Electrochemical deposition and characterization of cupric oxide thin films

Polycrystalline cupric oxide (CuO) thin films are deposited using an alkaline solution bath employing cathodic electrodeposition method. Thin films are electroplated at various bath temperatures onto conducting indium tin oxide coated glass substrates. The bath temperature effects on the structural, optical and morphological properties of copper oxide films are studied and reported. X-ray diffraction studies revealed mixed phases of monoclinic and cubic for films grown at lower bath temperatures and that the deposited films at temperatures optimized as 75 °C exhibited cubic structure with preferential orientation along a (111) plane. Texture coefficient (T_c) values are calculated for all diffraction lines and the films were highly textured (T_c > 1). The surface morphology and surface roughness are estimated using scanning electron microscopy and atomic force microscopy, respectively and a morphology made up of pyramid shaped grains is presented. Energy dispersive analysis by X-rays revealed that the near stoichiometric CuO thin films are obtained at optimized preparative parameters. The refractive index is calculated using the envelop method. Also, the optical constants of CuO thin films such as complex dielectric constant (ε) and extinction coefficient (k) are also evaluated and reported.     

Characterization of electroplated FeSe thin films

Thin films of iron selenide (FeSe) were electrodeposited on tin oxide coated conducting glass substrates at various bath temperatures, deposition potential and solution pH values. The deposited films were characterized by X-ray diffraction, energy dispersive X-ray analysis, scanning electron microscopy and optical absorption techniques, respectively. The structure was found to be hexagonal with preferential orientation along {002} plane. X-ray line profile analysis technique by the method of variance has been used to evaluate the microstructural parameters. The variation of microstructural parameters with bath temperature, deposition potential and solution pH values were studied. The observed results are discussed in detail.     

Room temperature deposition of ZnSe thin films by successive ionic layer adsorption and reaction (SILAR) method

The zinc selenide (ZnSe) thin films are deposited onto glass substrate using relatively simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. The films are deposited using zinc acetate sodium selenosulphate precursors. The concentration, pH, immersion and rinsing times and number of immersion cycles have been optimized to obtain good quality ZnSe thin films. The X-ray diffraction (XRD) study and scanning electron microscopy (SEM) studies reveals nanocrystalline nature alongwith some amorphous phase present in ZnSe thin films. Energy dispersive X-ray (EDAX) analysis shows that the films are Se deficient. From optical absorption data, the optical band gap ‘E_g’ for as-deposited thin film was found to be 2.8 eV and electrical resistivity in the order of 10⁷ Ω cm.     

Growth of crystalline HgCr2S4 thin films at mild reaction conditions

Thin films of crystalline HgCr₂S₄ have been deposited on glass substrates at low temperature as low as 65 °C using a chemical bath deposition method. Typical thickness of the deposited HgCr₂S₄ thin films was 264 nm.The films were composed of closely packed irregular grains of 165-175 nm in diameter. The X-ray diffraction analysis and the selected area electron diffraction analysis revealed the deposited thin films were polycrystalline with highly (2 2 0) preferential orientation. The films exhibit a pure faint black. Their direct band gap energy was 2.39 eV with room temperature electrical resistivity of the order of 10⁻³ Ω cm.     

Hydrophilic properties of nano-TiO2 thin films deposited by RF magnetron sputtering

Microstructure and hydrophilicity of nano-titanium dioxide (TiO₂) thin films, deposited by radio frequency magnetron sputtering, annealed at different temperatures, were studied by field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and water contact angle methods. It is found that the crystal phase transforms from amorphous to rutile structure with increase of annealing temperature from room temperature to 800 °C. It is also indicated that the organic contaminants on the surface of the films can be removed and the oxygen vacancies can be reduced by the annealing treatment. Annealed at the temperature below 300 °C, amorphous TiO₂ thin films show rather poor hydrophilicity, and annealed at the temperature range from 400 to 650 °C, the super hydrophilicity anatase of TiO₂ thin films can be observed. However, when the annealing temperature reaches 800 °C, the hydrophilicity of the films declines mainly derived from the appearance of rutile.     

Development of smooth CuInGa precursor films for CuIn1 − xGaxSe2 thin film solar cell applications

CuInGa precursor thin films were deposited using a CuGa (75-25 at.%) and an In 3″ diameter target material simultaneously by RF magnetron sputtering. The precursor films were deposited on Si and glass substrates at − 80 °C and room temperature, and characterized by Rutherford backscattering spectroscopy, Auger electron spectroscopy, scanning electron microscopy, atomic force microscopy and X-ray diffraction. The effects of gun power density and substrate temperatures on resulting precursor film properties were investigated. Precursor films deposited at − 80 °C have a smooth morphology with a 75% reduction in all roughness values and are more dense and homogeneous in structure compared to precursors deposited at room temperature. Therefore these precursors will result in better selenization process reproducibility.     

