Structural, morphological and electrical properties of spray deposited CdIn2Se4 thin films

Semiconducting n-CdIn₂Se₄ thin films have been deposited on to the amorphous and fluorine doped tin oxide (FTO) coated glass substrates using spray pyrolysis technique. The influence of solution concentration on to the photoelectrochemical, structural, morphological, compositional, thermal and electrical properties has been investigated. The PEC characterization shows that the short circuit current (I_sc) and open circuit voltage (V_oc) are at their optimum values (I_sc = 1.04 mA and V_oc = 409 mV) at the optimized precursor concentration (12.5 mM). The structural analysis shows the films are polycrystalline in nature having cubic crystal structure. The average crystallite size determined was in the range of 50-66 nm. Surface morphology and film composition have been analyzed using scanning electron microscopy and energy dispersive analysis by X-rays, respectively. The addition of solution concentration induces a decrease in the electrical resistivity of CdIn₂Se₄ films up to 12.5 mM solution concentration. The type of semiconductor was examined from thermoelectric power measurement.     

Influence of indium doping on the properties of spray deposited CdS0.2Se0.8 thin films

Polycrystalline indium doped CdS_0.2Se_0.8 thin films with varying concentrations of indium have been prepared by spray pyrolysis at 300 °C. The as deposited films have been characterized by XRD, AFM, EDAX, optical and electrical resistivity measurement techniques. The XRD patterns show that the films are polycrystalline with hexagonal crystal structure irrespective of indium doping concentration. AFM studies reveal that the RMS surface roughness of film decreases from 34.68 to 17.76 with increase in indium doping concentration up to 0.15 mol% in CdS_0.2Se_0.8 thin films and further it increases for higher indium doping concentrations. Traces of indium in CdS_0.2Se_0.8 thin films have been observed from EDAX studies. The optical band gap energy of CdS_0.2Se_0.8 thin film is found to decrease from 1.91 eV to 1.67 eV with indium doping up to 0.15 mol% and increase after 0.15 mol%. The electrical resistivity measurement shows that the films are semiconducting with minimum resistivity of 3.71 × 10⁴ Ω cm observed at 0.15 mol% indium doping. Thermoelectric power measurements show that films exhibit n-type conductivity.     

Structural, optical and electrical properties of CuIn5S8 thin films grown by thermal evaporation method

Stoichiometric compound of copper indium sulfur (CuIn₅S₈) was synthesized by direct reaction of high purity elemental copper, indium and sulfur in an evacuated quartz tube. The phase structure of the synthesized material revealed the cubic spinel structure. The lattice parameter (a) of single crystals was calculated to be 10.667 Å. Thin films of CuIn₅S₈ were deposited onto glass substrates under the pressure of 10⁻⁶ Torr using thermal evaporation technique. CuIn₅S₈ thin films were then thermally annealed in air from 100 to 300 °C for 2 h. The effects of thermal annealing on their physico-chemical properties were investigated using X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), optical transmission and hot probe method. XRD studies of CuIn₅S₈ thin films showed that as-deposited films were amorphous in nature and transformed into polycrystalline spinel structure with strong preferred orientation along the (3 1 1) plane after the annealing at 200 °C. The composition is greatly affected by thermal treatment. From the optical transmission and reflection, an important absorption coefficient exceeds 10⁴ cm⁻¹ was found. As increasing the annealing temperature, the optical energy band gap decreases from 1.83 eV for the as-deposited films to 1.43 eV for the annealed films at 300 °C. It was found that CuIn₅S₈ thin film is an n-type semiconductor at 300 °C.     

