Preparation of Cu2ZnSnS4 thin films by hybrid sputtering

In order to fabricate Cu₂ZnSnS₄ thin films, hybrid sputtering system with two sputter sources and two effusion cells is used. The Cu₂ZnSnS₄ films are fabricated by the sequential deposition of metal elements and annealing in S flux, varying the substrate temperature. The Cu₂ZnSnS₄ films with stoichiometric composition are obtained at the substrate temperature up to 400 °C, whereas the film composition becomes quite Zn-pool at the substrate temperature above 450 °C. The Cu₂ZnSnS₄ film shows p-type conductivity, and the optical absorption coefficient and the band gap of the Cu₂ZnSnS₄ film prepared in this experiment are suitable for fabricating a thin film solar cell.     

Role of growth temperature and oxygen partial pressure on the structural and electrical properties of pulsed laser deposited La1−xSrxnO3−δ thin films

The paper presents the fabrication and characterization of La_0.65Sr_0.35MnO_3−δ (LSMO) polycrystalline thin films deposited directly on Si (1 0 0) substrates using pulsed laser deposition technique. Various deposition parameters like substrate temperature and oxygen partial pressure have been varied systematically to obtain stoichiometric, crack-free films with smooth surface morphology having nearly monodisperse grain size distribution. The substrate temperature variation from 600 to 800 °C had profound effects on the microstructure and topography of the deposited film, with optimum result being obtained at 700 °C. The variation of partial pressure of oxygen controls the deposition kinetics as well as the stoichiometry of the film in terms of oxygen vacancy, which influences the magnetic and electrical transport properties of the manganate films. The microstructure and crystallinity of the deposited films have been studied using X-ray diffraction, scanning electron microscopy and atomic force microscopy. A correlation between the oxygen stoichiometry and micro-structural and transport properties of the deposited films has been obtained.     

Improved dielectric properties of (Pb,Ca)TiO3 thin films prepared by metal-organic decomposition method

(Pb,Ca)TiO₃ (PCT) thin films have been deposited on Pt/Ti/SiO₂/Si substrate by metal-organic decomposition (MOD) technique. The film processing parameters such as drying and annealing temperatures have been optimized to obtain good-quality PCT films. Compositional analysis of the film has been studied by X-ray photoelectron spectroscopy (XPS). The effect of the annealing temperature on the crystalline structure, microstructure and electrical properties have been investigated by X-ray diffraction, atomic force microscopy (AFM) and impedance analyzer, respectively. Amorphous PCT films form at 350 °C and crystallize in the perovskite phase following the isothermal annealing at ?650 °C for 3 h in oxygen ambient. Typical tetragonal structure of the PCT film is evidenced from X-ray diffraction pattern. The grain size in the PCT films increases with an increase in annealing temperature. Significant improvement in the dielectric constant value is observed as compared to other reported work on PCT films. The observed dielectric constant and dissipation factor at 100 kHz for 650 °C annealed PCT films are 308 and 0.015, respectively. The correlation of the film microstructural features and electrical behaviors is described.     

Morphological and optical properties of sol-gel derived 6SrO·6BaO·7Al2O3 thin films

A novel 6SrO·6BaO·7Al₂O₃ (S6B6A7) thin film deposited onto soda lime float glass via sol-gel dip coating technique is reported. The morphological and compositional properties of the S6B6A7 thin films have been investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) revealing that the films were composed of S6B6A7 nanoparticles. The optical properties of the S6B6A7 films are affected by sol concentration, film thickness and annealing temperature as revealed by UV-vis transmittance. The transparency of S6B6A7 films improved on increasing annealing temperature up to 450 °C in air. The S6B6A7 films prepared using 2, 5, and 8 (wt.%) sols and annealed at 450 °C exhibit an average transmittance of over ∼91% in wide visible range.     

