Substrate temperature effect on the optical properties of amorphous Sb2S3 thin films

Sb₂S₃ amorphous thin films were prepared by thermal evaporation of corresponding powder on thoroughly cleaned glass substrates held at temperature in the range 300‐473 K. X‐ray diffraction and atomic force microscopy have been used to order to identify the structure and morphology of surface thin films. The optical constants of the deposition films were obtained from the analysis of the experimental recorded transmission data over the wavelength range 400‐1400 nm. An analysis of the absorption coefficient values revealed an optical indirect transition with the estimation of the corresponding band gap values. It was found that the optical band gap energy decrease with substrate temperature from 1.67 eV at 300 K to 1.48 eV at 473K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Substrate effect on microstructure and optical performance of sputter‐deposited TiO2 thin films

This study deals with the role of the different substrates on the microstructural, optical and electronical properties of TiO₂ thin films produced by conventional direct current (DC) magnetron sputtering in a mixture of pure argon and oxygen using a Ti metal target with the aid of X–ray diffractometer (XRD), ultra violet spectrometer (UV–vis) and atomic force microscopy (AFM) measurements. Transparent TiO₂ thin films are deposited on Soda lime glass, MgO(100), quartz and sitall substrates. Phase purity, surface morphology, optical and photocatalytic properties of the films are compared with each other. It is found that the amplitude of interference oscillation of the films is in a range of 77‐89%. The transmittance of the film deposited on Soda lime glass is the smallest while the film produced on MgO(100) substrate obtains the maximum transmittance value. The refractive index and optical band gap of the TiO₂ thin films are also inferred from the transmittance spectra. The results show that the film deposited on Soda lime glass has the better optical property while the film produced on MgO(100) substrate exhibits much better photoactivity than the other films because of the large optical energy band gap. As for the XRD results, the film prepared on MgO(100) substrate contains the anatase phase only; on the other hand, the other films contain both anatase and rutile phases. Furthermore, AFM images show that the regular structures are observed on the surface of all the films studied. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of thermoannealing on crystallinity and optical properties of Sb2S3 thin films

Sb₂S₃ thin films are obtained by evaporating of Sb₂S₃ powder onto glass substrates maintained at room temperature under pressure of 2×10^‐5 torr. The composition of the thin films was determined by energy dispersive analysis of X‐ray (EDAX). The effect of thermal annealing in vacuum on the structural properties was studied using X‐ray diffraction (XRD) technique and scanning electron microscopy (SEM). The as‐deposition films were amorphous, while the annealed films have an orthorhombic polycrystalline structure. The optical constants of as‐deposited and annealed Sb₂S₃ thin films were obtained from the analysis of the experimental recorded transmission spectral data over the wavelength range 400‐1400 nm. The transmittance analysis allowed the determination of refractive index as function of wavelength. It was found that the refractive dispersion data obeyed the single oscillator model, from which the dispersion parameters (oscillator energy, E₀, dispersion energy, E_d) were determined. The static refractive index n(0), static dielectric constant, ε_∞, and optical band gap energy, E_g, were also calculated using the values of dispersion parameters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of oxygen partial pressure on physical properties of nano‐crystalline silver oxide thin films deposited by RF magnetron sputtering

Nano‐crystalline silver oxide films were deposited on glass and silicon substrates held at room temperature by RF magnetron sputtering of silver target under different oxygen partial pressures. The influence of oxygen partial pressure on the structural, morphological, electrical and optical properties of deposited films was investigated. Varying oxygen partial pressure during the sputter deposition leads to changes of mixed phase of Ag₂O and Ag to a single phase of Ag₂O and to AgO. The X‐ray diffraction and X‐ray photoelectron spectroscopy results showed the formation of single phase Ag₂O with cubic structure at oxygen partial pressures of 2x10^‐2 Pa while the films deposited at higher oxygen partial pressure of 9x10^‐2 Pa showed the formation of single phase of AgO with monoclinic structure. Raman spectroscopic studies on the single phase Ag₂O showed the stretching vibration of Ag‐O bonds. Single‐phase Ag₂O films obtained at oxygen partial pressure of 2x10^‐2 Pa were nano‐crystalline with crystallite size of 20 nm and possessed an electrical resistivity of 5.2x10^‐3 Ωcm and optical band gap of 2.05 eV. The films deposited at higher oxygen partial pressure of 9x10^‐2 Pa were of AgO with electrical resistivity of 1.8x10^‐2 Ωcm and optical band gap of 2.13 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,compositional and optical properties of gallium selenide thin films doped with cadmium

