This PDF file contains the front matter associated with SPIE Proceedings Volume 9749, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

A highly-Ga-doped ZnO (GZO) layer of thickness d grown by molecular-beam epitaxy on an undoped ZnO buffer layer exhibits enhanced mobility μ due to electron diffusion (about 2 nm) from the low-mobility GZO into the high-mobility ZnO. For d = 300 nm, the combined GZO/ZnO structure has Hall mobility μ = 34.2 cm²/V-s, due almost entirely to electrons in the GZO, whereas for d = 50, 25, or 5 nm, μ = 37.0, 43.4, and 64.1 cm²/V-s, respectively, due to the influence of electrons in the ZnO. This observation of an increase of μ with decrease in d is very unusual for thin films of GZO on various substrates. However, Poisson analysis and degenerate scattering theory accurately predict the measured values of μ vs d with no adjustable parameters. For the case d = 5 nm, only 9.7% of the electrons from the GZO diffuse into the ZnO, but those closest to the interface can have μ > 200 cm²/V-s, raising the overall mobility from 34 to 64 cm²/V-s. More complicated structures can produce higher percentages of electrons in the ZnO and thus even higher mobilities. For example, simulation shows that six repeated units of a 1-nm-GZO/2-nm-ZnO structure will have 43% of the electrons in the ZnO and an average mobility of 152 cm²/V-s. This structure has roughly the same conductance as that of a GZO-only layer having the same total thickness (18 nm), but a much lower free-carrier concentration and thus a much higher transmittance in the near IR. This “Debye-tail” technology allows optimization of the conductance/transmittance tradeoff for different applications of transparent conductive oxides.

Innovative hybrid inorganic/organic structures (HIOS) should implement exciton creation by electrical injection in inorganic semiconductors followed by resonant energy transfer and light emission from the organic semiconductor. An inherent obstacle of such designs is the typically unfavorable energy level alignment at HIOS interfaces, which assists in exciton separation thus quenching light emission. Here, we introduce a technologically relevant method to optimize the hybrid structure's energy levels: ZnO and a tailored ladder-type oligophenylene. Using an organometallic donor interlayer the ZnO work function is substantially lowered eliminating the ZnO - L4P-sp3 interfacial energy level offsets enhancing the hybrid structure's radiative emission yield sevenfold.

This work is devoted to a new family of highly emissive white phosphors for solid-state lighting (SSL) applications. The phosphors, based on yttrium aluminoborates (g-YAB) compositions, were prepared from solutions by the polymeric precursor (PP) method (modified Pechini process), involving non-toxic and low cost precursors. The resulting resins were then dried at moderate temperatures. Then, a two-step annealing treatment with controlled atmospheres (pyrolysis under nitrogen and calcination under oxygen) favored the gradual oxidation of organic moieties coming from the starting materials. This allowed avoiding the formation of impurities, which are detrimental to photoluminescence (PL) emission such as pyrolytic carbon (visible light absorber) or carbonates (PL quenchers). Thus, we have synthesized glassy yttrium aluminoborate powders exhibiting intense PL emissions extended in the whole visible range leading to warm light emissions. These PL properties arise from structural defects (non-bridging oxygen or carbon impurities such as carbonyl radicals), whose energy levels are widely extended within the large bandgap of these g-YAB powders. Moreover, these samples exhibit good thermal and chemical stabilities. We determined their internal quantum yields using near ultraviolet excitations, which reached high promising values, around 80 - 90%. This new family of lanthanide-free phosphors exhibiting intense warm white emissions, with high Color Rendering Indexes (CRI), is promising for SSL through the development of phosphor coated -LED devices.

We present a study on diopside nanotracers with persistent luminescence properties in the red-near IR range for small animal imaging. In this paper we have focused our attention on improving the persistent luminescence of diopside nanoparticles doped with transition metal and lanthanide ions. Earlier study showed that Pr³⁺ is the most suitable Ln³⁺ electron trap in Eu²⁺, Mn ²⁺ doped diopside lattice. Here, we report an optimization of both chemical composition of CaMgSi₂O₆ matrix and Eu, Mn, Pr doping elements to improve persistent luminescence. These new inorganic persistent luminescent nanoparticles (i-PLNPs) emit in the red-near infrared range for several hours and can master the difficulties due to the biological environment.