Effects of substrate temperature on properties of NbNx films grown on Nb by pulsed laser deposition

NbN_x films were deposited on Nb substrate using pulsed laser deposition. The effects of substrate deposition temperature, from room temperature to 950 °C, on the preferred orientation, phase, and surface properties of NbN_x films were studied by X-ray diffraction, atomic force microscopy, and electron probe micro analyzer. We find that the substrate temperature is a critical factor in determining the phase of the NbN_x films. For a substrate temperature up to 450 °C the film showed poor crystalline quality. With temperature increase the film became textured and for a substrate temperature of 650−850 °C, mix of cubic δ-NbN and hexagonal phases (β-Nb₂N + δ′-NbN) were formed. Films with a mainly β-Nb₂N hexagonal phase were obtained at deposition temperature above 850 °C. The c/a ratio of β-Nb₂N hexagonal shows an increase with increased nitrogen content. The surface roughness of the NbN_x films increased as the temperature was raised from 450 to 850 °C.     

Planar quarter wave stacks prepared from chalcogenide Ge-Se and polymer polystyrene thin films

Planar quarter wave stacks based on amorphous chalcogenide Ge-Se alternating with polymer polystyrene (PS) thin films are reported as Bragg reflectors for near-infrared region. Chalcogenide films were prepared using a thermal evaporation (TE) while polymer films were deposited using a spin-coating technique. The film thicknesses, d∼165 nm for Ge₂₅Se₇₅ (n=2.35) and d∼250 nm for polymer film (n=1.53), were calculated to center the reflection band round 1550 nm, whose wavelengths are used in telecommunication. Optical properties of prepared multilayer stacks were determined in the range 400-2200 nm using spectral ellipsometry, optical transmission and reflection measurements. Total reflection for normal incidence of unpolarized light was observed from 1530 to 1740 nm for 8 Ge-Se+7 PS thin film stacks prepared on silicon wafer. In addition to total reflection of light with normal incidence, the omnidirectional total reflection of TE-polarized light from 8 Ge-Se+7 PS thin film stacks was observed. Reflection band maxima shifted with varying incident angles, i.e., 1420-1680 nm for 45° deflection from the normal and 1300-1630 nm for 70° deflection from the normal.     

Highly porous nickel oxide thin films prepared by a hydrothermal synthesis method for electrochromic application

We report NiO nanowall thin films prepared by a facile hydrothermal synthesis method and their electrochromic application. The as-prepared porous nanowall NiO thin films show a highly porous structure built up by many interconnected nanoflakes with a thickness of about 30 nm. The electrochromic performances of the NiO films are characterized by means of UV–vis spectroscopy and cyclic voltammetry (CV) measurements. The effect of the annealing temperature on electrochromic properties is discussed. The NiO nanowall film annealed at 300 °C exhibits much better electrochromic performance than those counterparts annealed at higher temperature. The film annealed at 300 °C exhibits a noticeable electrochromism with reversible color changes from transparent to brown dark and presents a transmittance variation with 77% at 550 nm. The NiO nanowall film also shows good reaction kinetics with fast switching speed, and the coloration and bleaching times are 3 s and 4 s, respectively. The improved electrochromic performances are due to the porous morphological characteristics with fast ion and electron transfer resulting in fast reaction kinetics and high color contrast.     

Effect of annealing temperature on the optical constants of zinc oxide films

In this paper, the effect of annealing temperature on optical constants was studied. The ZnO films were deposited on microscopic glass substrates using the sol-gel method for various annealing temperatures. The deposited zinc oxide (ZnO) films were characterized by an X-ray diffractometer (XRD), a spectrophotometer and scanning electron microscopy (SEM). The transmittance spectra recorded through the spectrophotometer exhibits 90% transmittance. The XRD spectra showed polycrystalline nature of ZnO film. Optical constants were determined through transmittance spectra using an envelope method. It was found that there was a significant effect of annealing temperature on the refractive index and extinction coefficient of deposited ZnO films. In this experiment, the optimum refractive index value of 1.97 was obtained at 350 °C annealing temperature at visible (vis) wavelength. The optical energy gap was found to be of ∼3.2 eV for all the samples. The top view of SEM showed the ZnO grain growth on the glass substrates.     