Polycrystalline cadmium doped gallium selenide thin films were obtained by the thermal co‐evaporation of GaSe crystals and Cd grains onto glass substrates. The structural, compositional and optical properties of these films have been investigated by means of X‐ray diffraction, energy dispersive X‐ray analysis and UV‐visible spectroscopy techniques, respectively. Particularly, the elemental analysis, the crystalline nature, the energy band gap, the refractive index, the dispersion energy and static dielectric constant have been identified. The absorption coefficient spectral analysis in the sharp absorption region revealed a direct forbidden energy band gap of 1.22 eV. The cadmium doping has caused a significant decrease in the values of the energy band gap and in all the dispersive optical parameters, as well. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and structural characterisation of zinc oxide thin films prepared by sol‐gel process

Zinc oxide thin films have been prepared on different substrates by the sol‐gel method using 2‐methoxyethanol solution of zinc acetate dihydrate stabilized by monoethanolamine. The photoluminescence spectra of the films show the band‐edge and sub‐band transitions. The intensity of the band edge emission peak increases, while the intensity of the deep level emission peak decreases in the films coated on sapphire substrate. Transmittance spectra show that the films are transparent beyond 400 nm. The structural property of the films has been evaluated using X‐ray diffraction. The X‐ray peak intensity of the film (002) grown on sapphire substrate is higher than the films grown on glass and quartz substrates. The AFM images show improvement in the surface of the annealed films as compared to the as‐grown ZnO films coated on sapphire substrates. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Properties of Sm‐doped CaNb2O6 thin films deposited by radio‐frequency magnetron sputtering

Sm‐doped CaNb₂O₆ (CaNb₂O₆:Sm) phosphor thin films were prepared by radio‐frequency magnetron sputtering on sapphire substrates. The thin films were grown at several growth temperatures and subsequently annealed at 800 °C in air. The crystallinity, surface morphology, optical transmittance, and photoluminescence of the thin films were investigated by X‐ray diffraction, scanning electron microscopy, ultraviolet‐visible spectrophotometry, and fluorescence spectrophotometry, respectively. All of the thin films showed a main red emission radiated by the transition from the ⁴G_5/2 excited state to the ⁶H_9/2 ground state of the Sm³⁺ ions and several weak bands under ultraviolet excitation with a 279 nm wavelength. The optimum growth temperature for depositing the high‐quality CaNb₂O₆:Sm thin films, which was determined from the luminescence intensity, was found to be 400 °C, where the thin film exhibited an orthorhombic structure with a thickness of 370 nm, an average grain size of 220 nm, a band gap energy of 3.99 eV, and an average optical transmittance of 85.9%. These results indicate that the growth temperature plays an important role in controlling the emission intensity and optical band gap energy of CaNb₂O₆:Sm thin films.     

Temperature dependence of growth orientation and surface morphology of Li‐doped ZnO thin films on SiO2/Si substrates

ZnO thin films doped with Li (ZnO:Li) were deposited onto SiO₂/Si (100) substrates by direct‐current sputtering technique in the temperature range from room temperature to 500 °C. The crystalline structure, surface morphology and composition, and optical reflectivity of the deposited films were studied by X‐ray diffraction (XRD), Scanning Electron Microscopy (SEM), X‐ray Photoelectron Spectroscopy (XPS) and optical reflection measurements. Rough surface p‐type ZnO thin film deposition was confirmed. The results indicated that the ZnO:Li films growed at low temperatures show c‐axis orientation, while a‐axis growth direction is preferable at high temperatures. Moreover, the optical reflectivity from the surface of the films matched very well with the obtained results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Cu/In ratio on properties of CuInSe2 thin films prepared by selenization of Cu‐In layers

In this paper, the chalcopyrite CuInSe2 thin films were fabricated from a selenization of electrodeposited Cu‐In layers. In this study, the electrodeposition time of the In layer was set, but that for the Cu layer was not. The thin films were selenized in a sealed glass tube with pure Se powder by three different Cu layer samples at various electrodeposition times at 500 °C for 2 hours. An FE‐SEM image of the sample shows that the copper‐rich product has irregular agglomerates with a dense surface. The X‐ray diffraction patterns show CuInSe₂ peaks for all samples. However, the X‐ray diffraction pattern reveals CuSe₂ peaks when the electrodeposition time of the Cu layer increases. On the other hand, the band gap (E_g) of the samples decreases from 1.15 to 1.07 eV when the Cu/In ratio increases.     

