Structural and electrical properties of thin films of Pr0.8Sr0.2Fe0.8Ni0.2O3−δ

Pr_0.8Sr_0.2Fe_0.8Ni_0.2O_3−δ (PN22) films have been deposited at different temperatures on yttria-stabilized zirconia (YSZ) substrates by pulsed laser deposition (PLD) for application to thin film solid oxide fuel cell cathodes. The structure of the films was analysed by X-ray diffraction (XRD) and atomic force microscopy (AFM). A marked influence in the structural properties of the substrate temperature has been found but not of the composition. Samples deposited at temperatures below 700 °C are amorphous, with granular aspect, and with decreasing roughness with the temperature. Meanwhile, the films at 700 °C are polycrystalline and exhibit a needle-shaped surface, with the highest roughness observed. Additionally, the conducting behaviour of the films has been studied by electrochemical impedance spectroscopy (EIS) and their cathodic area specific resistance (ASR) was determined. The main part of the impedance of the testing cells is due to the electrode. The ASR values of the films of PN22 are lower than those of Pr_0.9Sr_0.1Fe_0.8Ni_0.2O_3−δ (PN12), being the lowest 0.5 Ω cm² at 850 °C for the sample PN22 deposited at room temperature.     

Synthesis and characterization of one-step electrodeposited CuIn(1−x)GaxSe2/Mo/glass films at atmospheric conditions

CuIn_(1−x)Ga_xSe₂ (CIGS) thin films were prepared by one-step electro-deposition technique from a salt bath coupled with thiocyanate complex electrolytes followed by annealing in argon atmosphere at 300 °C. The influence of deposition reduction potentials as well as the salt concentrations on the structure, morphology, composition and the optical properties were performed. A reproducible Cu-In-Ga-Se precursor layer deposition with consistent composition control was demonstrated. The as-deposited films exhibit an amorphous behavior; however the films displayed good crystallization after annealing. The films show very uniform and dense grain formation with platelet-like nanostructures. The optical properties of the films are modified due to annealing. The electrical conductivity measurements demonstrate that the transport mechanism is influenced by three different temperature regions: the ionization, extrinsic and intrinsic regions, respectively, as found in other semiconductors. However, the annealed films display downturn in conductivity at low temperature indicating that there may be trapping at localized sites or scattering of the free carriers, which may be attributed to the over growth and defect sites. The electro-deposition technique demonstrates promise of growing high-quality CIGS thin films.     

CuInxGa1−xSe2 thin films prepared by electron beam evaporation

CuIn_xGa_1−xSe₂ bulk compound of three different compositions x=0.75, 0.80 and 0.85 have been prepared using individual elements of copper, indium, gallium and selenium. Thin films of CuIn_xGa_1−xSe₂ have been deposited using the prepared bulk by electron beam evaporation method. The structural studies carried on the deposited films revealed that films annealed at 400 °C are crystalline in nature exhibiting chalcopyrite phase. The position of the (1 1 2) peak in the X-ray diffractogram corresponding to the chalcopyrite phase has been found to be dependent on the percentage of gallium in the films. The composition of the prepared bulk and thin films has been identified using energy dispersive X-ray analysis. The photoluminescence spectra of the CuIn_xGa_1−xSe₂ films exhibited sharp luminescence peaks corresponding to the band gap of the material.     

Properties of mixed-oxide MoO3/V2O5 electrochromic films coated from peroxo-polymolybdovanadate solutions

Peroxo-polymolybdovanadates with various mole ratios of Mo/V are formed by direct reaction of a mixture of metallic Mo and V with hydrogen peroxide solution. Homogeneous amorphous thin films about 0.4 μm are fabricated on an ITO glass substrate by a spin-coating technique using the peroxo-polymolybdovanadate solutions. After heat-treatment at a desired temperature (80–120°C) in air for 1 h, they show reversible electrochromism in an organic Li-electrolyte solution, and change color between greenish yellow and violet. The potential (E) versus composition (x, Li content per mole of Mo_yV_1−yO_z) diagrams for these mixed films could be approximated by two straight lines with different slopes, which suggests that in these films there are two kinds of sites with different site energies. The changes in electrochromism with heat-treatment are also discussed in relation to the micro-structure of the films.     

