Ultrasonically Sprayed Research Articles

Ultrasonically sprayed Cs3Bi2I9 thin film based self-powered photodetector

In the present work, we report lead-free, all-inorganic, Cs3Bi2I9 perovskite-inspired films developed by ultrasonic spray deposition technique at various substrate temperatures which demonstrate promising photodetection properties without any external bias or power consumption. Uniform films of excellent adhesion to the substrate deposited from 150 to 400 °C were analyzed in detail using structural, morphological, optical and electrical characterization techniques. Highly crystalline films with well-packed grains were readily obtained below 325 °C substrate temperature. In addition, the degradation of the films during the growth at higher substrate temperatures was different from the normal decomposition of Cs3Bi2I9 due to post-deposition treatments. The thin films showed direct band gaps in the range of 1.8–2.1 eV with absorption coefficients in the order of ∼104 cm−1. Photocurrent in the nanoampere range was observed in all the phase-pure films under illumination by a 50 W halogen lamp. Moreover, the thin films were chemically stable even after rapid thermal processing up to 500 °C. Furthermore, self-powered photodetection using Ag/FTO/Cs3Bi2I9/C-Ag heterostructure is demonstrated under AM1.5 radiation as well as 532 and 405 nm laser illuminations. The highest responsivity and detectivity obtained for the Cs3Bi2I9-based photodetector were 0.0051 mAW−1 and 5.93 × 108 Jones (405 nm, 50 mW), respectively. Our investigations suggest that the spray deposited Cs3Bi2I9 films are promising for self-powered devices, especially in blue light detectors.

Effects of Catalyst Composition, Loading, and Spray Parameters on the Performance of Unitized Regenerative Fuel Cell Membrane Electrode Assemblies

Proton exchange membrane unitized regenerative fuel cells (PEM-URFCs) combine the ability to both produce power (in fuel cell mode) and generate fuel and oxidant (in electrolysis mode) from the same cell. Compared with discrete fuel cell and electrolyzer systems, URFCs provide the potential for lower mass, volume, and cost. The composition and structure of the bifunctional oxygen catalyst layer (CL), which facilitates the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the same electrode, significantly affects performance and stability, particularly given the wide potential differences and different mass transport phenomena involved under operation in fuel cell or electrolysis mode. We previously showed bimetallic nanoframes provide bifunctional oxygen electrocatalysts with significantly higher activity compared with monometallic structures, evaluated using a rotating disk electrode configuration.1 Here, we investigated the effects of the oxygen CL composition, loading, and spray parameters on the performance of URFC membrane electrode assemblies (MEAs). Pt black and IrO2 catalysts were combined at different ratios and deposited at different mass loadings. Catalyst layers were sprayed directly onto membranes using an ultrasonic spray system. Within ultrasonically sprayed catalyst layers, higher spray rates resulted in improved fuel cell performance. Higher catalyst loadings improved both fuel cell and electrolyzer performance, but reached a region of diminishing returns at higher loadings. The ratio of the ORR catalyst (Pt) to the OER catalyst (IrO2) modulated the performance in both fuel cell and electrolyzer modes. Different catalyst ratios influence the catalyst utilization at higher loadings. The comparison of URFC performance at same Pt or IrO2 loadings indicates that in addition to the active catalyst itself, the non-catalytically active component influences MEA performance. This result is in line with our previous evaluation of synergistic effects of Pt and IrO2 within rotating disk electrode measurements1 and supports that in addition to the significant effects of catalyst material structure on performance, the electrode structure plays a critical role in fuel cell and electrolyzer performance in URFC MEAs. Repeated switching of URFC MEAs between fuel cell and electrolysis modes indicates that reasonable performance is maintained over the initial cycles within our single cell test configuration. References Godínez-Salomón, F.; Albiter, L.; Mendoza-Cruz, R.; Rhodes, C.P. Bimetallic Two-dimensional Nanoframes: High Activity Acidic Bifunctional Oxygen Reduction and Evolution Electrocatalysts. ACS Appl. Energy Mater. 2020, 3, 2404-2421. http://dx.doi.org/10.1021/acsaem.9b02051

Ultrasonically sprayed poly(vinylidene chloride) coating on polyurea as moisture barrier