P/Si-TiO2 transparent films with high anatase stability and photocatalytic activity

The anatase-TiO₂ transparent films, containing 3 mol% of Si and P elements (as dopants), were synthesized using a process combining the sol-gel method and spin-coating technique. Effects of relative ratio of dopants and calcination temperature on phase transformation, grain growth, surface morphology, light transmittance, band-gap energy and photocatalytic activity of the P/Si-TiO₂ films were examined and their results were compared with those of the undoped-TiO₂ and Si-TiO₂ films. The P/Si-TiO₂ films calcined at temperature between 600 and 900 °C adhered strongly to the surface of fused-silica substrate and were composed of anatase-TiO₂ monophase. The photocatalytic activities of the films were measured and represented using a characteristic time constant (τ) for the methylene blue (MB) photodegradation. The small τ stands for high photocatalytic ability of the film. The P/Si-TiO₂ film, containing equalmolar Si and P dopants, calcined at 800 °C gave the best performance in photocatalysis; this film had τ=5.7 h and decomposed about 90 mole% of MB in the water after 12 h of the 365-nm UV light irradiation.     

A study on the optical and electrical properties of direct-patternable ZnO films incorporated various contents of Pt nanoparticles

Platinum nanoparticles were synthesized by the methanol reduction method, and their size was controlled to 3 nm on average using PVP [poly(N-vinyl-2-pyrrolidon)] as a protecting unit. Various contents of Pt nanoparticles were incorporated into ZnO solutions which were synthesized by a sol-gel process. ZnO films with Pt nanoparticles of various content were annealed at 500 °C and 600 °C for 1 h. The crystallinity increased with the annealing temperature and also slightly with the content of Pt nanoparticles. The sheet resistance of ZnO films decreased with the incorporation of Pt nanoparticles, however the decreasing behavior was not maintained with increasing content of Pt nanoparticles. A shift of valence band maximum energy of ZnO film with Pt nanoparticles to higher energy was also observed due to electron transfer from Pt nanoparticles to ZnO film. The optical transmittance was 88 ± 2% in the visible region for all the ZnO films. Well-defined 60 μm wide direct-patterned ZnO films containing Pt nanoparticles of 0.5 atomic percent could be formed without using dry etching process.     

Influence of temperature annealing on optical properties of SrTiO3/BaTiO3 multilayered films on indium tin oxide

We have prepared SrTiO₃/BaTiO₃ thin films with multilayered structures deposited on indium tin oxide (ITO) coated glass by a sol-gel deposition and heating at 300-650 °C. The optical properties were obtained by UV-vis spectroscopy. The films show a high transmittance (approximately 85%) in the visible region. The optical band gap of the films is tunable in the 3.64-4.19 eV range by varying the annealing temperature. An abrupt decrease towards the bulk band gap value is observed at annealing temperatures above 600 °C. The multilayered film annealed at 650 ° C exhibited the maximum refractive index of 2.09-1.91 in the 450-750 nm wavelength range. The XRD and AFM results indicate that the films annealed above 600 ° C are substantially more crystalline than the films prepared at lower temperatures which were used to change their optical band gap and complex refractive index to an extent that depended on the annealing temperature.     

Preparation of CuInGeSe4 thin films by selenization method using the Cu-In-Ge evaporated layer precursors

CuInGeSe₄ quaternary compounds are known to have a chalcopyrite-like structure and have band gaps of about 1.3 eV, suitable for optimum conversion efficiency for solar cells. We have prepared the CuInGeSe₄ thin films by the selenization method using the Cu-In-Ge evaporated layer precursors. The analyses of X-ray diffraction show that the single phase of CuInGeSe₄ is obtained by the selenization of precursors at 450-500 °C. The SEM observation of film surface shows that the grain sizes are in the order of 1-2 μm. The band gaps of selenized films close to 1.6 eV are wider than that of bulk crystals (about 1.3 eV). These films have p-type conduction and higher electrical resistivities than more 10⁵ Ω cm at room temperature.     

Effect of annealing temperature on the microstructure and optical–electrical properties of Cu–Al–O thin films

We have successfully prepared Cu–Al–O thin films on silicon (100) and quartz substrates by radio frequency (RF) magnetron sputtering method. The as-deposited Cu–Al–O film is amorphous in nature and post-annealing treatment in argon ambience results in crystallization of the films and the formation of CuAlO₂. The annealing temperature plays an important role in the surface morphology, phase constitution and preferred growth orientation of CuAlO₂ phase, thus affecting the properties of the film. The film annealed at 900 °C is mainly composed of CuAlO₂ phase and shows smooth surface morphology with well-defined grain boundaries, thus exhibiting the optimum optical–electrical properties with electrical resistivity being 79.7 Ω·cm at room temperature and optical transmittance being 80% in visible region. The direct optical band gaps of the films are found in the range of 3.3–3.8 eV depending on the annealing temperature.     