Enhanced electrical properties of pulsed laser-deposited CuIn0.7Ga0.3Se2 thin films via processing control

Polycrystalline CuIn_0.7Ga_0.3Se₂ thin films were prepared on soda-lime glass substrates using pulsed laser deposition (PLD) with various process parameters such as laser energy, repetition rate and substrate temperature. It was confirmed that there existed a limited laser energy, i.e. less than 300 mJ, to get phase pure CIGS thin films at room temperature. Particularly, even at room temperature, distinct crystalline CIGS phase was observed in the films. Crystallinity of the films improved with increasing substrate temperature as evidenced by the decrease of FWHM from 0.65° to 0.54°. Slightly Cu-rich surface with Cu_2−xSe phase was confirmed to exist by Raman spectra, depending on substrate temperature. Improved electrical properties, i.e., carrier concentration of ∼10¹⁸ cm⁻³ and resistivity of 10⁻¹ Ω cm at higher substrate temperature for the optimal CIGS films are assumed to be induced by the potential contributions from highly crystallized thin films, existence of Cu_2−xSe phase and diffusion of Na from substrates to films.     

(Photo)electrochemical studies on p-Sm2S3 films

p-Sm₂S₃ films were electrosynthesised from aqueous 0.05 M Sm₂O₃−0.05 M Na₂S₂O₃−0.25 M tartaric acid bath onto Ti and stainless steel coated substrates. The films were characterized using optical absorption, X-ray diffraction, optical microscopy and chemical analysis. X-ray diffraction showed that films are microcrystalline and free from elemental Sm andS. Optical absorption studies showed that the bandgap is 2.08 eV. (Photo)electrochemical studies of the films were carried out by forming a p-Sm₂S₃/KI---I₂---₂KCl/C cell configuration.The current-voltage characteristics were studied in the dark and under white light illumination and at different temperatures. The capacitance-voltage characteristics were studied at 1 kHz frequency. The type of material, junction quality factor, barrier height, flat band potential, etc., were estimated.     

Studies on photoelectrochemical (PEC) cell formed with SILAR deposited Bi2Se3–Sb2Se3 multilayer thin films

Nanocrystalline Bi₂Se₃–Sb₂Se₃ multilayer thin films were deposited by simple and less investigated successive ionic layer adsorption and reaction (SILAR) method onto glass- and fluorine-doped tin oxide (FTO)-coated glass substrate from aqueous solution. Characterizations such as XRD, surface morphology and optical absorption have been carried out for Bi₂Se₃–Sb₂Se₃ thin films onto glass substrates. The films deposited onto FTO-coated glass substrates were used to study photoelectrochemical behaviour in 0.1 M (NaOH–Na₂S–S) electrolyte and results are reported.     

Layered WO3/TiO2 nanostructures with enhanced photocurrent densities

Layered WO₃/TiO₂ nanostructures, fabricated by magnetron sputtering, demonstrate significantly enhanced photocurrent densities compared to individual TiO₂ and WO₃ layers. First, a large quantity of compositions having different microstructures and thicknesses were fabricated by a combinatorial approach: diverse WO₃ microstructures were obtained by adjusting sputtering pressures and depositing the films in form of wedges; later layers of TiO₂ nanocolumns were fabricated thereon by the oblique angle deposition. The obtained photocurrent densities of individual WO₃ and TiO₂ films show thickness and microstructure dependence. Among individual WO₃ layers, porous films exhibit increased photocurrent densities as compared to the dense layer. TiO₂ nanocolumns show length-dependent characteristics, where the photocurrent increases with increasing film thickness. However, by combining a WO₃-wedge type layer with a layer of TiO₂ nanocolumns, PEC properties strikingly improve, by about two orders of magnitude as compared to individual WO₃ layers. The highest photocurrent that is measured in the combinatorial library of porous WO₃/TiO₂ films is as high as 0.11 mA/cm². Efficient charge-separation and charge carrier transfer processes increase the photoconversion efficiency for such films.     

Structural, morphological and electrochromic properties of Nb2O5 films deposited by reactive sputtering

Nb₂O₅ films were prepared successfully by DC reactive sputtering process. The relationships among structural, morphological and electrochromic properties were studied using XRD, AFM, AES and cyclic voltammograms. Results show that the films deposited on heated substrates are composed of columnar TT-Nb₂O₅ microcrystalline with many grain-to-grain boundaries. These structural characteristics provide films strong electrochemical stability, high Li⁺ insertion/extraction reversibility and good electrochromic properties. DC reactive sputtered Nb₂O₅ films are colorless in bleached state and brownish gray in colored state and may be a promising candidate for the application in electrochromic devices.     