Optical properties of thermally evaporated Bi2Se3 thin films treated with AgNO3 solution

Bismuth selenide (Bi₂Se₃) thin films have been prepared onto clean glass substrates by the thermal evaporation technique. The deposited films were then immersed in silver nitrate solution for different periods of time, followed by annealing in Argon atmosphere at 473 K for 1 h, to obtain Ag/Bi₂Se₃ samples. The prepared films have been examined by X-ray and transmission electron microscopy for structural determination. The optical transmission and reflection spectra of the deposited films have been recorded within the wavelength range 400-2500 nm. The variation of the optical parameters of the prepared films, such as refractive index, n, and the optical band gap, E_g as a function of the immersion duration times has been determined. The refractive index dispersion in the transmission and low absorption region is adequately described by the well-known Sellmeier dispersion relation, whereby the values of the oscillator strength, oscillator position, the high-frequency dielectric constant, ε_∞ as well as the carrier concentration to the effective mass ratio, N/m* were calculated as a function of the immersion duration time.     

Synthesis and optical properties of yttria-doped ZrO2 nanopowders

Yttria-doped zirconia (YDZ) nanopowders were synthesized via a solvothermal route using ethanol as solvent. Evolution of crystal phases for different amount of yttria-doped samples were studied by X-ray diffraction (XRD). Morphology and component of the as-synthesized cubic YDZ were characterized by scanning electron microscopy (SEM) and energy dispersion spectrum (EDS). Defects of the sample were detected using ultraviolet–vis (UV–vis) absorption spectrum and photoluminescence (PL) spectrum. The results indicated that cubic structured nanocrystals can be obtained through doping 4 mol% Y₂O₃ into ZrO₂ lattice. The particles had sphere morphology with an average crystal size of 10 nm and agglomerated into bigger spheres with a diameter of about 120 nm. Mechanism of the agglomeration was also discussed. UV spectra showed two absorption peaks, red shift for both of the adsorption edges was observed. PL spectra with excitation wavelength of 260 and 420 nm revealed six fluorescence peaks which were regarded as various energy levels in the band gap and as the evidence of existence of oxygen vacancies in the as-synthesized sample.     

Crystal structures of the Ag4HgGe2S7 and Ag4CdGe2S7 compounds

The crystal structures of the Ag₄HgGe₂S₇ and Ag₄CdGe₂S₇ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the monoclinic Cc space group with the lattice parameters a=1.74546(8), b=0.68093(2), c=1.05342(3) nm, β=93.398(3)° for Ag₄HgGe₂S₇ and a=1.74364(8), b=0.68334(3), c=1.05350(4) nm, β=93.589(3)° for Ag₄CdGe₂S₇. Atomic parameters were refined in the isotropic approximation (R_I=0.0761 and R_I=0.0727, respectively).     

Effect of Ag nanoparticle size on the plasmonic photocatalytic properties of TiO2 thin films

Photocatalytic TiO₂ films combined with Ag nanoparticles (NPs) embedded-SiO₂ films were fabricated by means of a RF magnetron sputtering and subsequent rapid thermal annealing (RTA). X-ray diffraction results show that the TiO₂ films have anatase phase when annealed at 500 °C. The Ag NPs were formed by deposition and subsequent annealing at 600 °C. Scanning electron microscopy (SEM) results show that the density of the NPs decreases with increasing Ag film thickness. For example, the average NP diameter varies from ~ 19.3 to ~ 55.9 nm as the film thickness increases from 2 to 12 nm. Transmittance measurements show that as the Ag NP size decreases, the plasmonic peaks shift towards the shorter-wavelength region and become narrower. It is further shown that under UV-illumination (352 nm), all the TiO₂ films with the Ag NPs show higher methylene blue decomposition rates compared to the TiO₂ only films and the TiO₂ films with Ag NP (a 7 nm-thick Ag film) show the best decomposition rate among the samples possibly due to the combined effects of optimized localized field amplification and radiative efficiency.     

