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1.
Pulsed laser deposited nanocrystalline V 2O 5 thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and optical spectroscopy. The films were deposited on amorphous glass substrates, keeping the O 2 partial pressure at 13.33 Pa and the substrate temperature at 220 °C. The characteristics of the films were changed by varying the laser fluence and repetition rate. XRD revealed that films are nanocrystalline with an orthorhombic structure. XPS shows the sub-stoichiometry of the films, that generally relies on the fact that during the formation process of V 2O 5 films, lower valence oxides are also created. From the HRTEM images, we observed the size evolution and distribution characteristics of the clusters in the function of the laser fluence. From the spectral transmittance we determined the absorption edge using the Tauc plot. Calculation of the Bohr radius for V 2O 5 is also reported. 相似文献
2.
The metal-insulator transition in vanadium dioxide thin films implanted with O + ions was studied. Ion implantation lowered the metal-insulator transition temperature of the VO 2 films by 12 °C compared to the unimplanted ones, as measured both optically and electrically. The lowering of the transition temperature was accomplished without significantly reducing the mid-wave infrared optical transmission in the insulating state for wavelengths > 4.3 μm. Raman spectroscopy was used to examine changes to the crystalline structure of the implanted films. The Raman spectra indicate that ion implantation effects are not annealed out for temperatures up to 120 °C. 相似文献
3.
The electrical and dielectric properties of reactively sputtered Ta 2O 5 thin films with Cu as the top and bottom electrodes forming a simple metal insulator metal (MIM) structure, Cu/Ta 2O 5/Cu/n-Si, were studied. Ta 2O 5 films subjected to rapid thermal annealing (RTA) at 800°C for 30 s in N 2 ambient crystallized the film, decreased the leakage current density and resulted in reliable time-dependent dielectric breakdown characteristics. The conduction mechanism at low electric fields (<100 kV/cm) is due to Ohmic conduction; however, the Schottky mechanism becomes predominant at high fields (>100 kV/cm). Present studies demonstrate the use of Cu as a potential electrode material to replace the conventional precious metal electrodes for Ta 2O 5 storage capacitors. 相似文献
4.
We report the structural and optical properties of nanocrystalline thin films of vanadium oxide prepared via evaporation technique on amorphous glass substrates. The crystallinity of the films was studied using X-ray diffraction and surface morphology of the films was studied using scanning electron microscopy and atomic force microscopy. Deposition temperature was found to have a great impact on the optical and structural properties of these films. The films deposited at room temperature show homogeneous, uniform and smooth texture but were amorphous in nature. These films remain amorphous even after postannealing at 300 °C. On the other hand the films deposited at substrate temperature TS > 200 °C were well textured and c-axis oriented with good crystalline properties. Moreover colour of the films changes from pale yellow to light brown to black corresponding to deposition at room temperature, 300 °C and 500 °C respectively. The investigation revealed that nanocrystalline V 2O 5 films with preferred 001 orientation and with crystalline size of 17.67 nm can be grown with a layered structure onto amorphous glass substrates at temperature as low as 300 °C. The photograph of V 2O 5 films deposited at room temperature taken by scanning electron microscopy shows regular dot like features of nm size. 相似文献
5.
TeO 2 thin films were deposited on quartz substrates by rf reactive sputtering technique from a Te metal target. The obtained samples were annealed in an argon atmosphere at 450 °C for different annealing times up to 90 min. X-ray diffraction studies revealed that the as-grown samples were amorphous and there was no appreciable change in structure for a short annealing time. Thin films became polycrystalline with the tetragonal ( α-phase) structure of tellurium dioxide crystal with the increase of the thermal annealing time. The refractive index and optical energy gap of the films were calculated by modelling transmittance spectra. The optical energy gap decreased continuously from 3.83 eV to 3.71 eV with increasing thermal annealing time. 相似文献
6.
Aluminium oxide being environmentally stable and having high transmittance is an interesting material for optoelectronics devices. Aluminium oxide thin films have been successfully deposited by hot water oxidation of vacuum evaporated aluminium thin films. The surface morphology, surface roughness, optical transmission, band gap, refractive index and intrinsic stress of Al 2O 3 thin films were studied. The cost effective vapor chopping technique was used. It was observed that, optical transmittance of vapor chopped Al 2O 3 thin film showed higher transmittance than the nonchopped film. The optical band gap of vapor chopped thin film was higher than the nonchopped Al 2O 3, whereas surface roughness and refractive index were lower due to vapor chopping. 相似文献
7.