Structure and optical properties of chemically synthesized titanium oxide deposited by evaporation technique

Titanium oxide inorganic ion exchange material was synthesized by hydrolysis with water and ammonia solution. Structural feature of the synthesized titanium oxide was analyzed using X-ray diffraction, X-ray fluorescence and infrared spectrometer technique. Tentative formula of titanium oxide was determined and written as TiO₂·0.58H₂O. Titanium oxide films were deposited on glass substrates by means of an electron beam evaporation technique at room temperature from bulk sample. The films were annealed at 250, 350, 450, and 550 °C temperatures. Transmittance, reflectance, optical energy gap, refractive index and extinction coefficient were investigated. The transmittance values of 85% in the visible region and 88% in the near infrared region have been obtained for titanium oxide film annealed at 550 °C. Kubelka-Munk function was used to evaluate the absorption coefficient which was used to determine the optical band gap. It was found that the optical band gap increases with increasing annealing temperature whereas the refractive index and extinction coefficient decreases.     

Direct current magnetron sputter-deposited ZnO thin films

Zinc oxide (ZnO) is a very promising electronic material for emerging transparent large-area electronic applications including thin-film sensors, transistors and solar cells. We fabricated ZnO thin films by employing direct current (DC) magnetron sputtering deposition technique. ZnO films with different thicknesses ranging from 150 nm to 750 nm were deposited on glass substrates. The deposition pressure and the substrate temperature were varied from 12 mTorr to 25 mTorr, and from room temperature to 450 °C, respectively. The influence of the film thickness, deposition pressure and the substrate temperature on structural and optical properties of the ZnO films was investigated using atomic force microscopy (AFM) and ultraviolet-visible (UV-Vis) spectrometer. The experimental results reveal that the film thickness, deposition pressure and the substrate temperature play significant role in the structural formation and the optical properties of the deposited ZnO thin films.     

Structural and spectroscopic studies of thin film of silver nanoparticles

We report the deposition of thin film of silver (Ag) nanoparticles by wet chemical method. The as-synthesized Ag nanoparticles have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray energy dispersive spectroscopy (EDS), field emission transmission electron microscopy (FETEM) and high-resolution TEM (HRTEM), UV-vis spectroscopy and thermogravimetric-differential thermal analysis (TG-DTA) respectively. FESEM image indicates that the silver film prepared on the quartz substrate is smooth and dense. XRD pattern reveals the face-centered cubic (fcc) structure of silver nanoparticles. EDS spectrum indicates that samples are nearly stoichiometric. From TEM analysis, it is found that the size of high purity Ag nanoparticles is ranging from 10 to 20 nm with slight agglomeration. Absorption in UV-vis region by these nanoparticles is characterized by the features reported in the literature, namely, a possible Plasmon peak at ∼403 nm. Optical absorbance spectra analysis reveals that the Ag film has an indirect band structure with bandgap energy 3.88 eV. TGA/DTA studies revealed that a considerable weight loss occurs between 175 and 275 °C; and the reaction is exothermic.     

Chemical spray pyrolysis deposition and characterization of p-type CuCr1−xMgxO2 transparent oxide semiconductor thin films

