor, a wireless transmission was operated successfully.

Resume : Plasmonics have been recognized as a promising platform that may premise the performance enhancement of diverse optoelectronics. Representative examples include the exploitation of plasmonic nanostructures for photovoltaic devices, photodectors, and optical biosensors. It is noted that a universal paradigm to construct high-efficiency plasmonic solar cells with long term stability has not been established. Here, we propose a few strategies to develop viable plasmonic dye-sensitized solar cells and organic photovoltaic devices based on the integration of metal-graphene oxide core-shell nanostructures or lithographically-induced plasmonic nanopatterns. The development of highly sensitive and selective photodectors has been an interesting issue yet to be resolved, for which we introduce a simple protocol for the fabrication of wavelength-selective photodiodes utilizing shape-controlled noble metal nanoparticles. Surface plasmon based optical biosensors constitute a well-established model that efficiently realized the activity of plasmonics for viable optoelectronics. We discuss plasmonic-coupling based concepts to develop optical biosensors with enhanced functions.

Resume : Water splitting under solar irradiation is a clean and renewable source for hydrogen fuel production. Major limitation for sunlight conversion relates to the band gaps of semiconducting photocatalysts (visible light excitations correspond to their widths 1.5-2.8 eV). Proper band alignment relative to both reduction (H+/H2) and oxidation (O2/H2O) potentials (4.44 eV and 5.67 eV, respectively) is required too. Doping of photocatalysts leads to appearance of induced levels in their band gaps, thus creating new optical absorption edges. It decreases energy threshold, and visible light photons become capable of overcoming the gap. Using first principles approaches within the density functional theory (DFT) based on either localized Gaussian basis functions at linear combination of atomic orbitals (LCAO) or linear augmented cylindrical waves (LACW), we perform comparative study of titania nanotubes (NTs) with fluorite morphology, which are found to be promising 1D photocatalysts for water splitting in visible light spectra. For simulations, we consider titania nanotubes with armchair (4,4) chirality, certain part of Ti atoms in which are substituted by Sc, V, Cr, Mn, Fe, Co, Ni, Cu or Zn dopants. Obtained results allow us to predict that among modified fluorite-structured TiO2 NTs Sc-doped NT are the most promising for hydrogen fuel production. Various co-doped schemes for efficient visible-light-driven water splitting using combination of 3d-metal dopants are also considered