Rydberg excitons are semiconductor analogues to Rydberg atoms, where one electron is promoted to an energy level of large principal quantum number η and which behave in a manner similar to hydrogen. Their huge spatial extent results in giant dipole moments and interaction effects, which can be used to create nonlinearities at the single excitation level. In contrast to hydrogen, the effective masses and Rydberg energies involved are moderately small, so that in contrast to Rydberg atoms the high field limit of Rydberg physics can be studied using fields strengths that can be realized in the lab. Here we investigate the effects of external magnetic fields of up to 7T on Rydberg excitons both in Faraday and Voigt geometry. In both cases complicated splitting patterns emerge. We investigate the differences between the two geometries and highlight spectroscopic features that are especially easy to access using them. We show that the large number of resonances in the spectrum renders a microscopic treatment of each individual resonance implausible. We instead demonstrate general effects introduced by the field like avoided crossings and discuss alternative approaches to the level structure in terms of collective descriptions.

Strontium titanate is a complex oxide with a range of interesting properties. Annealed samples show persistent photoconductivity at room temperature. When irradiated with sub-gap light, the resistivity drops significantly. The increased conductivity persists for days with negligible decay. This unusual effect is attributed to the excitation of an electron from an acceptor defect into the conduction band. A large barrier for recapture prevents electrons from returning to the defect level. Recent work suggests that optimized annealing conditions result in weakly p-type material prior to illumination.

We investigate the optical properties and corresponding temperature-induced changes in highly uniform thin amorphous films and their bi-layer stacks grown by Atomic Layer Deposition (ALD). The environmentally driven conditions such as temperature, humidity and pressure have a significant influence on optical properties of homogeneous and heterogeneous bi-layer stacked structures of TiO₂–Al₂O₃ and subsequently affect the specific sensitive nature of optical signals from nano-optical devices. Owing to the super hydrophilic behavior and inhibited surface defects in the form of hydrogenated species, the thermo-optic coefficient (TOC) of ~ 100 nm thick ALD–TiO₂ films vary significantly with temperature, which can be used for sensing applications. On the other hand, the TOC of ~ 100 nm thick ALD–Al₂O₃ amorphous films show a differing behavior with temperature. In this work, we report on reduction of surface defects in ALD–TiO₂ films by depositing a number of ultra-thin ALD–Al₂O₃ films to act as impermeable barrier layers. The designed and fabricated heterostructures of ALD–TiO₂/Al₂O₃ films with varying ALD–Al₂O₃ thicknesses are exploited to stabilize the central resonance peak of Resonant Waveguide Gratings (RWGs) in thermal environments. The temperature-dependent optical constants of ALD–TiO₂/Al₂O₃ bi-layer films are measured by a variable angle spectroscopic ellipsometer (VASE), covering a wide spectral range 380 ≤ λ ≤ 1800 nm at a temperature range from 25 to 105 °C. The Cauchy model is used to design and retrieve refractive indices at these temperatures, measured with three angles of incidence (59°, 67°, and 75°). The optical constants of 100 nm thick ALD–TiO₂ and various combinational thicknesses of ALD–Al₂O₃ films are used to predict TOCs using a polynomial fitting algorithm.

Scanning White Light Interferometry (SWLI), now referred to as Coherence Scanning Interferometry (CSI), is established as a powerful tool for sub-nanometer surface metrology. The technique provides accurate and rapid three dimensional topographical analysis without contacting the surface under measurement. This paper will focus on recent developments of CSI using the Helical Complex Field (HCF) function that have extended its use for important thin film measurements. These developments now enable CSI to perform thin film thickness measurements, to measure the surface profile and the interfacial surface roughness of a buried interface and to derive optical constants (index of refraction _n and extinction coefficient _K).

In recent years, zinc oxide (ZnO)-based metal-oxide-semiconductor field-effect transistors (MOSFETs) have attracted much attention, because ZnO-based semiconductors possess several advantages, including large exciton binding energy, nontoxicity, biocompatibility, low material cost, and wide direct bandgap. Moreover, the ZnO-based MOSFET is one of most potential devices, due to the applications in microwave power amplifiers, logic circuits, large scale integrated circuits, and logic swing. In this study, to enhance the performances of the ZnO-based MOSFETs, the ZnObased multiple channel and multiple gate structured FinMOSFETs were fabricated using the simple laser interference photolithography method and the self-aligned photolithography method. The multiple channel structure possessed the additional sidewall depletion width control ability to improve the channel controllability, because the multiple channel sidewall portions were surrounded by the gate electrode. Furthermore, the multiple gate structure had a shorter distance between source and gate and a shorter gate length between two gates to enhance the gate operating performances. Besides, the shorter distance between source and gate could enhance the electron velocity in the channel fin structure of the multiple gate structure. In this work, ninety one channels and four gates were used in the FinMOSFETs. Consequently, the drain-source saturation current (I_DSS) and maximum transconductance (g_m) of the ZnO-based multiple channel and multiple gate structured FinFETs operated at a drain-source voltage (V_DS) of 10 V and a gate-source voltage (V_GS) of 0 V were respectively improved from 11.5 mA/mm to 13.7 mA/mm and from 4.1 mS/mm to 6.9 mS/mm in comparison with that of the conventional ZnO-based single channel and single gate MOSFETs.