A chemical spray pyrolysis technique for deposition of p-type Mg-doped CuCrO₂ transparent oxide semiconductor thin films using metaloorganic precursors is described. As-deposited films contain mixed spinel CuCr₂O₄ and delafossite CuCrO₂ structural phases. Reduction in spinel CuCr₂O₄ fraction and formation of highly crystalline films with single phase delafossite CuCrO₂ structure is realized by annealing at temperatures ?700 °C in argon. A mechanism of synthesis of CuCrO₂ films involving precursor decomposition, oxidation and reaction between constituent oxides in the spray deposition process is presented. Post-annealed CuCr_0.93Mg_0.07O₂ thin films show high (?80%) visible transmittance and sharp absorption at band gap energy with direct and indirect optical band gaps 3.11 and 2.58 eV, respectively. Lower (∼450 °C) substrate temperature formed films are amorphous and yield lower direct (2.96 eV) and indirect (2.23 eV) band gaps after crystallization. Electrical conductivity of CuCr_0.93 Mg_0.07O₂ thin films ranged 0.6-1 S cm⁻¹ and hole concentration ∼2×10¹⁹ cm⁻³ determined from Seebeck analysis. Temperature dependence of conductivity exhibit activation energies ∼0.11 eV in 300-470 K and ∼0.23 eV in ?470 K region ascribed to activated conduction and grain boundary trap assisted conduction, respectively. Heterojunction diodes of the structure Au/n-(ZnO)/p-(CuCr_0.93Mg_0.07O₂)/SnO₂ (TCO) were fabricated which show potential for transparent wide band gap junction device.     

Surface morphology and luminescence characterization of β-FeSi2 thin films prepared by pulsed laser deposition

β-FeSi₂ thin films were prepared on Si (1 1 1) substrates by pulsed laser deposition (PLD) with a sintering FeSi₂ target and an electrolytic Fe target. The thin films without micron-size droplets were prepared using the electrolytic Fe target; however, the surface without droplets was remarkably rougher using the Fe target than using the FeSi₂ target. After deposition at 600 °C and then annealing at 900 °C for 20 h, XRD indicated that the thin film prepared using the Fe target had a poly-axis-orientation, but that prepared using the FeSi₂ target had a one-axis-orientation. The PL spectra of the thin films prepared using the FeSi₂ and Fe targets at a growth temperature of 600 °C and subsequently annealed at 900 °C for 20 h had A-, B- and C-bands. Moreover, it was found that the main peak at 0.808 eV (A-band) in the PL spectrum of the thin films prepared using the FeSi₂ target was the intrinsic luminescence of β-FeSi₂ from the dependence of PL peak energy on temperature and excitation power density.     

Photoluminescence of Y2O3:Eu thin film phosphors by sol-gel deposition and rapid thermal annealing

Y₂O₃:Eu³⁺ phosphor films have been developed by using the sol-gel process. Comprehensive characterization methods such as Photoluminescent (PL) spectroscopy, X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy were used to characterize the Y₂O₃:Eu³⁺ phosphor films. In this experiment, the XRD profiles show that the Y₂O₃:Eu³⁺ phosphor films crystallization temperature and optimum annealing temperature occur at about 650 and 750 °C, respectively. The optimum dopant concentration is 12 mol% Eu³⁺ and the critical transfer distance (R_c) among Eu³⁺ ions is calculated to be about 0.84 nm. Vacuum environment is more efficient than oxygen and nitrogen to eliminate the OH content and hence yields higher luminescent phosphor films. The PL emission intensity of Y₂O₃:Eu³⁺ phosphor films is also dependent on the annealing time. It was found that the H₂O impurities were effectively eliminated after annealing time of 25 s at 750 °C in vacuum environment. From the experiment results, the schematic energy band diagram of Y₂O₃:Eu³⁺ phosphor films is constructed.     

Non-linear optical properties of silver nanoparticles prepared by hydrogen reduction method

Silver nanoparticles have been prepared using hydrogen gas as the reducing agent for silver nitrate and poly(vinyl pyrrolidone) as the capping agent; the reaction was carried out at 70 °C for 3 h. The size of the nanoparticles was found to be about 20 nm as analyzed using transmission electron micrographs. The X-ray diffraction pattern revealed the face-centered cubic (fcc) structure of silver nanoparticles. The linear absorption of Ag nanoparticles, α, is obtained about 3.71 cm⁻¹. The non-linear refractive indices of silver nanoparticles were defined by the z-scan technique using CW He-Ne laser (λ = 632.8 nm) at different incident intensities. The magnitude of non-linear refractive index (n₂) was measured to be in the order of 10⁻⁷ (cm²/W) with a negative sign. Therefore self-defocusing phenomena is taking placed for Ag nanoparticles.