Preparation of anatase TiO2 thin films for dye-sensitized solar cells by DC reactive magnetron sputtering technique

Anatase titanium dioxide (TiO₂) thin films are prepared by DC reactive magnetron sputtering using Ti target as the source material. In this work argon and oxygen are used as sputtering and reactive gas respectively. DC power is used at 100 W per 1 h. The distance between the target and substrate is fixed at 4 cm. The glass substrate temperature value varies from room temperature to 400 °C. The crystalline structure of the films is determined by X-ray diffraction analysis. All the films deposited at temperatures lower than 300 °C were amorphous, whereas films obtained at higher temperature grew in crystalline anatase phase. Phase transition from amorphous to anatase is observed at 400 °C annealing temperature. Transmittances of the TiO₂ thin films were measured using UV-visible NIR spectrophotometer. The direct and indirect optical band gap for room temperature and substrate temperature at 400 °C is found to be 3.50, 3.41 eV and 3.50, 3.54 eV respectively. The transmittance of TiO₂ thin films is noted higher than 75%. A comparison among all the films obtained at room temperature showed a transmittance value higher for films obtained at substrate temperature of 400 °C. The morphology of the films and the identification of the surface chemical stoichiometry of the deposited film at 400 °C were studied respectively, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The surface roughness and the grain size are measured using AFM.     

Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition

We report on the self-limiting growth and characterization of aluminum nitride (AlN) thin films. AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH₃). At 185 °C, deposition rate saturated for TMA and NH₃ doses starting from 0.05 and 40 s, respectively. Saturative surface reactions between TMA and NH₃ resulted in a constant growth rate of ~ 0.86 Å/cycle from 100 to 200 °C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (≥ 225 °C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185 °C were investigated by X-ray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, respectively. Films deposited at 185 °C were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction. High-resolution transmission electron microscopy images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at ~ 5.8 eV and an optical transmittance of > 95% in the visible region of the spectrum.     

Synthesis of nanocrystalline iron oxide ultrathin films by thermal decomposition of iron nitropruside: Structural and optical properties

Ultrathin films of nanocrystalline α-Fe₂O₃ have been deposited on glass substrates from an inorganic precursor, iron nitropruside. This is a novel route of synthesis for iron oxide thin films on glass substrates, by annealing the precursor thin film in air at 650 °C for 15 min. The films were characterized using TG-DTA analysis, X-ray diffraction, UV-visible, FESEM, AFM and Raman measurements. X-ray diffraction and Raman analyses revealed that the deposited films contain α-phase of Fe₂O₃ (hematite). The synthetic route described here provides a very simple and cost-effective method to deposit α-Fe₂O₃ thin films on glass substrates with band gap energy of about 2.75 eV. The deposited films were found to show catalytic effect for the photo-degradation of phenol.     

Low-temperature fabrication of superconducting FeSe thin films by pulsed laser deposition

Superconducting FeSe thin films were prepared at a substrate temperature of 320 °C by pulsed laser deposition. X-ray diffraction and transmission electron microscopic analyses showed that highly c-axis-orientated and high-quality films were obtained on various substrate materials, including single-crystal MgO, LaAlO₃, SrTiO₃ and (100)-Si, and amorphous-SiO_x, at such low temperature. From transport measurements all the films showed low-temperature structural phase transition at ∼ 60-90 K and superconducting transition at onset temperature varies from ∼ 7 K to < 2 K, depending on the substrate used. The transport property of FeSe film on Si was found most different from all the others, in spite of their similarity in structural analysis. Chemical analysis demonstrated that Fe and Se homogeneously distributed in the film and the stoichiometry of FeSe and the bonding states of Fe and Se are as well uniform along the film growth direction.     

Spray pyrolysis deposition of indium sulphide thin films

In₂S₃ thin films were grown by the chemical spray pyrolysis (CSP) method using the pneumatic spray set-up and compressed air as a carrier gas. Aqueous solutions containing InCl₃ and SC(NH₂)₂ at a molar ratio of In/S = 1/3 and 1/6 were deposited onto preheated glass sheets at substrate temperatures T_s = 205-410 °C. The obtained films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM,) optical transmission spectra, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). According to XRD, thin films deposited at T_s = 205-365 °C were composed of the (0 0 12) orientated tetragonal β-In₂S₃ phase independent of the In/S ratio in the spray solution. Depositions performed at T_s = 410 °C led to the formation of the In₂O₃ phase, preferably when the 1/3 solution was sprayed. Post-deposition annealing in air indicated that oxidation of the sulphide phase has a minor role in the formation of In₂O₃ at temperatures up to 450 °C. In₂S₃ films grown at T_s below 365 °C exhibited transparency over 70% in the visible spectral region and E_g of 2.90-2.96 eV for direct and 2.15-2.30 eV for indirect transitions, respectively. Film thickness and chlorine content decreased with increasing deposition temperatures. The XPS study revealed that the In/S ratio in the spray solution had a significant influence on the content of oxygen (Me-O, BE = 530.0 eV) in the In₂S₃ films deposited in the temperature range of 205-365 °C. Both XPS and EDS studies confirmed that oxygen content in the films deposited using the solution with the In/S ratio of 1/6 was substantially lower than in the films deposited with the In/S ratio of 1/3.     