We succeeded in synthesizing phosphorus (P)-doped ZnO microspheres using a ZnO sintered target containing 2 wt% of P₂O₅ by pulsed laser ablation in air. Phosphorus is one of the prospective materials for p-type ZnO. Raman peak of the Pdoped ZnO microspheres indicated local vibrational mode of P-O. Additionally, room-temperature photoluminescence (RT-PL) properties of the microsphere were investigated under laser excitation using a Q-switched Nd:YAG laser (355 nm) and He-Cd laser (325 nm) in the air. P-doped ZnO microspheres showed whispering-gallery-mode (WGM) lasing in ultraviolet (UV) region by optical pumping.

Transition metal doped-oxide semiconductor nanostructures are important to achieve enhanced and new properties for advanced applications. We describe the low temperature preparation of ZnO:Ag nanowire/nanorod (NW/NR) arrays by electrodeposition at 90 °C. The NWs have been characterized by SEM, EDX, transmittance and photoluminescence (PL) measurements. The integration of Ag in the crystal is shown. Single nanowire/nanorod of ZnO:Ag was integrated in a nanosensor structure leading to new and enhanced properties. The ultraviolet (UV) response of the nanosensor was investigated at room temperature. Experimental results indicate that ZnO:Ag (0.75 μM) nanosensor possesses faster response/recovery time and better response to UV light than those reported in literature. The sensor structure has been also shown to give a fast response for the hydrogen detection with improved performances compared to pristine ZnO NWs. ZnO:Ag nanowire/nanorod arrays electrochemically grown on p-type GaN single crystal layer is also shown to act as light emitter in LED structures. The emission wavelength is red-shifted compared to pristine ZnO NW array. At low Ag concentration a single UV-blue emission is found whereas at higher concentration of dopant the emission is broadened and extends up to the red wavelength range. Our study indicates that high quality ZnO:Ag NW/NR prepared at low temperature by electrodeposition can serve as building nanomaterials for new sensors and light emitting diodes (LEDs) structures with low-power consumption.

Detecting the UV part of the spectrum is fundamental for a wide range of applications where ZnMgO has the potential to play a central role. The shortest achievable wavelength is a function of the Mg content in the films, which in turn is dependent on the growth technique. Moreover, increasing Mg contents lead to an electrical compensation of the films, which directly affects the responsivity of the photodetectors. In addition, the metal-semiconductor interface and the presence of grain boundaries have a direct impact on the responsivity through different gain mechanisms. In this work, we review the development of ZnMgO UV Schottky photodiodes using molecular beam epitaxy and spray pyrolysis, and we analyze and compare the physical mechanisms underlying the photodetector behavior.

We report on high quality, wurtzite Mg_xZn_1-xO (MgZnO) epitaxial films grown via the PMOCVD method with a record high Mg content up to 51 %. A series of MgZnO films with various Mg content were grown on ZnO (~30 nm)/Al₂O₃(0001) and ZnO (~30 nm)/AlN (~25 nm)/Al₂O₃(0001) substrates. The band gap for the films estimated using UV-visible transmission spectroscopy ranges from 3.24 - 4.50 eV, corresponding to the fraction of Mg between _x=0.0 to _x=0.51, as determined by Rutherford backscattering spectroscopy (RBS). The cathodoluminescence (CL) measurement showed a blue shift in the spectral peak position of MgZnO, indicating an increase in Mg content. No multi-absorption edges and CL band splitting were observed, suggesting the absence of phase segregation in the as grown films. The phase purity and crystal structure of the films were further confirmed by XRD. The absence of phase separation is attributed to the fast periodic transition steps in the PMOCVD, creating a non-equilibrium system where radicals that are formed will have insufficient time to reach their energy minimum. AFM analysis of the films had decreasing surface roughness with increasing Mg content. MSM photodetector was fabricated from the films to characterize the spectral response. The devices exhibit peak response ranging between 276 - 383 nm, covering a large portion of the solar blind spectral window. Moreover, the Schottky barrier was enhanced by treating the MgZnO surface with H₂O₂, reducing the device’s dark current.