Preparation and electrochemical properties of Li4Ti5O12 thin film electrodes by pulsed laser deposition

Spinel Li₄Ti₅O₁₂ thin film anode material for lithium-ion batteries is prepared by pulsed laser deposition. Thin film anodes are deposited at ambient temperature, then annealed at three different temperatures under an argon gas flow and the influence of annealing temperatures on their electrochemical performances is studied. The microstructure and morphology of the films are characterized by XRD, SEM and AFM. Electrochemical properties of the films are evaluated by using galvanostatic discharge/charge tests, cyclic voltammetry and a.c. impedance spectroscopy. The results reveal that all annealed films crystallize and exhibit good cycle performance. The optimum annealing temperature is about 700 °C. The steady-state discharge capacity of the films is about 157 mAh g⁻¹ at a medium discharge/charge current density of 10 μA cm⁻². At a considerably higher discharge/charge current density of 60 μA cm⁻² (about 3.45 C) the discharge capacity of the films remains steady at a relative high value (146 mAh g⁻¹). The cycleability of the films is excellent. This implies that such films are suitable for electrodes to be used at high discharge/charge current density.     

Pyrite (FeS2) thin films prepared by spray method using FeSO4 and (NH4)2Sx

A simple spray method for the preparation of pyrite (FeS₂) thin films has been studied using FeSO₄ and (NH₄)₂S_x as precursors for Fe and S, respectively. Aqueous solutions of these precursors are sprayed alternately onto a substrate heated up to 120°C. Although Fe–S compounds including pyrite are formed on the substrate by the spraying, sulfurization of deposited films is needed to convert other phases such as FeS or marcasite into pyrite. A single-phase pyrite film is obtained after the sulfurization in a H₂S atmosphere at around 500°C for 30 min. All pyrite films prepared show p-type conduction. They have a carrier concentration (p) in the range 10¹⁶–10²⁰ cm⁻³ and a Hall mobility (μ_H) in the range 200–1 cm²/V s. The best electrical properties (p=7×10¹⁶ cm⁻³, μ_H=210 cm²/V s) for a pyrite film prepared here show the excellence of this method. The use of a lower concentration FeSO₄ solution is found to enhance grain growth of pyrite crystals and also to improve electrical properties of pyrite films.     

Electrical conductivity of CaZr0.9Y0.1O3−δ films deposited from liquid solutions

CaZr_0.9Y_0.1O_3−δ (CZY) films were fabricated by chemical solution deposition (CSD) from ethanol-based liquid solutions. The films were deposited on single crystals of yttria-stabilized zirconia (YSZ) in (100), (110) and (111) crystallographic orientations. The structural, mechanical and electrical properties of the films have been studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and nanoindentation and impedance spectroscopy methods. XRD and SEM results have shown that the films were polycrystalline. Effect of the substrate orientation on the microstructural, mechanical and electrical properties of CZY films has been examined. The films deposited on (110)-substrates consist of the largest grains; show the highest values of hardness and electrical conductivity. Conductivity of CZY film on (110)-substrates increases with rise in humidity which proves proton transport in the films.     

V0.50Ti0.50Ox thin films as counterelectrodes for electrochromic devices

Thin films of V_0.50Ti_0.50O_x have been deposited by RF sputtering from metallic targets. Their use as potential counterelectrodes in electrochromic devices has been investigated. It is found that although they are slightly yellow looking in transmission, the films can reversibly store relatively large amounts of charge, whilst showing a reasonably low electrochromic colouration efficiency. The electrochemistry of V_0.50Ti_0.50O_x is found to be simple, in fact rather similar to that of WO₃, making it an almost ideal material to use in such a variable transmission device.     

Pre-existence of HxWO3 in e-beam deposited WO3 films

Structural and optical properties of e-beam deposited tungsten trioxide (WO₃) films in as-deposited and electrochemically coloured states were investigated by spectrophotometric and XRD techniques. These investigations have shown the as-deposited WO₃ films to be porous and with small amount of H_xWO₃ pre-existing in them. The films further facilitate insertion of H⁺ ions on colouration resulting in tetragonal H_xWO₃ with a = 4.74Å and c = 3.19Å.     

Electrochromic behaviour of Nb2O5 thin films with different morphologies obtained by spray pyrolysis

Two different procedures to stabilize the precursor NbCl₅ have been applied to obtain Nb₂O₅ thin films by spray pyrolysis. Depending on the procedure used, determined by the way in which the precursor solution was injected into the air stream of the spray nozzle, niobium oxide thin films with different surface morphologies can be obtained. The structural properties of the Nb₂O₅ thin films depend on the post-annealing temperature because as-deposited films are amorphous, independently of the synthesis procedure used. The electrochromic behaviour has been estimated for all films, where monochromatic colouration efficiency (at 660 nm) of 25.5 cm²/C and a cathodic charge density close to 24 mC/cm² were found to give the best results to date for niobium oxide thin films obtained by spray pyrolysis.     