Resume : Metal nanowires are building blocks for realizing new devices with applications in optoelectronics, spintronics, biosensing and medicine, as well as in catalysis, motors, and drug delivery[1-4]. Metal nanowires also enable fundamental studies of ballistic transport and of the effect of dimensionality on phenomena such as spin and orbital momentum and magnetic anisotropy[5,6]. However high quality, high density single crystalline materials have been surprisingly difficult to fabricate. Here we report a versatile, template-free method for fabrication of single crystalline metal and metal alloy nanowires (Co, Ni, NiCo, CoFe, and NiFe) by reduction of metal nitride precursors formed in situ by reaction of metal salts with a nitrogen source. Currently, template electrodeposition is the most commonly used method for producing uniform, high-density metal nanowires. Recent advances in the electrodeposition technique have made it possible to fabricate single crystalline nanowires from ferromagnetic, high melting temperature, metals Co, Fe and Ni and their alloys, with control over crystal structure and composition[7,8]. However the multistep technique is cumbersome and subject to surface roughening, high concentrations of stacking faults, fracturing of high aspect ratio structures, and contamination due to post-deposition template removal processes[9]. Whilst template-free self-assembly of single-crystal cobalt and nickel nanowires has been achieved, low yields and substrate limitations have limited applications of epitaxially-grown nanowires, while solvothermal growth methods typically produce aggregates of low aspect ratio nanowires[10,11]. To date, no general method of template-free self-assembly of binary or ternary metal alloy nanowires has been reported. Here we report a versatile and scalable fabrication technique for single crystalline metal and metal alloy nanowires (eg. Co, Ni, NiCo, CoFe, and NiFe)[12]. The method employs reduction of metal nitride precursors formed in situ by reaction of metal salts with a nitrogen source. Nanowires may be grown using gas-phase, solution-phase or a combination of gas- and solution-phase precursors. We also examine the roles of the reactants and intermediate metal phases in the uniaxial growth mechanism. Thiol reduction of the metal nitrides to the metallic phase at 550-600?C results in nanowire growth. In this process, sulfur acts as a uniaxial structure-directing agent, passivating the surface of the growing nanowires and preventing radial growth. The robustness and versatility of the method is demonstrated by achieving nanowire growth from gas-phase, solution-phase or a combination of gas- and solution-phase precursors. The fabrication method is suited to large-area CVD on a wide range of solid substrates. Our method will allow new generation of metallic nanowires for applications in high-performance spin based electronics, diagnostics and therapeutics. [1] H. Wu, D.S. Kong, Z.C. Ruan, P.C. Hsu, S. Wang, Z.F. Yu, T.J. Carney, L.B. Hu, S.H. Fan, Y. Cui, Nature Nanotechnology 8 (2013) 421. [2] U. Yogeswaran, S.-M. Chen, Sensors 8 (2008) 290. [3] S.A. Wolf, D.D. Awschalom, R.A. Buhrman, J.M. Daughton, S. von Molnar, M.L. Roukes, A.Y. Chtchelkanova, D.M. Treger, Science 294 (2001) 1488. [4] Y. Imura, K. Tsujimoto, C. Morita, T. Kawai, Langmuir 30 (2014) 5026. [5] F. Garcia-Sanchez, H. Szambolics, A.P. Mihai, L. Vila, A. Marty, J.P. Attane, J.C. Toussaint, L.D. Buda-Prejbeanu, Physical Review B 81 (2010) 134408. [6] R. Skomski, H. Zeng, M. Zheng, D.J. Sellmyer, Physical Review B 62 (2000) 3900. [7] H. Pan, B.H. Liu, J.B. Yi, C. Poh, S. Lim, J. Ding, Y.P. Feng, C.H.A. Huan, J.Y. Lin, J. Phys. Chem. B 109 (2005) 3094. [8] R.M. Metzger, V.V. Konovalov, M. Sun, T. Xu, G. Zangari, B. Xu, M. Benakli, W.D. Doyle, Ieee Transactions on Magnetics 36 (2000) 30. [9] G. Cao, D. Liu, Advances in Colloid and Interface Science 136 (2008) 45. [10] S.-i. Kim, H. Yoon, H. Lee, S. Lee, Y. Jo, S. Lee, J. Choo, B. Kim, Journal of Materials Chemistry C 3 (2015) 100. [11] Y. Soumare, C. Garcia, T. Maurer, G. Chaboussant, F. Ott, F. Fievet, J.Y. Piquemal, G. Viau, Adv. Funct. Mater. 19 (2009) 1971. [12] J. Scott, D. Totonjian, A. Martin, T.T. Tran, J. Fang, M. Toth, A. McDonagh, I. Aharonovich, C. Lobo, Nanoscale (2016).

Resume : Titanium dioxide (TiO2) is the cheapest with non-toxicity and higher stability. However, it suffers through poor absorption in visible irradiation due to large band gap energy of ~ 3.2 eV and high rate of recombination. To overcome these drawbacks, studies on adding doping materials or synthesizing with low band gap semiconductor materials, have been reported in the past. Hence, one of promising materials, non-metallic g-C3N4, is considered because of its band gap energy of 2.6 eV as well as its thermal and chemical stability. Moreover, the existence of g-C3N4 in visible region due to its strong covalent bonding of carbon and nitrogen atoms, has been confirmed. Additionally, it has been reported that TiO2/g-C3N4 composite showed stable state and good photoelectrochemical properties. In the present work, we tried to explore polymeric graphitic carbon nitride (g-C3N4) coating onto branched TiO2 nanorods via thermal method. Initially, aligned TiO2 nanorods were grown on to FTO (Fluorine-doped tin oxide) substrate with simple hydrothermal method at 150 °C/3h. After that, grown TiO2 film was treated with TiCl3 to make branched structures. After this, g-C3N4 layer was directly coated onto branched TiO2 structure using sintering process at 520 °C/4h in air atmosphere to increase its performance. TiO2/g-C3N4 films were analyzed via different analytical techniques to observe its improvement in absorbance and reduction in recombination losses. Based on photocatalysis measurements, it was seen that TiO2/g-C3N4 films show better performance than that of pristine. The enhanced performance was aroused form minimum recombination and strong absorbance after coating g-C3N4 onto TiO2 films. Furthermore, improvement in recombination losses were confirmed according to room temperature photoluminescence and electrochemical analysis. Finally, TiO2/g-C3N4 films showed excellent photocatalytic activities and hence could be used in water purification device technology.