Owing to wide range bandgap tunability to more than 5 eV, the quaternary (Be,Mg)ZnO solid solutions are attractive for a variety of UV optoelectronic applications, inclusive of solar blind photodetectors, and intersubband transition devices. The mutual compensation effects of Be and Mg on the formation energy and strain allows a wide range of compositions and bandgaps beyond those achievable by MgZnO and BeZnO ternaries. Localization effects are well pronounced in such wide-bandgap semiconductor alloys due to large differences in metal covalent radii and the lattice constants of the binaries, resulting in strain-driven compositional variations within the film and consequently large potential fluctuations, in addition to that possibly caused by defects. However, carrier localization may suppress recombination through nonradiative channels, and thus, facilitate high-efficiency optoelectronic devices. To investigate potential fluctuations and localization in Be_xMg_yZn(_1-x-y)O films grown by plasma-assisted molecular beam epitaxy, optical absorption and steady-state and time-resolved photoluminescence (PL) measurements were performed. O-polar Be_xMg_yZn(_1-x-y)O samples grown on GaN templates with compositions up to x = 0.04 and y = 0.18 were used for timeresolved studies, and O-polar Be_xMg_yZn(_1-x-y)O samples grown on sapphire with compositions up to x = 0.19 and y = 0.52 were used for absorption measurements. From spectrally resolved PL transients, BeMgZnO samples with higher Mg/Be content ratio were found to exhibit smaller localization depth, Δ₀=98 meV for Be_0.04Mg_0.17Zn_0.79O and Δ₀=173 meV for Be_0.10Mg_0.25Zn_0.65O, compared to samples with smaller Mg/Be ratio, Δ₀=268 meV for Be_0.11Mg_0.15Zn_0.74O. Similar correlation is observed in temporal redshift of the PL peak position of 8 meV, 42 meV and 55 meV for Be_0.04Mg_0.17Zn_0.79O, Be_0.10Mg_0.25Zn_0.65O and Be_0.11Mg_0.15Zn_0.74O, respectively, that originates from potential fluctuations and removal of band filling effect in the localized states. PL transients indicate that emission at low temperature is dominated by recombination of localized excitons, which exhibit decay times as long as τ = 0.36 ns at the peak position. The Sshaped behavior of PL peak with change in temperature was observed for the quaternary alloy Be_0.04Mg_0.17Zn_0.79O. The degree of localization σ was determined to be 22 meV. Relatively high potential fluctuations and localization energy lead to a strong Stokes shift, which increased with bandgap reaching ~0.5 eV for O-polar BeMgZnO on sapphire with 4.6 eV absorption edge.

We report a low-voltage organic field-effect transistor consisting of an extended gate sensory area to detect various ions in a solution. The device distinguishes various ions by the shift in threshold voltage and is sensitive to multiple ions with various concentrations. X-ray photoelectron spectroscopy measurements and the resistance changes at the sensor area prove that the ions are doped into the sensitive film at the sensor area. Because of the effect of doping, the conductivity of the semiconductor polymer film changes thus causing a threshold voltage shift.

Compared to state-of-the-art modulation techniques, protonation is the most ideal to control the electrical and optical properties of transition metal oxides (TMOs) due to its intrinsic non-volatile operation. However, the protonation of TMOs is not typically utilized for solid-state devices because of imperative high-temperature annealing treatment in hydrogen source. Although one solution for room temperature (RT) protonation of TMOs is liquid-phase electrochemistry, it is unsuited for practical purposes due to liquid-leakage problem. Herein we demonstrate solid-state RT-protonation of vanadium dioxide (VO₂), which is a well-known thermochromic TMO. We fabricated the three terminal thin-film-transistor structure on an insulating VO₂ film using a water-infiltrated nanoporous glass, which serves as a solid electrolyte. For gate voltage application, water electrolysis and protonation/deprotonation of VO₂ film surface occurred, leading to reversible metal-insulator phase conversion of ~11-nm-thick VO₂ layer. The protonation was clearly accompanied by the structural change from an insulating monoclinic to a metallic tetragonal phase. Present results offer a new route for the development of electro-optically active solid-state devices with TMO materials by engineering RT protonation.