Preparation and characterization of pulsed laser deposited CdTe thin films at higher FTO substrate temperature and in Ar + O2 atmosphere

Pulsed laser deposition (PLD) is one of the promising techniques for depositing cadmium telluride (CdTe) thin films. It has been reported that PLD CdTe thin films were almost deposited at the lower substrate temperatures (<300 °C) under vacuum conditions. However, the poor crystallinity of CdTe films prepared in this way renders them not conducive to the preparation of high-efficiency CdTe solar cells. To obtain high-efficiency solar cell devices, better crystallinity and more suitable grain size are needed, which requires the CdTe layer to be deposited by PLD at high substrate temperatures (>400 °C). In this paper, CdTe layers were deposited by PLD (KrF, λ = 248 nm, 10 Hz) at different higher substrate temperatures (T_s). Excellent performance of CdTe films was achieved at higher substrate temperatures (400 °C, 550 °C) under an atmosphere of Ar mixed with O₂ (1.2 Torr). X-ray diffraction analysis confirmed the formation of CdTe cubic phase with a strong (1 0 0) preferential orientation at all substrates temperatures on 60 mJ laser energy. The optical properties of CdTe were investigated, and the band gaps of CdTe films were 1.51 eV and 1.49 eV at substrate temperatures of 400 °C and 550 °C, respectively. Scanning electron microscopy (SEM) showed an average grain size of 0.3–0.6 μm. Thus, under these conditions of the atmosphere of Ar + O₂ (15 Torr) and at the relatively high T_s (500 °C), an thin-film (FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe: Cu/Ag) solar cell with an efficiency of 6.68% was fabricated.     

Substrate temperature dependent morphology and resistivity of pulsed laser deposited iridium oxide thin films

Iridium oxide (IrO₂) thin films were deposited on Si (100) substrates by means of pulsed laser deposition technique at various substrate (deposition) temperatures ranging from 250 to 500 °C. Effects of substrate temperature on the crystalline nature, morphology and electrical properties of the deposited films were analyzed by using X-ray diffraction, Raman spectroscopy, Scanning electron microscopy and four-point probe method. It was found that the above properties were strongly dependent on the substrate temperature. The as-deposited films at all substrate temperatures were polycrystalline tetragonal IrO₂ and the preferential growth orientation changed with the substrate temperature. IrO₂ films exhibited fairly homogeneous thickness and good adhesion with the substrate, the average feature size increases with the substrate temperature. The room-temperature resistivity of IrO₂ films decreased with the increase of substrate temperature and the minimum resistivity of (42 ± 6) μΩ cm was obtained at 500 °C. The resistivity of IrO₂ films correlated well with the corresponding film morphology changes.     

Synthesis and characterization of beta barium borate thin films obtained from the BaO-B2O3-TiO2 ternary system

This work reports on the synthesis and the structural and optical characterization of beta barium borate (β-BBO) thin films containing 4, 8 and 16 mol% of titanium oxide (TiO₂) deposited on fused silica and silicon (0 0 1) substrates using the polymeric precursor method. The thin films were characterized by X-ray diffraction, Raman spectroscopy, atomic force microscopy and scanning electron microscopy techniques. The optical transmission spectra of the thin films were measured over a wavelength range of 800-200 nm. A decrease was observed in the band gap energy as the TiO₂ content was raised to 16 mol%. Only the β-BBO phase with a preferential orientation in the (0 0 l) direction was obtained in the sample containing 4 mol% of TiO₂ and crystallized at 650 °C for 2 h.     

Growth and characterization of lead selenide thin films

Growth of lead selenide thin films has been carried out electrochemically on indium doped tin oxide coated conducting glass substrates from an aqueous acidic bath consists of Pb(CH₃COO)₂ and SeO₂. X-ray diffraction analysis has been carried out to determine the crystal structure and phases of the deposited films. Microstructural parameters such as crystallite size, strain and dislocation density which have been evaluated from X-ray diffraction data. Surface morphology and film composition have been analyzed using scanning electron microscopy and energy dispersive analysis by X-rays. The effect of bath temperature on structural, microstructural, morphological and compositional properties of the films are studied and the results are discussed. Optical absorption measurements shows that the deposited films possess a direct band gap value of 0.38?eV.     