Resume : This paper will present how RF-magnetron sputtering processed nanostructured thin films of metal oxides such as hematite (α-Fe2O3), titanium dioxide (TiO2) and bismuth vanadate (BiVO4) with tailored properties by hydrogen doping open up new vista of material properties, which can be transformed into advanced material technologies for solar water splitting. The effect of surface disordering by hydrogen doping in metal oxide thin films on optical, electrical and photoelectrochemical will be discussed. Herein, we demonstrate the effect of a partially reduction via hydrogen plasma treatment on metal oxide thin films as a simple and effective strategy to significantly improve the band edge positions and photoelectrochemical performance. Partially reduced hematite (Fe3O4:α-Fe2O3) by hydrogen treatment showed higher absorption cross-section under one Sun illumination and were found to be promising photoelectrode material with lower values of over-potential required to decompose water (in 1M NaOH). This was verified by substantially enhanced photocurrent densities (3.5 mA/cm2 at 1.0V/RHE) and reduced photocurrent onset potentials (from 0.87 to 0.55 V/RHE) in Fe3O4:α-Fe2O3 films, when compared to untreated hematite films. Hydrogen plasma treatment under non-equilibrium conditions did not alter the phase-structure but induced a valence dynamics among Fe-centers in the sub-surface region that was sustained by the incorporation of hydrogen in the hematite lattice.

Resume : Bi-phasic solid state composites of the type metal/metal oxide or element/element oxide can be synthesized in a single step method so called molecular "single source precursor" approach. Due to their singular genesis these nano scale composites show novel hetero-structures based on core-shell hierarchies (such as superlattices and composite nanospheres, nanorods or nanowires). They exhibit superior or new functional properties compared to their individual constituent compounds. In the current work, we review in particular the synthetical and mechanistical approach of bi-phasic (Al/Al2O3) nanostructures such as nanospheres, nanowires and nanoloops using a single source precursor. The impact of different synthetical conditions as well as of modification of surfaces by different methods including wet chemistry, vapor deposition and laser treatment and their technological relevance are presented briefly. Additionally, functional applications of the prepared surfaces are explained with some outstanding case studies. These case studies are primarily concerned with their use as biomaterials and their application in medicine as well as with their use as thin films for optics and functional surfaces. Chemical Society Reviews, 41, 2012, 5117-5130; 2. Small, 9, 2013, 1042-1046; 3. Journal of Biomedical Nanotechnology, 10, 2014, 831-845; 4. Nanotechnology, 25, 2014, 495101.

Resume : In the semiconducting oxide family, zinc oxide is a very fascinating material with an extraordinary variety of morphologies and its tetrapodal (T) shapes and other nano-micro-crystals have received considerable attention. Recently we demonstrated a novel method as strategies for ZnO:Sn nano-micro-crystals (synthesized from chemical solutions SCS) and Sn- alloyed ZnO tetrapods (grown by flame transport synthesis FTS). In the case of FTS doping and alloying with Sn metal microparticles, the formation of a second crystal phase of Zn2SnO4 was observed resulting in multiple heterojunctions which is quite promising for UV detection and gas sensing applications. On the other hand, our group developed the cost-efficient method of doped ZnO nano-micro-crystallite films synthesis by SCS at low temperatures (< 90 ºC). In this study, the UV detection performances of the ZnO:Sn nano-micro-crystallite films films and ZnO-T alloyed with Sn-oxide (ZnO-T- Zn2SnO4) were compared in order to reveal the effect of morphology, as well as the most effective type of crystal structures for fast and highly selective detection of UV light (λ = 365 nm) and gasses. The ZnO: Sn nanostructured films by SCS demonstrated a quite good UV response (≈ 125), while ZnO-T-Zn2SnO4 networks showed a higher one (≈ 609), revealing the superiority of the tetrapod networks. ZnO-T-Zn2SnO4 networks also demonstrated a much faster response time. The fabrication strategies for nanosensors based on different types of hybrid nano- and microstructured ZnO materials will demonstrated here and corresponding photoelectrical studies including device sensing performances will be discussed in detail.