ZnO:Al network films were grown on nanochannel Al 2O 3 substrates at 300 K by direct current magnetron sputtering with an oblique target. The film thicknesses are 60 nm, 160 nm and 190 nm. The holes of the network films diminish with increasing film thickness. For the 60-nm thick film, the network is formed by connecting grains. For the 160-nm and 190-nm thick films, however, the network is formed by connecting granules. The granules consist of many small grains. All the network films have a wurtzite structure. The 60-nm and 160-nm thick network films mainly have a [1 0 1] orientation in the film growth direction while the 190-nm thick network film grows with a random crystallographic orientation. A temperature dependence of the resistance within 160–300 K reveals that the network films exhibit a semiconducting behavior and their carrier transport mechanism is thermally activated band conduction. Room temperature photoluminescence spectra for wavelengths between 300 nm and 700 nm reveal a violet emission centered at 405 nm for the 60-nm thick network film and a blue emission centered at 470 nm for both the 160-nm and the 190-nm thick network films. Annealing decreases the resistivity of the network film. 相似文献
8.
Indium tin oxide (ITO) thin films were deposited on quartz substrates by direct current magnetron sputtering and annealed in N 2 and air. The normal incidence transmittance of the films was measured by a spectrophotometer. The electrical parameters such as carrier concentration, mobility and resistivity were investigated by van der Pauw method. An optical model has been proposed to simulate the optical constants and thicknesses of the films from transmittance data, which combines the Forouhi-Bloomer model and modified Drude model. The relaxation energy in the Drude term is taken as energy-dependent for a better fitting in the visible spectral range. The simulated transmittance is in good agreement with the measured spectrum in the whole measurement wavelength range. The electrical parameters obtained from the optical simulation are well consistent with those measured electrically by van der Pauw method. The experimental results also indicate that the different post-deposition annealing treatments yield the distinct optical and electrical properties of ITO films. 相似文献
9.
CdO doped (doping concentration 0, 1, 3 and 16 wt%) ZnO nanostructured thin films are grown on quartz substrate by pulsed laser deposition and the films are annealed at temperature 500 °C. The structural, morphological and optical properties of the annealed films are systematically studied using grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), Micro-Raman spectra, UV–vis spectroscopy, photoluminescence spectra and open aperture z-scan. 1 wt% CdO doped ZnO films are annealed at different temperatures viz., 300, 400, 500, 600, 700 and 800 °C and the structural and optical properties of these films are also investigated. The XRD patterns suggest a hexagonal wurtzite structure for the films. The crystallite size, lattice constants, stress and lattice strain in the films are calculated. The presence of high-frequency E2 mode and the longitudinal optical A1 (LO) modes in the Raman spectra confirms the hexagonal wurtzite structure for the films. The presence of CdO in the doped films is confirmed from the EDX spectrum. SEM and AFM micrographs show that the films are uniform and the crystallites are in the nano-dimension. AFM picture suggests a porous network structure for 3% CdO doped film. The porosity and refractive indices of the films are calculated from the transmittance and reflectance spectra. Optical band gap energy is found to decrease in the CdO doped films as the CdO doping concentration increases. The PL spectra show emissions corresponding to the near band edge (NBE) ultra violet emission and deep level emission in the visible region. The 16CdZnO film shows an intense deep green PL emission. Non-linear optical measurements using the z-scan technique indicate that the saturable absorption (SA) behavior exhibited by undoped ZnO under green light excitation (532 nm) can be changed to reverse saturable absorption (RSA) with CdO doping. From numerical simulations the saturation intensity ( Is) and the effective two-photon absorption coefficient ( β) are calculated for the undoped and CdO doped ZnO films. 相似文献
10.
Gallium oxide (Ga 2O 3) films were deposited on MgO (100) substrates by metalorganic vapor phase epitaxy. Structure analyses showed that the films deposited at 550-700 °C were epitaxial β-Ga 2O 3 films with an out of plane relationship of β-Ga 2O 3(100)||MgO(100). The film deposited at 650 °C showed the best crystallinity and the microstructure of the film was investigated by high resolution transmission electron microscopy. A theoretical model of the growth mechanism was proposed and the in-plane epitaxial relationship was given to be β-Ga 2O 3[001]||MgO<011>. A four-domain structure inside the epitaxial film was clarified. The β-Ga 2O 3 film deposited at 650 °C showed an absolute average transmittance of 95.9% in the ultraviolet and visible range, which had an optical band gap of 4.87 eV. 相似文献
11.
