Ellipsometric studies on cupric telluride thin films

The optical properties of cupric telluride (CuTe) thin films have been studied in the wavelength range 310-800 nm using spectroscopic ellipsometry (SE). Thin films of thickness between 30 and 150 nm were prepared by thermal evaporation at the rate of 15.6 Å/s on well cleaned glass substrates kept at 300 K under the vacuum better than 2×10⁻⁵ mbar. It has been found that the optical band gap increases with the thickness of the films. The refractive index of the films increases with the energy but the extinction coefficient first increases and then decreases gradually with energy. The analysis of the absorption coefficient determined from the extinction coefficient reveals that there is allowed direct transition with a band gap of about 1.5 eV. The increase in the band gap with the increase in the film thickness has been ascribed to defect levels in the band gap formed by defects in the films.     

Ellipsometric studies of N implanted Ti thin films

Spectroscopic ellipsometry was employed to study the optical response of N⁺ irradiated titanium thin films synthesized by pulsed laser deposition technique. The ellipsometric parameters were measured in the energy range of 1.5 to 5.5 eV. A combined Drude Lorentz (DL) model was employed to quantitatively describe the behavior of the dielectric response as a function of N⁺ irradiation fluence. A modeling based on effective medium approximation (EMA) was carried out to compute the volume fractions of Ti and TiN from the dielectric response functions. The plasma energy as computed from the DL model, decreased with increasing fluence. The results are explained on the basis of formation of TiN phase which was revealed from grazing incidence X-ray diffraction studies. This was further corroborated from the alterations on volume fraction of titanium as inferred from EMA based computation.     

Ellipsometric studies of microscopic surface roughness of CdS thin films

Analysis of changes in surface roughness of CdS thin films with preparation temperature was carried out using variable angle spectroscopic ellipsometry (VASE). The films studied were prepared by spray pyrolysis technique, in the substrate temperature range 200–360°C. The VASE measurements were carried out in the visible region below the band gap (E _g=2·4eV) of CdS so as to reduce absorption by the film. The thickness of the films was in the range 500–600 nm. Bruggeman’s effective medium theory was used for analysis of the surface roughness of the film. The roughness of the film had a high value (∼ 65 nm) for films prepared at low temperature (200°C) and decreased with increase in substrate temperature. This reached minimum value (∼ 27 nm) in the temperature range 280–300°C. Thereafter roughness increased slowly with temperature. The growth rate of the films was calculated for different temperature ranges. It was found that the deposition rate decreases with the increase in substrate temperature and have an optimum value at 300°C. Above this temperature deposition rate decreased sharply. The scanning electron micrograph (SEM) of the film also showed that the film prepared at 280–300°C had very smooth surface texture.     

Ellipsometric studies on ZnO:Al thin films: Refinement of dispersion theories

We characterize sputter-deposited aluminum-doped zinc oxide (ZnO:Al) thin films on glass and silicon substrates by variable-angle spectroscopic ellipsometry in the spectral range of 240 nm to 1700 nm. The model dielectric function includes the excitonic effects of direct band-gap semiconductors in the presence of high carrier densities as well as the scattering of free carriers by ionized donors. We show that an energy-dependent broadening term of the band-gap model avoids an extended absorption tail below the absorption threshold as it usually results from Lorentzian broadening. Uniaxial anisotropy takes account of the oriented growth of hexagonal crystalline ZnO:Al thin films. All the parameters derived from the optical measurements such as surface roughness, free-carrier concentration and mobility agree with the results of independent thin-film characterization methods such as atomic-force microscopy, Hall and four-point probe measurements. In the case of the glass samples, we need an additional interface layer which is confirmed by transmission-electron microscopy as an intermix layer of ZnO and glass.     

X-ray line broadening and photoelectrochemical studies on CdSe thin films

Cadmium Selenide (CdSe) thin films have been prepared on Indium doped tin oxide coated conducting glass (ITO) substrates at various deposition potential and solution pH values using potentiostatic cathodic electrodeposition technique. The deposited films are characterized using X-ray diffraction, scanning electron microscopy, energy dispersive analysis by X-rays, optical absorption, and photoelectrochemical techniques, respectively. X-ray diffraction pattern revealed that the deposited films are found to exhibit hexagonal structure 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 such as crystallite size, rms microstrain, dislocation density, and stacking fault probability. The variation of microstructural parameters with deposition potential, solution pH values, and annealing temperature are studied. Surface morphology and film composition are investigated by scanning electron microscopy and energy dispersive analysis by X-rays, respectively. Optical absorption analysis has been carried out to evaluate the optical parameters such as refractive index, extinction coefficient, real and imaginary dielectric constants, and packing density, respectively. Photoelectrochemical solar cells are constructed using as-deposited and annealed CdSe thin films as photocathode, and their power output characteristics are studied. The experimental observations are discussed in detail.     

Ellipsometric characterisation of thin films non-uniform in thickness

Ellipsometric formulae for thin films non-uniform in thickness are presented. A general type of thickness non-uniformity is considered and the influence of the varying angle of incidence is taken into account. The presented formulae are applied to the optical characterisation of polymer SiO₂-like thin films exhibiting a relatively strong thickness non-uniformity. It is shown that the complete optical characterisation of these polymer thin films can be performed. Thus, the spectral dependences of the optical constants, mean thickness and parameters related to the shape of thickness non-uniformity can be determined.     

Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

The epitaxial growth of ZnO thin films on Al₂O₃ (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10¹⁹ cm^− 3, 24.62 cm²V^− 1s^− 1, and 1.38 × 10^− 2 Ω cm, respectively.     