As an emerging protective coating material, elastomeric polyurea (PU) coatings have found a variety of applications in impact resistance and anti-corrosion. However, its moisture barrier performance is not very ideal，which limits its further applications for waterproofing and anti-corrosion purposes. Improving PU's moisture barrier property is decisive in further realizing its full potential as a protective coating material. Here we provide a facile, precise, and straightforward process to improve the moisture barrier property of the PU film. The process involves coating PU film with a thin layer of poly(vinylidene chloride) (PVDC) by using ultrasonic spray coating technique. The quality of PVDC coatings was optimized through tuning of flow rate and solid content of PVDC emulsion. It was found that the thickness of PVDC coating was proportional to the number of spraying scans. Water vapor transmission rate of PVDC coated PU film was reduced by 85.11%, compared with that of pristine PU film, indicating substantial improvement of the moisture barrier property. Strong adhesion of PVDC coating on PU films was verified through cross-cut test. Aging tests of PVDC coated PU films in acid, base, salt, and heat environments verified the durability of the film, with only minor loss in the moisture barrier property and mechanical performance after aging.

Non-stoichiometric effect and disorder in as-prepared Cu2ZnSnS4 films deposited at different temperatures by ultrasonic spray pyrolysis

A better understanding of its crystal structure, the formation of possible secondary phases, defects and Cu–Zn disorder effects is needed to improve the photovoltaic device performance of CZTS films. In this direction, the effect of deposition temperature on the structural inhomogeneities, such as secondary phases and Cu–Zn disorder, etc. as well as opto-electrical properties of CZTS were experimentally examined. For this purpose, a non-stoichiometric spraying solution was prepared and ultrasonically sprayed onto glass substrates at different deposition temperatures (350 °C, 400 °C, 450 °C, and 500 °C) to obtain CZTS films. Afterward, the structural, morphological, elemental, optical, and electrical properties of the deposited films were investigated in detail. By Lorentzian deconvolution of Raman spectra, 14 Raman vibrational modes were detected and seven of these were assigned to the secondary phases. Also, the ordered-kesterite phase (337 cm−1) of CZTS was found to crystallize along with the disordered-kesterite phase (329 cm−1) due to the disorder of the cation (Cu–Zn) sublattice. Optical band gaps for CZTS films decreased from 1.89 eV to 1.42 eV with increasing in deposition temperature. It was seen that not only optical band gaps but also Cu–Zn disorder and the amount of secondary phases in CZTS films tightly depend on the deposition temperature.

Ultrasonically sprayed cobalt oxide thin films: Enhancing of some physical properties by nickel doping

In this study, the effect of Ni doping (3, 6, 9 at%) on structural, optical, electrical and magnetic properties of Co3O4 films was reported. Films were grown at 300 ± 5 °C substrate temperature via ultrasonic spray pyrolysis (USP) technique. The structural analyses showed that undoped and Ni (3%) doped films exhibit an amorphous structure. Ni doping at higher ratios caused the films to have improved crystallinity. Optical band gap values the films were found to be between 2.03 and 2.08 eV with an additional sub-band corresponding to energies varying between 1.35 and 1.46 eV. The electrical conductivity values of the films increased significantly depending on the Ni doping. The hysteresis curves of the films showed that the films have weak ferromagnetic properties. Ni doping significantly improved the structural and electrical properties of Co3O4 films making them suitable materials for technological applications.

Copper concentration effect on physical properties of ultrasonically sprayed Cu2ZnSnS4 absorber thin films for solar cell applications

Cu2ZnSnS4 (CZTS) thin films have been successfully deposited on glass substrate using ultrasonic spray pyrolysis (USP) technique with different copper concentrations ranging from 0.005 to 0.020 M. The effect of copper concentration on the structural, morphological and optoelectrical properties of deposited films has been investigated. Choice of USP method and copper concentration was found to have a crucial role in stoichiometry, band gap and conductivity of sprayed CZTS thin films. X-ray diffraction indicated that all deposited films have CZTS Kesterite structure with a preferential orientation along (112) plane confirmed by Raman scattering measurements. Copper sulfide (CuS) is present as a secondary phase in all films. The presence of this secondary phase causes films optical band broadening. Good film with nearly stoichiometric CZTS film and desirable band gap of 1.51 eV was obtained at copper concentration of 0.015 M. This result indicates that this film is suitable for being applied as an absorber layer in photovoltaic solar cells.