Ultrathin magnetite (Fe₃O₄) films are attractive for applications in the field of spintronics due to their ferrimagnetic behavior with assumed high degree of spin polarized electrons at the Fermi energy. For these applications, it is necessary to form epitactical bilayer structure combining ferrimagnetic magnetite with an antiferromagnetic layer. Therefore, here we study Fe₃O₄/NiO bilayers on MgO(001) substrates. Bilayers grown by reactive molecular beam epitaxy are stoichiometric and have well-developed surface and interface structures. The NiO layers are laterally pinned to the structure of the MgO(001) substrate while the magnetite films gradually relax. The interfaces show smooth morphologies and the films have very homogeneous film thickness necessary for spintronical applications. The magnetic and magneto optical properties of the Fe₃O₄/NiO bilayers were probed by the magneto optical Kerr effect. Compared to single Fe₃O₄ layers on MgO(001), the bilayers show complicated ferrimagnetic behavior depending on the azimuthal direction of the external applied field. The coercive field of the bilayers, however, is increased with the coercive field of single layer Fe₃O₄/MgO(001) structures making the Fe₃O₄/NiO bilayers attractive for spintronic applications.

Artificial neural networks have been receiving increasing attention due to their superior performance in many information processing tasks. Typically, scaling up the size of the network results in better performance and richer functionality. However, large neural networks are challenging to implement in software and customized hardware are generally required for their practical implementations. In this work, we will discuss our group’s recent efforts on the development of such custom hardware circuits, based on hybrid CMOS/memristor circuits, in particular of CMOL variety. We will start by reviewing the basics of memristive devices and of CMOL circuits. We will then discuss our recent progress towards demonstration of hybrid circuits, focusing on the experimental and theoretical results for artificial neural networks based on crossbarintegrated metal oxide memristors. We will conclude presentation with the discussion of the remaining challenges and the most pressing research needs.

Perovskite (CH₃NH₃PbI₃) solar cell (PSC) have been recently emerged as a promising cost and energy efficient light absorber material for photovoltaic applications. In this paper, we fabricated planar heterojunction (PHJ) perovskite solar cells using chemical bath deposited low temperature titanium oxide (TiO_x) compact layer as an electron collection layer. The devices modified by fullerene (C₆₀) with the thickness of 7nm show very significant improvement in photovoltaic performances compared to without modified devices leading to efficiencies as high as 9.0%. This is due to enhanced electrons more efficiently at the CH₃NH₃PbI₃ /compact-TiO_x interface from the C₆₀ leading to improved photocurrent densities and fill factors.

The Cu(In,Ga)Se₂ (CIGS) thin film solar cell technology has made a steady progress within the last decade reaching efficiency up to 22.3% on laboratory scale, thus overpassing the highest efficiency for polycrystalline silicon solar cells. High efficiency CIGS modules employ a so-called buffer layer of cadmium sulfide CdS deposited by Chemical Bath Deposition (CBD), which presence and Cd-containing waste present some environmental concerns. A second potential bottleneck for CIGS technology is its window layer made of i-ZnO/ZnO:Al, which is deposited by sputtering requiring expensive vacuum equipment. A non-vacuum deposition of transparent conductive oxide (TCO) relying on simpler equipment with lower investment costs will be more economically attractive, and could increase competitiveness of CIGS-based modules with the mainstream silicon-based technologies. In the frame of Novazolar project, we have developed a low-cost aqueous solution photo assisted electrodeposition process of the ZnO-based window layer for high efficiency CIGS-based solar cells. The window layer deposition have been first optimized on classical CdS buffer layer leading to cells with efficiencies similar to those measured with the sputtered references on the same absorber (15%). The the optimized ZnO doped layer has been adapted to cadmium free devices where the CdS is replaced by chemical bath deposited zinc oxysulfide Zn(S,O) buffer layer. The effect of different growth parameters has been studied on CBD-Zn(S,O)-plated co-evaporated Cu(In,Ga)Se₂ substrates provided by the Zentrum für Sonnenenergie-und Wasserstoff-Forschung (ZSW). This optimization of the electrodeposition of ZnO:Cl on CIGS/Zn(S,O) stacks led to record efficiency of 14%, while the reference cell with a sputtered (Zn,Mg)O/ZnO:Al window layer has an efficiency of 15.2%.