Color change of V2O5 thin films upon exposure to organic vapors

The reaction of amorphous V₂O₅ thin films with various organic vapors is investigated using in-situ optical transmission and in-situ Raman spectroscopic measurements. When V₂O₅ thin films are exposed to vapors of methanol, ethanol, acetone, and isopropanol, changes in the Raman spectrum are observed. These changes are similar to those due to alkali ion intercalation and most pronounced for methanol and ethanol. The optical transmission also increases when the thin films are exposed to methanol and ethanol vapors. Depositing a thin catalyst layer of palladium does not promote the reaction. This result has implications for using this material in hydrogen sensor applications, as extended exposure to organic vapors may not be differentiated from the presence of hydrogen.     

p-Type CuSbS2 thin films by thermal diffusion of copper into Sb2S3

We report the preparation of copper antimony sulfide (CuSbS₂) thin films by heating Sb₂S₃/Cu multilayer in vacuum. Sb₂S₃ thin film was prepared from a chemical bath containing SbCl₃ and Na₂S₂O₃ salts at room temperature (27 °C) on well cleaned glass substrates. A copper thin film was deposited on Sb₂S₃ film by thermal evaporation and Sb₂S₃/Cu layers were subjected to annealing at different conditions. Structure, morphology, optical and electrical properties of the thin films formed by varying Cu layer thickness and heating conditions were analyzed using different characterization techniques. XRD analysis showed that the thin films formed at 300 and 380 °C consist of CuSbS₂ with chalcostibite structure. These thin films showed p-type conductivity and the conductivity value increased with increase in copper content. The optical band gap of CuSbS₂ was evaluated as nearly 1.5 eV.     

TiO2 and TiO2–SiO2 thin films and powders by one-step soft-solution method: Synthesis and characterizations

Simple soft-solution method has been developed to synthesize films and powders of TiO₂ and mixed TiO₂–SiO₂ at relatively low temperatures. This method is simple and inexpensive. Furthermore, reactor can be designed for large-scale applications as well as to produce large quantities of composite powders in a single step. For the preparation of TiO₂, we used aqueous acidic medium containing TiOSO₄ and H₂O₂, which results in a peroxo-titanium precursor while colloidal SiO₂ has been added to the precursor for the formation of TiO₂–SiO₂. Post annealing at 500 °C is necessary to have anatase structure. Resulting films and powders were characterized by different techniques. TiO₂ (anatase) phase with (1 0 1) preferred orientation has been obtained. Also in TiO₂–SiO₂ mixed films and powders, TiO₂ (anatase) phase was found. Fourier transform infrared spectroscopy (FTIR) results for TiO₂ and mixed TiO₂–SiO₂ films have been presented and discussed. The method developed in this paper allowed obtaining compact and homogeneous TiO₂ films. These compact films are highly photoactive when TiO₂ is used as photo anode in an photoelectrochemical cell. Nanoporous morphology is obtained when SiO₂ colloids are added into the solution.     

Spray pyrolysis of CuInS2

Spray pyrolysis is a low-cost method of depositing thin films and is economically more attractive than other methods that have been used to produce stable CuInS₂ thin films. The electrical, optical and structural properties of the films, as prepared, are presented together with their evolution and with a variation of some fabrication parameters which are the fabrication temperature T_S, and the ionic ratio R = Cu : In : S in the solution.     

Formation and metal-to-insulator transition properties of VO2-ZrV2O7 composite films by polymer-assisted deposition

VO₂-ZrV₂O₇ composite films were prepared on silica glass substrates by polymer-assisted deposition using a V-Zr-O solution. The coexistence of ZrV₂O₇ and VO₂ was confirmed by Raman spectroscopy, glance angle X-ray diffraction, and X-ray photoelectron spectroscopy. The composite films with similar thickness of about 95 nm showed decreased particle sizes and significantly enhanced luminous transmittances (from 32.3% at Zr/V=0 to 53.4% at Zr/V=0.12) with increasing Zr/V rations. The enhancement in the luminous transmittance was ascribed to the absorption-edge changes in the composite films. This feature benefits the application of VO₂ to smart windows.