Resume : Hydrogen is a renewable energy source and has many applications such as chemical production, fuel cell technology, fuel for cars, rocket engines, etc.. The detection of H2 in a wide range concentration is crucial for leak detection, safety issue and real time quantitative analysis. So, it requires hydrogen sensors that are accurate, fast and working in a wide hydrogen concentration. Various types of H2 sensors have been extensively studied depending on physico-chemical detection mechanism such as catalytic, electrochemical, resistor based, work function based, mechanical, optical and acoustic. In general, palladium (Pd) and Pd alloys are used as sensitive materials for metallic resistor type hydrogen sensor and there are several studies in literature. But there are a limited numbers of researches on hydrogen sensing properties of Pt. This work presents hydrogen (H2) sensing properties of platinum (Pt) and PtAg alloy thin films deposited on glass substrate by sputter technique with different thickness. The samples were characterized by XRD, SEM and (XPS) techniques for structural and chemical analysis. The XRD and XPS results for the Pt thin films are displayed a face-centered cubic crystalline structure. The obtained thin film contain no impurity peaks from both XRD and XPS, which is due to the high purity crystals. As the XPS spectrum of Pt from pure Pt films and PtAg films were compared, the relative shift was observed from PtAg alloy films. H2 sensing properties of Pt thin films were investigated at a temperature range from 30 °C to 200 °C. Temperature dependent resistances and the gas measurements of the Pt and PtAg alloy thin films were investigated under a dry air flow at a temperature range from 30 °C to 200 °C. The resistances of Pt thin films were linearly increased due to the their metalic structure. The H2 sensing properties of Platinum sensors were examined in the concentration range of 0.1 % - 1 % H2.It is directly proportional with temperature, and inversely proportional with the thickness of Pt thin film. The H2 gas sensing measurement results revealed that the 2 nm Pt thin film sensor is the best sensing performance to H2 at 30 °C. The sensitivity decreased at high temperatures but the best response time was obtained at high temperature with clear response-recovery, good stability. The results showed that Pt thin film sensor could be potentially used for H2 leak detection. The resistive hydrogen properties of PtAg alloy films study is going on and we will compare results from both Pt and PtAg alloys films. We think that Pt based thin film sensors and could be potentially used for H2 leak detection. This study was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) with project number of 114M853.

Resume : White LEDs with high color rendering index (CRI) are greatly demanded in general lighting applications. However, current major white LEDs composed of blue LED and yellow phosphor still have insufficient CRI, because of the lack of green and red color components. In this study, we present a new solid state phosphor material, porous SiC, which contains donor and acceptor impurities to create donor-acceptor-pair (DAP) recombination. Since this material can emit continuous visible spectrum similar to sun light, it is possible to fabricate high quality white LEDs with high CRI. Recently, we confirmed that DAP emission is enhanced and the peak wavelength is shifted to green-blue side due to the quantum size effect in porous SiC from a commercial n-type 6H-SiC substrate containing N (donor) and B (acceptor). In addition, it was reported that a non-radiative surface recombination was inhibited by specific surface passivation on porous SiC, while it has wider surface with problematic non-radiative surface recombination [1]. However, emission efficiency of such porous SiC is still low because of low B concentration of approximately 1x10^17 cm-3. In this study, we investigate an impact of doping concentrations of N and B on emission efficiency of porous SiC. As a method fabricating porous SiC, SiC samples are etched by anodic oxidation technique with a hydrofluoric acid solution. Moreover, as a passivation technique, Al2O3 deposited by atomic layer deposition (ALD) technique and annealed at a low temperature. The porous SiC after Al2O3 passivation has a broad blue-green light PL emission with a peak wavelength of 507nm, and the full width half maximum (FWHM) of 138.6nm. Compared with the porous SiC from commercial n-type substrate, the sample produced from intentionally codoped SiC has 2.63 times larger PL intensity. The result may show that the porous SiC with a combination of the bulk N and B codoped SiC is a promising candidate to generate high quality white light with a high CRI. References [1] Weifang Lu, et al. ?Photoluminescence enhancement in porous SiC passivated by atomic layer deposited Al2O3? CLEO 6-192 (2016).

Resume : Porous low-k films are used as inter metal dielectric for wiring structure in nanoelectronic devices to reduce the interconnect delay, crosstalk noise and power consumption in ULSI circuits. Present work discusses the effect of porosity on different properties of low-k films. Porous low-k nanostructures were obtained by sol-gel spin coating method. Three solutions were prepared named as Sol A, Sol B and Sol C by using tetraethyl orthosilicate as a source of Si with solvent ethanol, DI water and HF as acid catalyst in different volumetric proportions. Sol A used to obtain xerogel films while Sol B used to obtained aerogel films followed by aging in solvent and supercritical drying. In Sol C porogen was added and is removed by annealing the samples to obtain the porous low-k films. Deposition of SiO2 and incorporation of Si-F, C-C low polar bonds is confirmed from the FTIR spectra. The porous structure of low-k films were investigated by using FE-SEM and AFM characterizations. The measured porosity was observed to be 71.64%, 58.5% and 34% for silica aerogel, porogen based porous low-k and xerogel films, respectively. The calculated dielectric constant from CV measurements of fabricated MIS structures observed to be decreased from 2.2 (xerogel) to 1.73 (aerogel).