The highest and most reproducible (Cu(In,Ga)Se₂ (CIGSe) based solar-cell efficiencies are obtained by use of a very thin n-type CdS layer deposited by chemical bath deposition (CBD). However because of both Cadmium’s adverse environmental impact and the narrow bandgap of CdS (2.4–2.5 eV) one of the major objectives in the field of CIGSe technology remains the development and implementation in the production line of Cd-free buffer layers. The CBDZn( S,O) remains one the most studied buffer layer for replacing the CdS in Cu(In,Ga)Se₂-based solar cells and has already demonstrated its potential to lead to high-efficiency solar cells up to 22.3%. However one of the key issue to implement a CBD-Zn(S,O) process in a CIGSe production line is the cells stability, which depends both on the deposition conditions of CBD-Zn(S,O) and on a good band alignment between CIGSe/Zn(S,O)/windows layers. The most common window layers applied in CIGSe solar cells consist of two layers : a thin (50–100 nm) and highly resistive i-ZnO layer deposited by magnetron sputtering and a transparent conducting 300–500 nm ZnO:Al layer. In the case of CBD-Zn(S,O) buffer layer, the nature and deposition conditions of both Zn(S,O) and the undoped window layer can strongly influence the performance and stability of cells. The present contribution will be specially focused on the effect of condition growth of CBD-Zn(S,O) buffer layers and the impact of the composition and deposition conditions of the undoped window layers such as Zn_xMg_yO or Zn_xSn_yO on the stability and performance of these solar cells.

In crystalline silicon (c-Si) solar cells, carrier selective contacts are among the remaining issues to be addressed in order to reach the theoretical efficiency limit. Especially in ultra-thin-film c-Si solar cells with small volumes and higher carrier concentrations, contact recombination is more critical to the overall performance. In this paper, the advantages of using TiO_X as electron-selective layers for contact passivation in c-Si solar cells are analyzed. We characterize the metal/TiO_X/n-Si electron-selective contact with the contact recombination factor J_0c and the contact resistivity ρc for the first time. Experimental results show that both J_0c and ρc decrease after the insertion of TiO_X. In addition, the effect of post-deposition rapid-thermal-annealing (RTA) at different temperatures is also evaluated. The best J_0c of 5.5 pA/cm² and the lowest ρc of 13.6 mΩ·cm² are achieved after the RTA process. This work reveals the potential of TiO_X as an electron-selective layer for contact passivation to enable high-efficiency ultra-thin c-Si solar cells with a low cost.

Highlights from research on different nanocomposites and nanostructures for sensing and other energy related applications will be presented. The synthesized nanostructures and nanocomposites presented here were all obtained using the low temperature (< 100 °C) chemical approach. Nanostructures featured by small foot-print and synthesized by the low temperature aqueous chemical approach allows the utilization of non-conventional solid and soft substrates like e.g. glass, plastic, textile and paper. We here present results from different metal oxide nanostructures employed for chemical sensing and some innovative energy related applications. Efficient sensitive and selective sensing of dopamine, melamine, and glucose are presented as some examples of self-powered sensors utilizing the electrochemical phenomenon i.e. transferring chemical energy into electrical signal. Further the use of nanomaterials for developing selfpowered devices utilizing mechanical ambient energy is presented via piezoelectric and triboelectric effects. Here the self-powered devices and systems were relying on utilizing the electormechanical phenomenon i.e. transferring ambient mechanical energy into useful electrical energy. Finally the visibility of nanomaterials prepared by the low temperature chemical synthesis as possible low cost replacement of Pt electrodes for hydrogen production is briefly presented and discussed.

We proposed a ZnO nanorod array based optical sensor for highly sensitive refractive index (RI) detection. The sensor was fabricated by sequentially growing a seed layer and ZnO nanorod array at the endface of an optical fiber. The light coupled into the optical fiber is partially reflected at the seed layer and nanorod arry-air interface, respectively, generating an interference spectrum. When the RI of the media filled among the ZnO nanorods changes, the light path between the two reflective surfaces changes, resulting in the shift of the interference spectrum. Therefore, by monitoring the interference shift, it is able to detect the RI change. The advantages of the sensor are that 1) small size and low cost; 2) easy access to analytes and integration with micro-fluidic system; 3) easy fabrication; 4) highly sensitive. Experiments demonstrated that the proposed sensor can detect the RI change caused by exposing it to various vapor-phase analytes, leading to a potential capability of gas sensing.