Structural, morphological and electrical properties of spray deposited nano-crystalline CeO2 thin films

Nanocrystalline, uniform, dense, and adherent cerium oxide (CeO₂) thin films have been successfully deposited by a simple and cost effective spray pyrolysis technique. CeO₂ films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. Films were characterized by differential thermal analysis, X-ray diffraction, scanning electron microscopy, atomic force microscopy; two probe resistivity method and impedance spectroscopy. X-ray diffraction analysis revealed the formation of single phase, well crystalline thin films with cubic fluorite structure. Crystallite size was found to be in the range of 10-15 nm. AFM showed formation of smooth films with morphological grain size 27 nm. Films were found to be highly resistive with room temperature resistivity of the order of 10⁷ Ω cm. Activation energy was calculated and found to be 0.78 eV. The deposited film showed high oxygen ion conductivity of 5.94 × 10⁻³ S cm⁻¹ at 350 °C. Thus, the deposited material shows a potential application in intermediate temperature solid oxide fuel cells (IT-SOFC) and might be useful for μ-SOFC and industrial catalyst applications.     

Structural, optical and electrical properties of Mg-doped CuCrO2 thin films by sol-gel processing

CuCr_1−xMg_xO₂ (x = 0, 0.03, 0.05, 0.07) thin films were prepared on sapphire substrates by sol-gel processing. The effect of Mg concentrations on the structural, morphological, electrical and optical properties was investigated. Highly transparent ≧70% Mg-doped CuCrO₂ thin films with p-type conduction and semiconductor behavior were obtained. The microstructure of the systems was characterized by scanning electron microscopy and the roughness increased as the content of Mg increased. The photoluminescence spectra results indicated that it had a green luminescent emission peak at the 530 nm. In this paper, CuCr_0.95Mg_0.05O₂ film has the lowest resistivity of 7.34 Ω cm with direct band gap of 3.11 eV. In order to investigate the conduction mechanism, the energy band of the CuCrO₂ films is constructed based on the grain-boundary scattering.     

Electrical and electrochemical properties of γ-Li2CuZrO4

The γ-Li₂CuZrO₄ with a double rock-salt structure, as a lithium-ion compound, has never been reported on their physical and physicochemical properties. The γ-Li₂CuZrO₄ was prepared by a solid-state reaction process. X-ray diffraction was used to analyze the structure of the products. Its electrical properties were characterized by both DC and AC measurements in the temperature range from 133 to 1273 K. Cyclic voltammetry and galvanostatic cell cycling were also employed to evaluate its electrochemical performance. It is found to be a pure electronic semiconductor with a fairly high conductivity (10⁻⁵ S/cm at 133 K, 10⁻² S/cm at 300 K and 10⁻¹ S/cm at 1173 K). The average activation temperature is 14.4 kJ/mol. When increasing the temperature above 1073 K, a phase transition from γ to β takes place. When reacting with lithium in an electrochemical cell, γ-Li₂CuZrO₄ decomposes into three phases during the initial discharge process, and possesses a reversible capacity of about 70 mAh/g.     

Mechanochemical solid state synthesis of (Cd0.8Zn0.2)S quantum dots: Microstructure and optical characterizations

(Cd_0.8Zn_0.2)S quantum dots with a mixture of both cubic (Zinc-blende) and hexagonal (Wurtzite) phases have been prepared within 75 min by mechanical alloying the stoichiometric mixture of Cd, Zn and S powders at room temperature in a planetary ball mill under Ar. The Rietveld analysis of X-ray powder diffraction data reveals relative phase abundances of both cubic and hexagonal phases and several microstructure parameters like lattice parameters, particle sizes, lattice strains, concentrations of different kinds of stacking faults, etc. in both the phases. At the time of formation, hexagonal phase dominates over the cubic phase (molar ratio ∼0.6:0.4), but in course of milling up to 15 h, the hexagonal phase partially transforms to cubic phase and the molar ratio becomes ∼0.4:0.6. Particle sizes of hexagonal and cubic phases reduce to ∼4.5 nm and 12.5 nm, respectively, after 15 h of milling. The hexagonal phase contains a significant amount of lattice strain in comparison to cubic phase. The presence of different kinds of stacking faults is revealed clearly from the high resolution transmission electron microscope (HRTEM) images.     