Effects of aluminium doping on zinc oxide transparent thin films grown by filtered vacuum arc deposition

Thin n-type ZnO films doped with different atomic concentrations of aluminium were grown by filtered vacuum arc deposition (FVAD) on glass substrates. The films were deposited using an oxygen working pressure of 2.0 mTorr with an arc current running at two 100 ms pulses s⁻¹. Structural, optical and electrical properties were investigated to understand the effect of Al doping on ZnO films. The best values were found for an ideal aluminium percentage between 4 and 6 at.%.     

X-ray fluorescent spectrometer with total X-ray reflection for studies of kinetics of thin film deposition

An X-ray fluorescent spectrometer with total X-ray reflection and minimum detection limit by zinc of n · 10⁻¹⁰ g is developed that allows performing analysis of elements from magnesium to uranium. This spectrometer is used to determine the elemental composition of Bi-Nd-Fe-O films grown on an Al₂O₃ single crystal (transparent sapphire, face 0001) in a gas-discharge sputtering chamber of a ceramic Bi_0.95Nd_0.05FeO₃ target. It is shown that the spectrometer allows registering formation and growth of films starting from the sputtering time of 15 s.     

Structural studies of ZnS thin films grown on GaAs by RF magnetron sputtering

X-ray diffraction (XRD) studies of ZnS thin films grown on GaAs (001) substrates at different temperatures by rf magnetron sputtering have been carried out using CuKα radiation. XRD analysis reveals that deposited films below 335 °C, assumed the zinc blend structure. Samples annealed at above 335 °C showed mixed phases of the zinc blend and wurzite structures. Information about crystallite size is obtained from (001), (111) and (104) diffraction peaks. The average crystallite size of the film was determined to be ∼ 32 nm using the Scherrer formula.     

X-ray photoelectron spectroscopic studies on pyrolysis of thin films of plasma-polymerized acrylonitrile

X-ray photoelectron spectroscopy is used to elucidate the chemical environments of the atoms in as-deposited plasma-polymerized acrylonitrile (PPAN) thin film and PPAN films pyrolysed at the temperatures 573 and 773 K. The photoelectron spectra are collected at the electron take-off angles of 20° and 70°. The C 1s, N 1s, and O 1s spectra of all the samples demonstrate clearly that the structural modifications take place owing to pyrolysis in the PPAN structure. Apart from the structural modifications, a decrease of nitrogen and an uptake of oxygen are evidenced. A few chemical species other than the usual ones are also detected.     

X射线反射(XRR)对薄膜样品厚度的研究

X射线的反射(XRR)测量法可精确地确定平行层及其薄膜结构,如测定光滑基体上聚合物膜的特性,包括层的厚度、密度和界面粗糙度.使用X'Pert X射线粉晶衍射仪对单晶硅片上的有机薄膜镀层进行了其厚度的精确测定,测定结果为该单晶硅片上的有机薄膜有3层,其厚度分别为5.0、60.2和245.3nm.并用倒易向量方法计算和验证了测量结果的正确性.还讨论了用X射线反射测定薄膜结构的一些影响因素.     

Electrical properties of thin oxidized aluminium films

Thin aluminium films of thickness 40 to 200 nm were deposited on to glass substrates at 573 K in a high vacuum. The deposition was carried out layer by layer and the interfaces between these layers were exposed to oxygen. The electrical resistivity was studied as a function of the film thickness, annealing time, annealing temperature and oxygen pressure. The temperature coefficient of resistivity and the activation energy for the conduction electrons were studied as a function of the film thickness and oxygen pressure. Fuchs-Sondheimer theory for electrical conduction was applied to the experimental results. The mean free path of the conduction electrons was calculated as a function of temperature and agreed well with the theoretical relation.     

Helium ion bombardment of thin aluminium films

A study is presented of the effect of 5 keV helium ion bombardment on thin (about 2000 Å) aluminium films using proton backscattering, scanning and transmission electron microscopy and α particle energy loss spectroscopy. Measurements of helium content after irradiation using proton backscattering indicate low below-saturation retention for both room temperature and low temperature implantations (19% and 24% respectively). Electron microscopy examination of the films reveals a severe deformation in the form of coarse and fine-scale wrinkling whose amplitude increases with increasing helium dose. This deformation does not appear to be the result of bubble swelling. An attempt has been made to quantify the wrinkling by measuring the energy loss spectrum of α particles transmitted through irradiated films and the combination of these measurements with a simple sinusoidal deformation model indicates an increase in film area of up to 20%.     

Energy-dispersive X-ray reflectivity and GID for real-time growth studies of pentacene thin films

We use energy-dispersive X-ray reflectivity and grazing incidence diffraction (GID) to follow the growth of the crystalline organic semiconductor pentacene on silicon oxide in-situ and in real-time. The technique allows for monitoring Bragg reflections and measuring X-ray growth oscillations with a time resolution of 1 min in a wide q-range in reciprocal space extending over 0.25-0.80 Å^− 1, i.e. sampling a large number of Fourier components simultaneously. A quantitative analysis of growth oscillations at several q-points yields the evolution of the surface roughness, showing a marked transition from layer-by-layer growth to strong roughening after four monolayers of pentacene have been deposited.     

On the specular reflectivity of rf sputtered AlSi alloy thin films

Surface features, roughness and reflectivity of AlSi alloy thin films deposited by rf sputtering at different voltages is studied for IC metallization.     

Microstructures of GaN thin films grown on graphene layers

Plan-view and cross-sectional transmission electron microscopy images show the microstructural properties of GaN thin films grown on graphene layers, including dislocation types and density, crystalline orientation and grain boundaries. The roles of ZnO nanowalls and GaN intermediate layers in the heteroepitaxial growth of GaN on graphene, revealed by cross-sectional transmission electron microscopy, are also discussed.