Synthesis and optical properties of CuInS2 thin films prepared by sulfurization of electrodeposited Cu‐In layers

The chalcopyrite CuInS₂ thin film was fabricated at 500 °C for 2 h by sulfurization of Cu‐In layers (as precursors) that were sulfurized in a glass tube with pure sulfur powder. The structural, morphological, and optical properties of CuInS₂ thin films are characterized using X‐ray diffraction (XRD), field‐emission scanning electron microscope (FE‐SEM), and UV/Visible/NIR spectrophotometer. The study of UV/Visible/NIR absorption shows the band gap energy value of CuInS₂ thin films is 1.5 eV. The XRD pattern shows the film is pure CuInS₂; no other peaks, such as CuS or CuIn₅S₈ were observed. Furthermore, the surface of the CuInS₂ film is compact characterized by FE‐SEM, which also shows the disappearance of CuS on the surface at 500 °C.     

Optical and structural properties of lead iodide thin films prepared by vacuum evaporation method

Thermally processed lead iodide (PbI₂) thin films were prepared by the vacuum evaporation method in a constant ambient. Measured thickness of the film was verified analytically from the optical transmittance data in a wavelength range between 300 and 1600 nm. From the Tauc relation for the non‐direct inter band transition, the optical band gap of the film was found to be 2.58 eV for film thickness 300 nm. X‐ray diffraction analysis confirmed that PbI₂ films are polycrystalline, having hexagonal structure. The low fluctuation in Urbach energy indicates that the grain size is quite small. The present findings are in agreement with the other results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of substrate temperature on microcrystalline structure and optical properties of ZnTe thin films

ZnTe thin films were deposited onto well‐cleaned glass substrates kept at different temperatures (Ts = 303, 373 and 423 K), by vacuum evaporation method under the pressure of 10^–5 Torr. The thickness of the film was measured by quartz crystal monitor and verified by the multiple beam interferometer method. The structural characterization was made using X‐ray diffractometer with filtered CuKα radiation. The grain sizes of the microcrystallines in films increases with increase in substrate temperature. The strain (ε), grain size (D) and dislocation density (δ) was calculated and results are discussed based on substrate temperature. Optical behaviour of the film was analyzed from transmittance spectra in the visible region (400–800 nm). The optical transition in ZnTe films is direct and allowed type. The optical band gap energy shows an inverse dependence on substrate temperature and thickness. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of substrate temperature on polycrystalline Cd0.9Zn0.1Te thin films studied by Raman scattering spectroscopy

Cd_0.9Zn_0.1Te thin films were prepared by vacuum evaporation onto well‐cleaned glass substrates maintained at 300, 373 and 473 K. X‐ray diffraction studies revealed that the films have zinc blende structure with preferential (111) orientation. Raman peak of the room temperature deposited film appeared at 140.30 cm^‐1 and 159.65 cm^‐1 were for the transverse optic (TO) and longitudinal optic (LO) phonons respectively. The XRD patterns of the higher substrate temperature deposited films exhibited an improvement in the crystallinity of the films. The Raman peak intensity increases and the FWHM decreases for the films deposited at higher substrate temperature. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of substrate temperature on the properties of reactively sputtered TiN/NbN multilayers

TiN/NbN multilayer coatings were deposited with various substrate temperatures by DC reactive magnetron sputtering method onto Si (111) and glass substrates. The effect of substrate temperature on the structural and optical properties of TiN/NbN multilayers was investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, Field emission scanning electron microscopy and Photoluminescence measurements. The composition was analyzed by X‐ray photoelectron spectroscopy. X‐ray diffraction results showed that the layers crystallized in cubic structure for TiN and hexagonal structure for NbN. It was found that grain size increased with increase in substrate temperature. The surface morphology of the TiN/NbN thin films showed a dense and smooth surface with substrate temperature upto 200 °C but after 300 °C, the grains became larger and coarse surface was observed. The TiN/NbN multilayer coatings exhibited the characteristic peaks centered at 180, 210 and 560 cm^‐1. Red band emission peaks were observed in the wavelength range of 700‐710 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of temperature on the microcrystalline structure of thermally evaporated Sb2S3 thin films

Thin films of antimony trisulfide (Sb₂S₃) were prepared by thermal evaporation under vacuum (p=5×10^–5 torr) on glass substrates maintained at various temperatures between 293 K and 523 K. Their microstructural properties have obtained by transmission electron microscopy (TEM). The electron diffraction analysis showed the occurrence of amorphous to polycrystalline transition in the films deposited at higher temperature of substrates (523 K). The polycrystalline thin films were found to have an orthorhombic structure. The interplanar distances and unit‐cell parameters were determined by high‐resolution transmission electron microscopy (HRTEM) and compared with the standard values for Sb₂S₃. The surface morphology of Sb₂S₃ thin films was investigated by scanning electron microscopy (SEM). The optical transmission spectra at normal incidence of Sb₂S₃ thin films have been measured in the spectral range of 400–1400 nm. The analysis of the absorption spectra revealed indirect energy gaps, characterizing of amorphous films, while the polycrystalline films exhibited direct energy gap. From the photon energy dependence of absorption coefficient, the optical band gap energy, E_g, were calculated for each thin films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of annealing temperature on the structural and optical properties of amorphous Sb2Te2Se thin films