Solvothermal synthesis of Hg1−xCdxTe nanostructures—Their structural and optical properties

This article describes a facile, low-cost, solution-phase approach to the large-scale preparation of Hg_1−xCd_xTe nanostructures of different shapes such as nanorods, quantum dots, hexagonal cubes of different sizes and different compositions at a growth temperature of 180 °C using an air stable Te source by solvothermal technique. The XRD spectrum shows that the crystals are cubic in their basic structure and reveals the variation in lattice constant as a function of composition. The size and morphology of the products were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The formation of irregular shaped particles and few nano-rods in the present synthesis is attributed to the cetyl trimethylammonium bromide (CTAB). The room temperature FTIR absorption and PL studies for a compositon of x = 0.8 gives a band gap of 1.1 eV and a broad emission in NIR region (0.5-0.9 eV) with all bands attributed to surface defects.     

Effects of lanthanum doping on the preferred orientation, phase structure and electrical properties of sol-gel derived Pb1-3x/2Lax (Zr0.6Ti0.4)O3 thin films

Pb_1-3x/2La_x (Zr_0.6Ti_0.4)O₃ thin films (0 ≤ x ≤ 0.08) were prepared on the Pt (1 1 1)/Ti/SiO₂/Si (1 0 0) substrates by a sol-gel method. The morphology, preferred orientation, phase structure, dielectric and ferroelectric properties of the films have been investigated. Our results show that lanthanum doping is favorable to enhance crystalline and obtain (1 0 0)-preferred orientation of the films. Meanwhile, it is suggested that the films undergo a structure change from “rhombohedral” phase to monoclinic phase as the lanthanum-doped content is increased to x ≈ 0.05. Results of dielectric properties and ferroelectric properties indicate that lanthanum doping contributes to improve film dielectric constant and dielectric loss while it brings about a striking decrease in remnant polarization value. Possible explanations for the variations of electrical properties have been discussed in terms of preferred orientation, phase structure and large lattice distortion.     

Effects of Mg substitution on the structural, optical, and electrical properties of CuAlO2 thin films

Mg-doped CuAlO₂ thin films are prepared by the chemical solution method. The XRD results show that the solid solubility of Mg species on Al sites in CuAlO₂ lattice is lower than 2 at.%. When less than 2 at.% of Mg is added to the CuAlO₂ film, the surface roughness of the films was reduced with Mg substitution. Moreover, the c-axis orientation of the films improves because the in-plane fusion between CuAlO₂ crystallites is hindered. Optical and electrical measurements show that substituting Al³⁺ in the films with Mg²⁺ increases both their transmittance in the visible region and their optical band gaps. As well, their electrical conductivity is enhanced. At 300 K, the conductivity of the 1 at.% Mg-doped sample is up to 5.2 × 10⁻³ S/cm. Thus, Mg-doped CuAlO₂ films may have potential applications as transparent conductive oxides.     

Structural and mechanical properties of nanostructured TiO2 thin films deposited by RF sputtering

This study mainly aims to evaluate the effects of substrate temperatures on the mechanical properties of TiO₂ thin films deposited on glass substrates by radio-frequency (RF) magnetron sputtering. All titania films possess anatase structure having a nodular morphology. AES results reveal that Si and Na ions from glass diffuse into TiO₂ films at higher substrate temperatures. Micro-scratch and wear tests were conducted to evaluate their mechanical and tribological properties. The adhesion critical loads of TiO₂ films deposited at room temperature, 200 and 300 °C are found to be 1.51, 1.54 and 1.08 N, respectively. Scratch hardness also increases from 11.5 to 13.6 GPa with increasing temperature. The wear track width decreases with substrate temperature indicating an improved wear resistance at higher temperatures.     