A comparative characterization of C 60 thin films grown on silicon substrate by Physical Vapor Deposition and polymerized by chemical reaction with 1,8-octanediamine vapor or UV Pulsed laser irradiation has been carried out by means of Atomic Force Microscopy, and optical reflectance, transmittance and photoluminescence spectroscopies. The photovoltaic response and electrical characteristics of Au/C 60/Si diode structures have been investigated. The greatest photoluminescence efficiency and light transmittance, and at the same time the least photocurrent of diode structure were observed for chemically polymerized C 60. Found differences in morphology, optical, photoelectric and electrical properties of C 60 films polymerized by two methods indicate a difference in their composition. 相似文献
12.
Y 2O 3 thin films were in-situ deposited by ion beam sputtering on Si substrate. The influence of the deposition parameters are studied by X-ray diffraction, electrical measurements and high resolution transmission electron microscopy observations. The stress sate of the oxide layers is investigated by the sin 2ψ method as a function of the deposition parameters and the post-annealing treatments. Oxygen ion beam assisted deposition process or post-annealing of as-deposited thin films lead to the same relaxation of the internal compressive stress within the oxide layer. An SiO 2 layer sandwiched between Si and Y 2O 3 is always observed and should play a role both in the growing process and electrical properties of the MOS structure based on Y 2O 3 oxide layer. The results are interpreted in terms of diffusional process in the oxide, which are directly related to the temperature and the oxygen partial pressure during the growth process. 相似文献
13.
Scandium oxide (Sc 2O 3) films were deposited by electron beam evaporation with substrate temperatures varying from 50 to 350 °C. X-ray diffraction, scanning electron microscopy, spectrometer, and optical profilograph were employed to investigate the structural and optical properties of the films. The refractive index and extinction coefficient were calculated from the transmittance and reflectance spectra, and then the energy band gaps were deduced and discussed. Laser induced damage threshold of the films were also characterized. Optical and structural properties of Sc 2O 3 films were found to be sensitive to substrate temperature. 相似文献
14.
High-quality and well-reproducible PbSnS 3 thin films have been prepared by a simple and inexpensive chemical-bath deposition method from an aqueous medium, using thioacetamide as a sulphide ion source. X-ray diffraction analysis of the deposited films revealed that the as-deposited films were amorphous, however, an amorphous-to-crystalline phase transition was observed as the result of thermal annealing at 425 K for 1 h. The X-ray structure analysis of the collected powder from the bath annealed at 425 K for 1.5 h revealed an orthorhombic phase. Analysis of the optical absorption data of crystalline PbSnS3 films revealed that both direct and indirect optical transitions exist in the photon energy range 1.24–2.48 eV with optical band gaps of 1.68 and 1.42 eV, respectively. However, a forbidden direct optical transition with a band gap value of 1.038 eV dominates at low energy (<1.24 eV). The refractive index changes from 3.38 to 2.16 in the range 500–1300 nm. The high frequency dielectric constant and the carrier concentration to the effective mass ratio calculated from the refractive index analysis were found to be 4.79 and 2.3×1020 cm−3, respectively. The temperature dependence of the electrical resistivity of the deposited films follows the semiconductor behaviour with extrinsic and intrinsic conduction. The determined activation energies range are 0.35–0.42 and 0.76–85 eV, respectively. 相似文献
15.
Ge x Sb 40−x Se 60 ( x = 0, 2.42 and 23.41 at.%) thin chalcogenide films were deposited on glass and quartz substrates by the conventional thermal evaporation technique at 300 K. The chemical composition of the bulk material and as-deposited films were determined by energy dispersive analysis X-ray spectrometry (EDAX). X-ray diffraction pattern (XRD) of Ge x Sb 40−x Se 60 ( x = 0, 2.42 and 23.41 at.%) thin films indicates that they have amorphous structure. The optical transmission and reflection spectra were measured in the range of 500 to 2500 nm. The optical absorption coefficient spectra were studied for deposited samples. It is observed that the optical absorption edge shift to higher energy range, as the germanium content, x, increases in the film. The type of electronic transition, responsible for the optical properties, is indirect allowed transition. It is found that the optical band gap increases as the Ge content increases.The average coordination number ( Nc) in Ge x Sb 40−x Se 60 films increases, but the number of chalcogenide atoms remains constant. The number of Ge - Se bonds and the average bond energy of the system increase with the increase of the average coordination number. The optical band gap, Eg, increases with the increase of the average coordination number, ( Nc). Also the energy gap, E04, is discussed in terms of its relation to the chemical composition. The dispersion of the refractive index ( n) is discussed in terms of the Single Oscillator Model (SOM) (Wimple - Didomenico model). The single oscillator energy ( E0), the dispersion energy ( Ed) and the optical dielectric constant ( ?∞) are also estimated. 相似文献
16.