Resume : Multifunctional micro/nano devices and systems are of important applications in smart electronics for health care, human-machine interfacing, infrastructure monitoring and security. In recent years, piezophototronic effect is developed fast since it offers a new method to improve/tune the optoelectronic properties dramatically. The key characteristic of the piezo-phototronic effect is that the carrier generation, transport, separation and/or recombination at the heterojunction/interface can be tuned by modulating the piezopotential which created and further tuned by externally applied strain. Therefore, one method to enhance piezo-phototronic effect is increasing piezoelectric charge at the interface. Another method to improve piezo-phototronic effect is reducing charge carrier recombination probability, the design of semiconductor composites heterojunction/interface should take into account their band positions and band gap. By interface engineering the p-n junction, piezo-phototronic effect can be improved. Piezophototronic effect can enhance the sensitivity of photodetector dramatically. Here, we show a self-powered GaN flexible film-based metal-semiconductor-metal (MSM) UV photoswitch. The asymmetric MSM structure was designed to suppress carrier recombination and enhance carrier transport. At self-powered condition (no external bias voltage), its UV on/off ratio reaches up to 4.67*105 with high reliability of on/off switching response. Also its UV detection shows an excellent sensitivity (1.78*1012 cmHz0.5W-1). In particular, strain modulation can improve the UV on/off ratio (~154%) by piezo-phototronic effect. When combine piezophototronics effect with magnetostriction, multi-field couplings can be realized. For example, magneto-optics and electro-optics, magneto-electrics and magneto-mechanics, piezotronics and piezophototronics, which could be of interest for fabricating functional devices in the fields of energy conversion, magnetic/optical imaging, high-density optical communication and information storage, smart sensing, and so on. Besides photoelectric conversion and electroluminescence, photoluminescence can be tuned by piezoelectric charge as well. Here have developed a new method of pressure sensing by using pressure/strain induced piezoelectric charge to tune PL intensity of InGaN/GaN MQW under small strain (0~0.15 %). Such modulation effect is distinct, linear and ultrafast. Based upon it, an all optical pressure sensor array by the piezo-phototronics effect has been developed to measure dynamic pressure distribution without the need of electricity. Beyond the limitations of electrical connection, our all-optical device offers a novel and suitable way for large-area, high-uniform, high resolution, ultrahigh speed pressure/strain distribution sensing.

Resume : In this work, the photoluminescence properties of ZnO nanoparticles with various synthesis temperatures and concentrations were investigated. The photoluminescence spectra exhibit two types of emission: one is an ultraviolet UVemission centered at approximately 380 nm; and the other is a visible deep- level emission with a peak in range of 450-650 nm. The UV emission band is related to a near band-edge transition of ZnO, namely, the recombination of the free excitons , while the visible deep- level emissions band has previously been attributed to several defects in the crystal structure such as O-vacancy (VO), Zn-vacancy (VZn) , O-interstitial (Oi), Zn-interstitial (Zni), and extrinsic impurities. We show in this work that the emission energy and the intensity of the PL peaks depends remarkably not only the size but also the morphology of the elaborated nano-objects. The defects responsible for luminescence in the visible have also been identified and discussed.

Resume : Nanoscale structures from inorganic materials such as metal oxides, with complex geometries, like tetrapods, multipodes, etc. have got much more research interest because of their huge significance in technological applications. Here the potential of the recently introduced flame transport synthesis (FTS) approach will be demonstrated which offers simple and cost-effective fabrication of different types of nano- and microstructures including tetrapods from zinc oxide (ZnO) which can be freely utilized for various applications. Due to 3D spatial geometry, the ZnO tetrapods find interesting applications as advanced linkers for joining the unjoinable polymers or smart fillers to fabricate self-reporting polymer composites. If these ZnO tetrapods are agglomerated, their spatially distributed arms prohibit the close packing and this feature could be extended to build a highly porous and mechanically flexible material of macroscopic expansions in form of interconnected network. Such type of interconnected ZnO networks find lot of technological potentials, for example UV photodetection, gas sensing, and photocatalysis. These porous networks have got further scope as a sacrificial 3D templates for fabricating new class of 3D nanoarchitectured hybrid 3D materials.