Thin films of Sb₂Te₂Se were prepared by conventional thermal evaporation of the presynthesized material on Corning glass substrates. The chemical composition of the samples was determined by means of energy‐dispersive X‐ray spectrometry. X‐ray diffraction studies on the as‐deposited and annealed films revealed an amorphous‐to‐crystalline phase transition. The as‐deposited and annealed films at T _a = 323 and 373 K are amorphous, while those annealed at T _a= 423 and 473 K are crystalline with a single‐phase of a rhombohedral crystalline structure as that of the source material. The unit‐cell lattice parameters were determined and compared with the reported data. The optical constants (n , k ) of the investigated films were determined from the transmittance and reflectance data at normal incidence in the spectral range 400–2500 nm. The analysis of the absorption spectra revealed non‐direct energy gaps, characterizing the amorphous films, while the crystalline films exhibited direct energy gaps. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

TiO2 thin films as sensing gas materials

TiO₂ thin films were prepared by DC reactive magnetron sputtering on heated Si, quartz and glass substrates using O₂ and water vapor as reactive gases. The percentage of anatase and rutile as well as the grain size strongly depend on the deposition conditions, as revealed by X-ray diffraction patterns. The films deposited on Si substrates are pure rutile, while a mixed anatase/rutile structure occurs in the films deposited on glass and quartz substrates. Smaller grain rutile and anatase films were prepared in a water vapor atmosphere, in contrast to the films grown in oxygen. The former choice considerably increases the sensing properties of titanium dioxide films. The gas sensitivity was investigated for some reducing gases (methane, acetone, ethanol and liquefied petroleum gas) and the optimum operating temperatures were found.     

Characterization of Vacuum Evaporated Polycrystalline Cd0.96Zn0.04Te Thin Films by XRD,Raman Scattering and Spectroscopic Ellipsometry

Cd_0.96Zn_0.04Te thin films are deposited onto well cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation and the films are annealed at 423 K. Rutherford Backscattering Spectrometry and X‐ray diffraction techniques are used to determine the thickness, composition and crystalline structure and grain size of the films respectively. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the as‐deposited films is 3.7 nm and on annealing the films at 423K, the rms roughness value decreases to 3.4 nm. The Raman spectra of the Cd_0.96Zn_0.04Te films are recorded at room temperature to study lattice vibrations and their interactions with other excitations. The intensity of the peak increases and the FWHM decreases on annealing the films. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E), of polycrystalline Cd_0.96Zn_0.04Te thin films in the 1.3 ‐ 5.5eV photon energy range at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+Δ₁ and E₂ critical points are due to interband transitions.     

Optical characterization of thermally evaporated thin CdO films

Cadmium Oxide films have been prepared by vacuum evaporation method on a glass substrate at room temperature. Detailed structural, optical, and electrical properties of the films are presented at different annealing temperatures. The crystal structure of the samples was studied by X‐ ray diffraction. The spectral absorption coefficient of the CdO film at the fundamental absorption region (450‐650nm) was determined using the spectral data of transmittance. The direct and indirect band gap energies were determined and found to be 2.33 eV and 1.95 eV respectively. The third order optical nonlinearities χ(3) of CdO films has been measured used the z‐can technique. The real and imaginary parts of χ(3) have been measured at 514 nm and found to be 1.7x10^‐3 esu and 3.0x10^‐3 esu, respectively. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of substrate temperature on the properties of vacuum evaporated indium selenide thin films

Thin films of InSe were obtained by thermal evaporation techniques on glass substrates maintained at various temperatures (T_sb = 30°, 400°C). X‐ray diffraction analysis showed the occurrence of amorphous to polycrystalline transformation in the films deposited at higher substrate temperature (400°C). The polycrystalline films were found to have a hexagonal lattice. Compositions of these films have been characterized by EDAX and the surface analysis by scanning electron microscopy. Optical properties of the films, investigated by using spectrophotometer transmittance spectra in the wavelength range (300 – 1100 nm), were explained in terms of substrate temperatures. Films formed at room temperature showed an optical band gap (E_g^opt) 1.56 eV; where as the films formed at 400°C were found to have a E_g^opt of 1.92 eV. The increase in the value of E_g^opt with T_sb treatment is interpreted in terms of the density of states model as proposed by Mott and Davis. The analysis of current ‐Voltage characteristics, based on space charge limited currents (SCLC) measurements, confirms the exponential decrease of density of states from the conduction band edge towards the Fermi level for both the amorphous and polycrystalline films. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)