Studies of ultrasonically sprayed Cu2SnS3 thin films by varying Sn concentration

Cu2SnS3 (CTS) films are prepared on soda lime glass substrates by ultrasonic spray pyrolysis at different Sn concentration. The structural, composition, morphological and optical properties of the CTS films are discussed. Structural analysis confirms the formation of Cu2SnS3 tetragonal structure. Stoichiometric films are obtained with increase in Sn concentration. Films exhibited p type conductivity with energy band gap close to optimum value of 1.5 eV for thin film solar cell applications.

Phase transition of ultrasonically sprayed VOx thin films: The role of substrate temperature

In this study, vanadium oxide (VOx) semiconductor films were deposited on glass substrates using ultrasonic spray pyrolysis technique. The effect of the substrate temperature on the physical properties of the deposited thin films was investigated. For this purpose, 0.05 M VCl3 aqueous solutions were prepared and sprayed on glass substrates at different temperature of 225 °C, 275 °C, 325 °C and 375 °C. Structural properties of VOx thin films were investigated by taking x-ray diffraction (XRD) patterns and it was determined that the films deposited at 225 °C and 275 °C have tetragonal V4O9 phase while the ones deposited at 325 °C and 375 °C have mixture of α-V2O5 and β-V2O5, α-V2O5 being dominant. The optical band gap energies of the films were determined to be in the range of 2.29 eV to 2.42 eV. Electrical investigations revealed that VOx films have n-type conductivity and electrical resistivity decreased from 4.07 Ωcm to 0.67 Ωcm depending on the increase in substrate temperature. Scanning electron microscopy (SEM) images showed that morphology of the films highly is sensitive to substrate temperature.

Strontium doping effect on characteristics of ultrasonically sprayed zinc oxide thin films

In the present work, Sr-doped ZnO (SZO) thin films were grown on heated glass substrates (250 °C) by the ultrasonic spray technique. The effect of strontium concentration on the structural and physical characteristics was studied. The molar ratio of strontium in the ultrasonically sprayed solution was varied from 0 to 5 at.%. Several characterization techniques have been investigated to analyze the SZO thin films. The X-ray diffraction results showed that the SZO thin films exhibited the hexagonal wurtzite structure of ZnO with a preferential orientation along (002) plane. Scanning electron microscope indicated that the surface morphology of the SZO thin films changed with the increase in Sr concentration. No impurity was present in all the SZO films which was confirmed by the elemental composition analysis. Moreover, Fourier transform infrared spectroscopy showed the chemical bonding of zinc oxide (ZnO) and confirmed the incorporation of the dopant into the ZnO lattice. From the UV–Vis studies, it was found that the optical band gap decreased from 3.34 to 3.04 eV by increasing Sr doping concentration. Measurements of the Hall Effect indicated that all the elaborated samples exhibited n type conductivity. From all the films studied, SZO (1 at.%) was the most suitable for applications in optoelectronic devices, where a large figure of merit was required.

Membrane Electrode Assembly Fabrication Method Effects on Catalyst Layer Structure, Interfaces, and Performance

The membrane electrode assembly (MEA) is a critical component in polymer electrolyte membrane fuel cells. MEAs are often prepared by depositing the catalyst layer directly on to the membrane. In lab-scale research, catalyst coated membranes or CCMs can be prepared by hand painting or ultrasonic spraying. Catalyst-coated diffusion media (CCDM), also known as gas diffusion electrodes (GDE) have the catalyst layer deposited on the gas diffusion media. For the large-scale manufacturability of MEAs, GDEs may be easier to manufacture in a roll-to-roll (R2R) fashion because the challenges associated with membrane swelling are avoided. In addition, for R2R fabrication, there are many ink deposition methods. For example, in gravure coating, a patterned gravure roller can be used in combination with a doctor blade and a pressure roller to coat the catalyst layer. The coating quality can be optimized by modifying the rotation speed of the gravure roller.1 Alternatively, in slot die coating modification of the distance from the slot die to the substrate can be used to improve coating quality, effectively changing the sheer rate experienced by the ink. With all fabrication methods (ultrasonically sprayed, slot die R2R, micro gravure R2R, etc.) several processing parameters can be varied, impacting the structure of the electrode and its performance. Additionally, ink composition (solvent ratio, ionomer to catalyst ratio) will also have significant impact on the catalyst layer structure.2 Thus, the MEA fabrication method, the processing conditions, ink composition, and chemistry and morphology of the catalyst will all affect the surfaces and interfaces that exist in an MEA. It is important to understand these material interfaces and the structure, property, performance relationship between the catalyst layer components. Electron microscopy plays a key role in these studies. This work will highlight the importance of assessing MEAs at different scales and from different perspectives: catalyst morphology, top-down electrode view, cross-sectional MEA view. Microscopy can be a powerful tool for visualizing all the components within an electrode structure. Extraction of quantifiable parameters from digital image processing provides direct correlations with performance metrics, furthering the utility of electron microcopy for electrode studies. [1] S.A. Mauger et. al, Gravure Coating for Roll-to-Roll Manufacturing of Proton-Exchange-Membrane Fuel Cell Catalyst Layers, J. Electrochem. Soc. 165 (2018) F1012–F1018. doi:10.1149/2.0091813jes. [2] Khandavalli, S. et al. Rheological Investigation on the Microstructure of Fuel Cell Catalyst Inks. ACS Appl. Mater. Interfaces (2018). doi:10.1021/acsami.8b15039 Figure 1