We report the fabrication of thin film transistors with ZnO channel and indium molybdenum oxide electrodes by sputtering. The fabricated transistors were then exposed to glycerol. We observe a temporary change in device performance after immersion of the FET in glycerol. Control structures without channel material are also used for demonstrating that the effect of saturation current increase is not due to glycerol alone as sugar alcohol is a low conductive medium. Various electrical and optical parameters are extracted. The presented results are useful for further integration of photonics and electronics in sensing applications

The spatially resolved electrical response of polycrystalline NiO films composed of 40 nm crystallites was investigated under different relative humidity levels (RH). The topological and electrical properties (surface potential and resistance) were characterized with sub 25nm resolution using Kelvin probe force microscopy (KPFM) and conductive scanning probe microscopy under argon atmosphere at 0%, 50%, and 80% relative humidity. The dimensionality of surface features obtained through autocorrelation analysis of topological maps increased linearly with increased relative humidity, as water was adsorbed onto the film surface. Surface potential decreased from about 280mV to about 100 mV and resistance decreased from about 5 GΩ to about 3 GΩ, in a nonlinear fashion when relative humidity was increased from 0% to 80%. Spatially resolved surface potential and resistance of the NiO films was found to be heterogeneous throughout the film, with distinct domains that grew in size from about 60 nm to 175 nm at 0% and 80% RH levels, respectively. The heterogeneous character of the topological, surface potential, and resistance properties of the polycrystalline NiO film observed under dry conditions decreased with increased relative humidity, yielding nearly homogeneous surface properties at 80% RH, suggesting that the nanoscale potential and resistance properties converge with the mesoscale properties as water is adsorbed onto the NiO film.

Hybrid organic-inorganic perovskite solar cells have attracted lots of attention in recent years. Growth and properties of perovskite layer and its relationship to photovoltaic performance have been extensively studied. Comparably less attention was devoted to the research of the influence of electron transporting layer (ETL). Conventionally, TiO₂ is selected as ETL. However, photocatalytic property of this transparent conductive metal oxide reduces the stability of perovskite solar cells under illumination. To realize the commercialization, the stability of perovskite solar cell must be improved. In this study, we replace TiO₂ by In₂O₃, which is not only transparent and conductive, but also has little photocatalytic effect and it has higher electron mobility than TiO₂. Investigation on different solution process methods of In₂O₃ as ETL is demonstrated.

In this work a novel flexible acetylene (C₂H₂) gas sensor based on Ag nanoparticles decorated vertical ZnO nanorods (Ag-ZnO NRs) on PI/PTFE substrate has been investigated. The grown structure was synthesized through a simple, rapid, and low-temperature hydrothermal-RF magnetron sputtering method. The successful immobilization of Ag nanoparticles (NPs) onto the surface of ZnO nanorods contributed large effective surface area and facilitated the charge transfer process. The as-fabricated sensor exhibited enhanced C₂H₂ sensing performances at low temperature (200°C) including a broad detection range (3 - 1000 ppm), and short recovery time (39 sec). Mechanical robustness and device flexibility were investigated at different curvature angle (0 - 90°) and several times bending-relaxing process (0 – 5 × 10⁵ times). The sensor exhibited stable response magnitude with a negligible drift of ~ 2.1% for a maximum bending angle of 90o and a response drop of 8% after 5 × 10⁴ bending/relaxing processes. The superior sensing features along with outstanding flexibility to extreme bending stress indicate the sensor a promising candidate for the development of practical flexible C₂H₂ gas sensors.

Fabrication and characterizations of a flexible NO₂ sensor based on tungsten trioxide nanoparticles-loaded multi-walled carbon nanotubes-reduced graphene oxide hybrid (WO₃ NPs-loaded MWCNTs-RGO) on a polyimide/polyethylene terephthalate (PI/PET) substrate have been investigated. A viscous gel of the hybrid materials (WO₃-MWCNTs-RGO) was prepared with the assistance of α-terpineol. To observe the physical and crystalline properties of hybrid materials FESEM, TEM and XRD was carried-out. Afterwards, sensor was fabricated by drop casting hybrid solution between two fingers gold (Au) electrodes. Finally, gas sensing properties were taken out in open air environment. The sensor showed excellent sensing performance towards NO₂ including a maximum response of 17% (to 5 ppm), a limit of detection (LOD) of 1 ppm, and relatively short response/recovery time (7/15 min). The sensing behaviors of the fabricated flexible sensor were evaluated systematically at different curvature angles (0-90°) and after several times bending and relaxing (0-10⁷). The sensor exhibited excellent mechanical flexibility and sensing properties at room temperature without any significant performance degradation even at a curvature angle of 90° and after 10⁶ times bending and relaxing process. The results indicates that economical, light weight and mechanical robustness of the proposed WO₃ NPs-MWCNTs- RGO hybrid based sensor can be a promising building block for the development of high performance flexible NO₂ sensors.