Synthesis, structure and optical properties of CoAl2O4 spinel nanocrystals

CoAl₂O₄ nanocrystals were synthesized by sol-gel method using citric acid as a chelating agent at low temperature. The as-synthesized samples were characterized by thermal analysis, X-ray powder diffraction, infrared spectroscopy and transmission electron microscopy. The results show that CoAl₂O₄ spinel is the only crystalline phase with a size of 10-30 nm in the temperature range 500-1000 °C. The temperature dependence of the distribution of Al³⁺ and Co²⁺ ions in the octahedral and tetrahedral sites in nanocrystals was investigated by X-ray photoelectron spectroscopy (XPS). It is observed that the inversion parameter decreases with increasing annealing temperature. Analysis of the absorption properties indicates that Co²⁺ ions are located in the tetrahedral sites as well as in the octahedral sites in the CoAl₂O₄ nanocrystals. The origin of the green color (300-500 nm absorption band) should be due to the octahedrally coordinated Co²⁺ ions.     

Annealing driven performance and optical effects in nanocrystalline SnO2 thin films induced by pulsed delivery

Tin dioxide thin films were prepared successfully by pulsed laser deposition techniques on glass substrates. The thin films were then annealed for 30 min from 50 °C to 550 °C at 50 °C intervals. The influence of the annealing temperature on the microstructure and optical properties of SnO₂ thin films was investigated using X-ray diffraction, optical transmittance and reflectance measurements. Various optical parameters, such as optical band gas energy, refractive index and optical conductivity were calculated from the optical transmittance and reflectance data recorded in the wavelength range 300-2500 nm. We found that the SnO₂ thin film annealed at temperatures up to 400 °C is a good window material for solar cell application. Our experimental results indicated that SnO₂ thin films with the high optical quality could be synthesized by pulsed laser deposition techniques.     

Preparation of delafossite-type CuCrO2 films by sol-gel method

High-quality c-axis oriented delafossite-type CuCrO₂ films were successfully prepared by a simple sol-gel method. The microstructure, optical properties as well as room temperature resistivity were studied. It was found that the grain sizes of CuCrO₂ films pretreated with different temperatures are different; the films were smooth and consisted of fine particles. The maximal transmittance of CuCrO₂ films can reach 70% in the visible region. Optical transmission data of CuCrO₂ films indicate a direct band gap and an indirect-gap of about 3.15 eV and 2.66 eV, respectively. The carrier mobility of the films pretreated at 300 °C is smaller than that of the films pretreated at a higher temperature, because of the stronger carrier scattering.     

Synthesis and characterization of Cu2ZnSnS4 thin films grown by PLD: Solar cells

As-deposited and annealed Cu₂ZnSnS₄ (CZTS) thin films have been synthesized onto Mo coated glass substrates at different deposition times using pulsed laser deposition (PLD) technique. The effect of deposition time (film thickness) and annealing onto the structural, morphological, compositional and optical properties of CZTS thin films have been investigated. The polycrystalline CZTS thin films with tetragonal crystal structure have been observed from structural analysis. FESEM and AFM images show the smooth, uniform, homogeneous and densely packed grains and increase in the grain size after annealing. The internal quantitative analysis has been carried out by XPS study which confirms the stoichiometry of the films. The optical band gap of CZTS films grown by PLD is about 1.54 eV, which suggests that CZTS films can be useful as an absorber layer in thin film solar cells. Device performance for deposited CZTS films has been studied.     

Physical properties of tin oxide thin films improved by vapour chopping

The vapour chopping technique has been successfully used to lower the ambient air ageing effect on the tin oxide thin films. The films were prepared by thermal oxidation (in air) of vacuum evaporated vapour chopped and nonchopped tin thin films. The films showed SnO and SnO₂ phases with tetragonal and orthorhombic structure. All the films showed increase in optical transmittance with increase in oxidation temperature and duration. The vapour chopped films showed higher refractive index and band gap than those of nonchopped films. The refractive index was found to increase with the thickness. Due to air ageing, the refractive index of both the films was found to increase. The ageing effect was found lower on the vapour chopped (0.008) than those on nonchopped (0.02) tin oxide thin films. These films can have potential use in optical waveguides.