Cu/SnO2 gas sensor fabricated by ultrasonic spray pyrolysis for effective detection of carbon monoxide

In this paper, we report results of morphological, structural, optical analysis of ultrasonically sprayed Cu-doped SnO2 thin films and their applications in conductometric gas sensors to detect small traces of CO molecules. Effects of Cu-doping on morphological, structural and optical properties of SnO2 nanostructures were investigated by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and UV–Vis. Spectroscopy measurements. Scanning electron microscopy revealed that porosity of the film surfaces is increased with increasing Cu-doping. From the XRD patterns, the size of the crystallites and crystal quality of the films are found to be decreased with Cu-doping. UV–Vis. spectroscopy results presented that the transmittance and bandgap can be manipulated with Cu-doping where both are decreased with Cu-doping. The relation between morphology and structure of the films with CO response properties are discussed properly. The gas response of the films with different Cu-doping has been investigated at different CO concentrations at different operating temperatures. From the sensing measurements, it is found that Cu-doping improves the SnO2 based sensor response to CO gas. Furthermore, the possible sensing mechanism to enlighten the improved gas sensing behavior of the films is proposed.

A new approach for preparation of semi-transparent superhydrophobic coatings by ultrasonic spray hydrolysis of methyltrimethoxysilane

A novel nebulizing spray hydrolysis approach was used for preparation of semi-transparent superhydrophobic coatings. Methyltrimethoxysilane was dissolved in water:ethanol mixture and ultrasonically sprayed on different substrates. Superhydrophobic coatings with a contact angle (CA) as high as 164° and a sliding angle below 5° were obtained. FESEM and AFM revealed a hierarchical micro-nano binary structure with nanometric roughness of the coatings. The coated glass substrate exhibited transmittance close to 80%. The prepared coating showed great self-cleaning and water jet repellency behaviors. The superhydrophobicity of the samples was remained after subjecting to ambient conditions for 50 days. The coating was also durable under water flushing test.

Effect of precursor type and doping concentration on the physical properties of ultrasonically sprayed aluminium and indium co-doped zinc oxide thin films

In this work, we have studied the effect of aluminium dopant precursor type and doping concentration on the structural, morphological, optical and electrical properties of Al and In co-doped zinc oxide (AIZO) thin films deposited by ultrasonic spray pyrolysis. Zinc acetate dihydrate and indium acetate were used as zinc and indium precursors, respectively. Aluminium chloride and aluminium sulphate were used as aluminium precursors. The doping concentrations of Al (1 to 3at%) and In (1 to 3at%), were varied equally and the physical properties were analyzed. X-ray diffraction examinations confirmed that AIZO films were poly crystalline and grown as a hexagonal wurtzite structure. Scanning electron microscopy observations revealed that thin films were grown with different types of hexagonal nanostructures. From the optical and electrical measurements, the figure of merit was estimated. The values were 4.09×10−3/Ω and 0.75×10−3/Ω for the AIZO thin films deposited using aluminium chloride and aluminium sulphate respectively.