We are reporting an enhancement in optical properties by changing the structure of Zn_0.85Mg_0.15O thin films through formation of crystalline hexagonal nanorods. Zn_0.85Mg_0.15O thin films were deposited on Si (100) substrate using dielectric sputter followed by annealing in oxygen ambient at temperatures of 700, 800 and 900° C for 10 seconds to reduce oxygen vacancies defects. Deposited thin film annealed at 900 °C (sample A) measured highest peak intensity and it was subjected to controlled the hydrothermal bath conditioning for forming hexagonal nanorods. Four samples were dipped in 2 different solutions with variable molar ratio of zinc nitrate hexahydrate and hexamethylentetramine for 2 and 3 hours, respectively. Samples processed in solution 1 (1:1) ratio for 2 and 3 hours were named B and C and those in solution 2 (2:1) were D and E, respectively. Photoluminescence measurement at 18K demonstrates exciton near-band-edge (NBE) emission peak at 3.61eV from Zn_0.85Mg_0.15O sample A whereas other samples exhibited slight blue shift along with bimodal peaks. The other peak observed at lower energy 3.43eV corresponds to transitions due to presence of ZnO phase in Zn_0.85Mg_0.15O. All samples compared to sample A exhibited more than 10 times increment in peak intensities with sample B producing the highest (~ 20 times). Nanorods formation was confirmed using crosssectional SEM imaging. X-ray diffraction measurements revealed that all Zn_0.85Mg_0.15O samples had (002) preferred crystal orientation with peak position at 34.7°. All nanorods samples measured lower reflectance compared to sample A, indicating high absorption in nanorods due to high scattering of light at the nanorods surface.

In this paper we report a detailed investigation of ZnO thin film properties deposited on Si<100> substrate at 400°C using RF sputtering. To reduce oxygen induced vacancies and interstitial defects in samples, variable oxygen flow rate during deposition followed by post growth annealing in oxygen ambient were carried out. Four samples were deposited under constant temperature condition but with variable oxygen partial pressure of 0%, 20%, 50% and 80% in Argon and Oxygen mixture, namely sample S1, S2 , S3 and S4 respectively. Deposited films were further annealed at 700, 800, 900 and 1000°C in oxygen ambient for 10s. Photoluminescence (PL) measurements carried at low temperature (18K) demonstrated near band edge emission peak of ZnO at 3.37eV. Increment in PL intensity was observed with increasing annealing temperature and a particular sample S4 annealed at 900 measured narrowest full width half maxima (FWHM) of ~0.1272eV. Defects peaks observed at lower energies were suppressed with increasing oxygen flow and post growth annealing, indicating improvement in film quality. From HRXRD measurement it was observed S4 sample annealed at 900°C has the highest peak intensity and narrowest FWHM compared to other samples, demonstrating the best crystalline property of annealed film at 900°C. Highest XRD peak intensity measured at 34.53° corresponds to (002) crystal orientation reveals that the films were highly caxis oriented. AFM results show increase in grain size with increasing oxygen flow and annealing temperature which ensures improvement in morphological properties of the film.

The luminescence emission of a thermographic phosphor based on trivalent chromium doped ZGO (ZnGa₂O₄) bulk as well as nanoparticles is here reported. This material has a strong temperature dependence on the optical features such as ratio of their emission bands, bandwidths, bands position as well as the lifetime decay of the Cr³⁺. This makes this material well suitable as temperature sensor. ZnGa₂O₄ (ZGO), a normal spinel, exhibits a high brightness persistent luminescence, when doped with Cr³⁺ ions and shows an emission spectrum centered at 695 nm. At the nanometric scale, ZGO is used for in vivo imaging with a better signal to background ratio than classical fluorescent NIR probes. In this work we investigate the ability of the host to be a new thermographic phosphor. Several optical features are investigated in a broad temperature range (10 K-700 K). A comparison between bulk material and nanoparticles is introduced. The obtained results could be used to determine the optimal design parameters for sensor development.