Structural and magnetic properties of CoFe2O4 thin films deposited by laser ablation on Si (001) substrates

Cobalt ferrite (CoFe₂O₄) thin films have been deposited on Si (001) substrates, with different substrate temperatures (T_dep = 25 °C − 600 °C). The films were prepared by pulsed laser ablation with a KrF excimer laser (wavelength λ = 248 nm). The oxygen pressure during deposition was 2 × 10⁻² mbar. The films structure was studied by X-ray diffraction (XRD) and their surface was examined by scanning electron microscopy (SEM). The magnetic properties were measured with a vibrating sample magnetometer (VSM). For low deposition temperatures, the films presented a mixture of a CoFe₂O₄ phase, with the cubic spinel structure, and cobalt and iron antiferromagnet oxides with CoO and FeO stoichiometries. As the deposition temperature increased, the CoO and FeO relative content strongly decreased, so that for T_dep = 600 °C the films were composed mainly by polycrystalline CoFe₂O₄. The magnetic hysteresis cycles measured in the films were horizontally shifted due to an exchange coupling field (H_exch) originated by the presence of the antiferromagnetic phases. The exchange field decreased with increasing deposition temperature, and was accompanied by a corresponding increase of the coercivity and remanence ratio of the cycles. This behavior was due to the strong reduction of the CoO and FeO content, and to the corresponding dominance of the CoFe₂O₄ phase on the magnetic properties of the thin films.     

Characteristics of highly orientated BiFeO3 thin films on a LaNiO3-coated Si substrate by RF sputtering

BiFeO₃ (BFO) films were grown on LaNiO₃-coated Si substrate by a RF magnetron sputtering system at temperatures in the range of 300-700 °C. X-ray reflectivity and high-resolution diffraction measurements were employed to characterize the microstructure of these films. For a substrate temperature below 300 °C and at 700 °C only partially crystalline films and completely randomly polycrystalline films were grown, whereas highly (001)-orientated BFO film was obtained for a substrate temperature in the range of 400-600 °C. The crystalline quality of BFO thin films increase as the deposition temperature increase except for the film deposited at 700 °C. The fitted result from X-ray reflectivity curves show that the densities of the BFO films are slightly less than their bulk values. For the BFO films deposited at 300-600 °C, the higher the deposition temperature, the larger the remnant polarization and surface roughness of the films present.     

Structural, dielectric and ferroelectric properties of multilayer lithium tantalate thin films prepared by sol-gel technique

Multilayer lithium tantalate thin films were deposited on Pt-Si [Si(111)/SiO₂/TiO₂/Pt(111)] substrates by sol-gel process. The films were annealed at different annealing temperatures (300, 450 and 650 °C) for 15 min. The films are polycrystalline at 650 °C and at other annealing conditions below 650 °C the films are in amorphous state. The films were characterized using X-ray diffraction, atomic force microscopy (AFM) and Raman spectroscopy. The AFM of images show the formation of nanograins of uniform size (50 nm) at 650 °C. These polycrystalline films exhibit spontaneous polarization of 1.5 μC/cm² at an application of 100 kV/cm. The dielectric constant of multilayer film is very small (6.4 at 10 kHz) as compared to that of single crystal.     

Morphology and growth of e-beam deposited YSZ thin films

Yttria-stabilized zirconium (YSZ) thin films were grown from the tetragonal phase of ZrO₂ stabilized by 8 wt% of Y₂O₃ (8% of YSZ) ceramic powders using e-beam deposition technique (EB-PVD). The influence of the type of substrate on the microstructure of deposited YSZ thin films was analysed. YSZ thin films (2-3 μm of thickness) were deposited on three different types of substrates: optical quartz (SiO₂), porous Ni-YSZ substrates and Alloy 600 (Fe-Ni-Cr). The dependence of the substrate temperature (from 20 to 600 °C) on the thin film structure and the surface morphology were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that (i) the substrate temperature has an influence on the crystallite size, which varied between 12 and 50 nm, (ii) the substrate type has an influence on the growth mechanism of YSZ thin films, and (iii) a bias voltage applied to the substrate during the deposition of thin films has an influence on the densification of YSZ layers.     

Growth and characterization of non-polar ZnO thin films by pulsed laser deposition

Non-polar ZnO thin films were fabricated on r-plane sapphire substrates by pulsed laser deposition at various temperatures from 100 to 500 °C. The effects of the substrate temperature on structural, morphological and optical properties of the films were investigated. Based on the X-ray diffraction analysis, the ZnO thin films grown at 300, 400 and 500 °C exhibited the non-polar (a-plane) orientation and those deposited below 300 °C exhibited polar (c-plane) orientation. In the optical properties of non-polar ZnO films, there were two photoluminescence peaks detected. The peaks (near-band edge emission, blue emission) are due to electron transitions from band-to-band and shallow donor level to valence band, respectively.