Ultrasonically spray coated silver layers from designed precursor inks for flexible electronics

Integration of electronic circuit components onto flexible materials such as plastic foils, paper and textiles is a key challenge for the development of future smart applications. Therefore, conductive metal features need to be deposited on temperature sensitive substrates in a fast and straightforward way. The feasibility of these emerging (nano-) electronic technologies depends on the availability of well-designed deposition techniques and on novel functional metal inks. As ultrasonic spray coating (USSC) is one of the most promising techniques to meet the above requirements, innovative metal organic decomposition (MOD) inks are designed to deposit silver features on plastic foils. Various amine ligands were screened and their influence on the ink stability and the characteristics of the resulting metal depositions were evaluated to determine the optimal formulation. Eventually, silver layers with excellent performance in terms of conductivity (15% bulk silver conductivity), stability, morphology and adhesion could be obtained, while operating in a very low temperature window of 70 °C–120 °C. Moreover, the optimal deposition conditions were determined via an in-depth analysis of the ultrasonically sprayed silver layers. Applying these tailored MOD inks, the USSC technique enabled smooth, semi-transparent silver layers with a tunable thickness on large areas without time-consuming additional sintering steps after deposition. Therefore, this novel combination of nanoparticle-free Ag-inks and the USSC process holds promise for high throughput deposition of highly conductive silver features on heat sensitive substrates and even 3D objects.

On the role of Al in ultrasonically sprayed ZnO films

In this work, Al incorporated ZnO films have been deposited by Ultrasonic Spray Pyrolysis technique. Behavior of Al element in the structure has been tried to be clarified by investigating the structural, optical, surface and electrical properties. Compositional analysis has been performed by EDX and Al contents in the coatings have been determined as 1.1, 2.8 and 3.1 at %. X-ray diffraction patterns have shown that all films are polycrystalline with hexagonal wurtzite structure and the dominant peak is (002) ZnO for films except the one containing the highest amount of Al. Above the Al content of 2.8 at %, appearance of new phases such as Al2O3 and ZnAl2O4 in XRD patterns refers a solubility limit at this doping rate. Thicknesses and optical constants (refractive index and extinction coefficient) have been determined by spectroscopic ellipsometry technique using Cauchy-Urbach model. Al doping above the solubility limit has caused ZnO films to have lower refractive index values. Also, AFM images have shown that surface morphologies of the films lose their spherical and granular texture and transform to a randomly clustered formation with sharper upper edges above the solubility limit. Transmittance and electrical resistivity measurements have shown that Al incorporation below solubility limit (1.1 and 2.8 at %) allows maintaining the transparency together with low resistivity values. These films have value to work on and may be promising materials for optoelectronic applications.

OPTICAL PROPERTIES OF Al:ZnO THIN FILM DEPOSITED BY DIFFERENT SOL-GEL TECHNIQUES: ULTRASONIC SPRAY PYROLYSIS AND DIP-COATING

Undoped and Al-doped ZnO polycrystalline thin films have been fabricated on glass substrates by using a computer-controlled dip coating (DC) and ultrasonic spray pyrolysis (USP) systems. The film deposition parameters of DC process were optimized for the samples. In this technique, the substrate was exposed to temperature gradient using a tube furnace. In the study, the other solvent-based technique was conventional USP. The zinc salt and Al salt concentrations in the solution were kept constant as 0.1 M and 2% of Zn salt’s molarity, respectively. The optical properties were compared for the films deposited two different techniques. The optical transmission of Al:ZnO/Glass/Al:ZnO sample dip coated and the optical transmission of Al:ZnO/Glass sample ultrasonically sprayed were determined higher than 80% in the visible and near infrared region. Experimental optical transmittance spectra of the films in the forms of FilmA/Glass/FilmA and FilmA/glass were used to determine the optical constants. It was observed that the optical band gaps of Al doped ZnO films onto glass substrate were increases with increase of Al content and the absorption edge shifted to the shorter wavelength (blue shift) compared with the undoped ZnO thin film.