Thin films of SrCuO 2 with tetragonal structure have been epitaxially grown on SrTiO 3 (001) substrates by high-oxygen pressure sputtering technique. The interface structure between SrCuO 2 and SrTiO 3 and configuration of defects in SrCuO 2 thin films have been characterized by means of high-resolution transmission electron microscopy. Two types of film-substrate interface structure coexist and are determined as bulk-SrO-TiO 2-Sr(O) -CuO 2-Sr-bulk and bulk-SrO-TiO 2-SrO-Sr(O) -CuO 2-Sr-bulk. The planar faults with double SrO atomic layers in {100} planes in SrCuO 2 thin films are observed, which mainly arise from the coalescence of these two types of film-substrate interface structure. Meanwhile, planar faults in {110} planes are observed in thin films and structural models are proposed. 相似文献
17.
Thin (∼5.0 nm) Y 2O 3 films were deposited on n-type Si (1 0 0) substrate using RF magnetron sputtering. Detailed studies on the effects of post-deposition annealing (PDA) temperatures (400, 600, 800, and 1000 °C) in argon ambient on these films were performed by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), field emission scanning electron microscopy, and atomic force microscopy. Interfacial layer (IL) of SiO 2 in between Y 2O 3 and the Si substrate for sample annealed from 400 to 800 °C had been suggested from the results of FTIR. As for sample annealed at 1000 °C, presence of IL might consist of both Y 2Si 2O 7 and/or SiO 2 through the detection of Y 2Si 2O 7 compound and Si–O chemical bonding from XRD and FTIR analysis, respectively. For as-deposited sample, no detectable chemical functional group at the IL was recorded. Electrical characteristics of the Y 2O 3 films were acquired by fabricating metal-oxide–semiconductor capacitor as test structure. An improvement in the breakdown voltage ( VB) and leakage current density ( J) was perceived as the PDA temperature increased. Of the PDA samples, the attainment of the lowest effective oxide charge, interface trap density, total interface trap density, and the highest barrier height at 1000 °C had contributed to the acquisition of the highest VB and lowest J. 相似文献
18.
In the present work, we have deposited calcium doped zinc oxide thin films by magnetron sputtering technique using nanocrystalline particles elaborated by sol–gel method as a target material. In the first step, the nanoparticles were synthesized by sol–gel method using supercritical drying in ethyl alcohol. The structural properties studied by X-ray diffractometry indicates that Ca doped ZnO has a polycrystalline hexagonal wurzite structure with a grain size of about 30 nm. Transmission electron microscopy (TEM) measurements have shown that the synthesized CZO is a nanosized powder. Then, thin films were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature. The influence of RF sputtering power on structural, morphological, electrical, and optical properties were investigated. It has been found that all the films deposited were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (0 0 2) crystallographic direction. They have a typical columnar structure and a very smooth surface. The as-deposited films show a high transmittance in the visible range over 85% and low electrical resistivity at room temperature. 相似文献
19.
Bismuth titanate (Bi 4Ti 3O 12) thin films with a high c-axis orientation up to 99% were prepared on (100)-oriented silicon wafers by r.f. planar magnetron sputtering using a Bi 2TiO 5 ceramic target at a substrate temperature of 600 °C. From the Auger electron spectroscopy depth profile of the film, there is no evidence of interdiffusion of a specific element between the film and the substrate. Relative dielectric constant of these films depends on film thickness. The behavior was explained assuming a low-dielectric-constant interface layer. Using this assumption, the relative dielectric constant of Bi 4Ti 3O 12 film was estimated to be approximately 140. This value is close to that along the c axis in a bulk form. The remanent polarization and the coercive field were 0.8 μC cm −2 and 20 kV cm −1, respectively. 相似文献
20.
In this study, preparation of Nb-doped (0-20 mol% Nb) TiO 2 dip-coated thin films on glazed porcelain substrates via sol-gel process has been investigated. The effects of Nb on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Surface topography and surface chemical state of thin films was examined by atomic force microscope and X-ray photoelectron spectroscopy. XRD and Raman study showed that the Nb doping inhibited the grain growth. The photo-catalytic activity of the film was tested on degradation of methylene blue. Best photo-catalytic activity of Nb-doped TiO 2 thin films were measured in the TiO 2-1 mol% Nb sample. The average optical transmittance of about 47% in the visible range and the band gap of films became wider with increasing Nb doping concentration. The Nb 5+ dopant presented substitutional Ti 4+ into TiO 2 lattice. 相似文献
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