Structural, optical, electrical and magnetic studies of ultrasonically sprayed ZnO thin films doped with vanadium

Abstract Undoped and vanadium (V) doped (3, 6, 9 and 12 mol%) ZnO thin films were deposited onto glass substrates at the substrate temperature of 400 ± 5 °C by ultrasonic spray pyrolysis technique. Depending on the doping concentration, the variation in the structural, morphological, elemental analysis, and optical, electrical and magnetic properties were investigated by means of X-ray diffractometer (XRD), atomic force microscope (AFM) and scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS), UV–vis spectrophotometer, current-voltage (I-V) measurements and vibrating sample magnetometer (VSM), respectively. The X-ray diffraction studies have revealed that all the films were polycrystalline with hexagonal wurtzite crystal structure. The transmittance in the visible region varied between 55 and 75% and it was observed that transmittance of deposited films decreased after incorporation of vanadium. The electrical resistivity studies for all the films were carried out by using the two-probe method and it was seen that the electrical resistivity of the ZnO films decreased sharply as a consequence of V doping. The VSM measurements showed that all deposited films have intrinsic ferromagnetic behavior at room temperature and it was also found that the ferromagnetic behavior of all the films was obviously affected by doping with vanadium.

Synthesis, characterization and ellipsometric study of ultrasonically sprayed Co3O4 films

In the present study, cobalt oxide (Co3O4) films were produced using ultrasonic spray pyrolysis technique onto the glass substrate at different temperatures (200–250–300–350 °C). The effect of substrate temperature on the structural, optical, surface and electrical properties of Co3O4 films was reported. Thickness, refractive index and extinction coefficient of the films were determined by spectroscopic ellipsometry, and X-ray diffraction analyses revealed that Co3O4 films were polycrystalline fcc structure and the substrate temperature significantly improved the crystal structure of Co3O4 films. The films deposited at 350 °C substrate temperature showed the best structural quality. Transmittance, absorbance and reflectance spectra were taken by means of UV–Vis spectrophotometer, and optical band gap values were calculated using optical method. Surface images and roughness values of the films were taken by atomic force microscopy to see the effect of deposition temperature on surface properties. The resistivity of the films slightly decreases with increase in the substrate temperature from 1.08 × 104 to 1.46 × 102 Ω cm. Finally, ultrasonic spray pyrolysis technique allowed production of Co3O4 films, which are alternative metal oxide film for technological applications, at low substrate temperature.

Direct deposition of graphene nanomaterial films on polymer-coated glass by ultrasonic spraying

In this work, suspensions of two types of graphene nanomaterials — graphene nanoflowers (GNFs) and multilayer graphene (MLG) flakes — were ultrasonically sprayed into micrometer-sized droplets to directly form films on glass and methacrylic acid copolymer (MA)-modified glass substrates. Poly(vinylidene fluoride) (PVDF) was added to the suspensions to enhance the structural robustness of films. While PVDF enhanced nanomaterial binding, the MA coating boosted nanomaterial adhesion to the substrate. The films' morphology, adhesion, and electrical properties were investigated. MLG flakes produced highly irregular films, conversely GNFs formed thinner and more uniform layers. In the case of MLG flakes, films on MA-coated glass showed lower resistances compared to those on glass. GNF suspensions sprayed on MA-coated glass resulted in graphene nanostructures embedded in a predominantly dielectric polymer matrix. Thus, in the case of GNFs, films on glass exhibited lower resistances compared to those on MA-coated glass. The approach described herein can be readily extended to create films of other graphene-based materials on a variety of substrates.

Structural Properties of Ultrasonically Sprayed Al-Doped ZnO (AZO) Thin Films: Effect of ZnO Buffer Layer on AZO

Transparent aluminium-doped ZnO (AZO)-conducting oxide films were deposited on a glass substrate, using an ultrasonic spray pyrolysis (USP) system at 475°C. We investigated the effects of the Al/Zn atomic ratios on the structural properties of the AZO films. All the deposited AZO thin films presented hexagonal wurtzite structure. As Al doping increased in the film, the preferential orientation switched from [002] to [101], and crystallite sizes varied from 31.90 nm to 34.5 nm. Field emission scanning electron microscopy showed a change in the surface morphology of the AZO films with respect to the Al/Zn ratio, and secondary ion mass spectroscopy showed that the amount of Al incorporated into the films was proportional to the concentration of the starting solution. A fast Fourier transform of the AZO film measurements confirmed the presence of (100), (102), and (200) reflections, corresponding to a wurtzite structure of the AZO thin films. The plane corresponding to AZO was simulated, and matched the experimental pattern obtained from high-resolution transmission electron microscopy. An un-doped ZnO layer was deposited onto the AZO film using USP at 400°C, and a bilayer of AZO/ZnO was annealed in vacuum for 20 min at 350°C. The resistivity of these bilayer films was lower than that of a single-layered AZO film, and it further decreased by vacuum annealing.