PVD grown SnS thin films onto different substrate surfaces

Recent interests focus on tin mono sulphide as a potential candidate for an absorber layer in heterojunction solar cells. In the present investigation, SnS thin films have been deposited onto different substrates such as glass, ITO and Mo-coated glass substrate by thermal evaporation method. The compositional, microstructural and photoelectrochemical properties of the SnS films were analyzed depending upon the chemical nature of the substrates used. The SnS layers were polycrystalline with Herzbergite orthorhombic structure on all three substrates and had nearly stoichiometric elemental composition with a Sn/S ratio of ~1.01. The films grown on ITO and Mo-coated glass substrates exhibit (040) as preferred orientation whereas the films deposited on glass showed (111) plane as predominant. The layers were densely packed and well adherent to the substrate surface. The Raman spectra showed bands at 64, 163, 189 and 219 cm^?1, which corresponds to the single phase (SnS) composition of films. p-type conductivity of all the deposited films were determined by the photoresponse studies. The highest photoresponse for the films on the ITO substrate indicates their appropriateness for the solar cell application.     

Temperature dependence of ZnO thin films grown on Si substrate

The structural and optical properties of ZnO thin films grown on Si substrates were investigated for different growth temperatures in the range of 520–720 °C. X-ray diffraction investigations revealed the preferred c-axis oriented growth of ZnO thin films, which was further confirmed by the presence of ZnO (0002) diffraction spots with arc shape. The increase in growth temperature transformed surface morphology from pyramidal with columnar grains to relatively flat surface with increased grain size. In addition, the increased growth temperature caused redshift and intensity enhancement of band-edge emission of the ZnO, which were related to the increase in tensile strain and the grain size, respectively.     

Relationships between mechanical behaviour and craze morphology in thin films of polystyrene

A new technique has been developed to study the relationship between mechanical properties and craze microstructure in thin films (1 to 5m) of polystyrene. Thin film samples of thicknesses in this range could be strained in a conventional testing machine and subsequently examined in the deformed state in an electron microscope. The strain rate was systematically varied and its effect was investigated on both quenched and annealed samples. Correlations were found between craze morphology and ductility. A new craze parameter has been defined as the width of a strip of material which is involved in the development of a craze. From this value, the average strain and the average volume fraction of fibrils within a craze can be calculated.     

The effect of substrate temperature on the physical properties of tantalum oxide thin films grown by reactive radio-frequency sputtering

Thin films of TaO_x were deposited on Si(1 0 0) by radio-frequency magnetron sputtering at substrate temperatures of 25, 100, 200, 300, 400, and 500 °C. The properties of TaO_x thin films deposited with different oxygen-to-argon gas ratios and substrate temperatures were evaluated. The results show that the films with lowest leakage current density were obtained at ambient temperature with an oxygen mixture ratio (OMR) of 60% and the oxygen-to-tantalum ratio has a minimum with increasing deposition substrate temperature. From the current–voltage (I–V) characteristics of the TaO_x thin films as a function of deposition substrate temperature, we found that the leakage current density in the TaO_x thin films increases with increasing deposition substrate temperature. The higher leakage current density in the TaO_x films is correlated to the oxygen deficiency in TaO_x films and crystallization at higher deposition temperature.     

The influence of substrate morphology on the growth of thin silicon films: A GISAXS study

Thin Si films, with thickness between 100 and 300 nm, were deposited by PECVD (Plasma Enhanced Chemical Vapour Deposition) in silane gas (SiH₄) highly diluted by hydrogen. The degree of dilution and the discharge power were varied in order to obtain different crystalline to amorphous fractions in the films. Two types of substrates were used. The first one was amorphous and relatively flat while the second one was polycrystalline with a roughness of a few tens of nanometers. The crystal fraction in the deposited samples, as estimated by Raman spectroscopy, varied between 0 and 40%, and the individual crystal size was between 2 and 8 nm. The larger individual crystals are usually present in those samples with the highest crystal fraction. The sample density, estimated upon the spectral distribution of the dielectric function in the infra red, was 15-25% less than the density of crystalline silicon. The GISAXS pattern of all of the examined samples indicated the presence of not-spherical-like “particles” in the “bulk” of the thin films, with an average “particle” size between 1.5 and 4 nm. These “particles” are most probably voids and their shape indicates columnar growth. By applying the GISAXS technique on samples deposited on different substrates, the borderline deposition conditions between “transport limited growth” and “growth dominantly influenced by plasma surface reactions” was estimated.     

Investigation of LiNbO3 thin films grown on Si substrate using magnetron sputter

A RF magnetron sputter system was used to deposit lithium niobate (LiNbO₃) thin films on (1 1 1)-oriented Si substrates. An optimal sputtering condition with RF power of 100 W, Ar/O₂ ratio of 1 and substrate temperature of 575 °C was investigated. The smallest surface roughness of 6.0 nm for the deposited LiNbO₃ was measured using atomic force microscopy. The crystallinity was examined by low angle X-ray diffractometer. Using the SOPRA GES5 spectroscopic ellipsometer, the associated refractive index and extinction coefficient as a function of wavelength were measured. High optical performance with crystallinity structure of the deposited LiNbO₃ thin films was demonstrated.     

A comparison of the morphology of crazes formed in thin films and in bulk specimens of polystyrene

The microstructure of crazes formed in solvent-cast thin films have been studied by transmission electron microscopy. The results have been compared with the microstructure of crazes determined from the examination of replicas obtained from the fracture surfaces of bulk specimens. The structure of crazes formed in thin films and in the bulk have been shown to be similar with the exception that much finer fibril structures are observed in thin films at large deformations. A model of the microstructure of a craze is presented.     

Switching in polystyrene and polymethyl methacrylate thin films: effect of preparation conditions of the polymers

Switching without any break in the electrodes was observed in polystyrene and polymethyl methacrylate films by controlling the current using a high resistance connected in series with the sample. The effect of the method of polymerization on the switching characteristics were studies for both polymers. Polymers were prepared by -ray irradiation or by catalytic or noncatalytic thermal polymerization. The switching characteristics gave poor reproducibility for the catalytically polymerized polystyrene, but no difference was observed for the three types of polymethyl methacrylate from different origins. In the case of polystyrene, the lower the molecule weight, the higher was the threshold voltage. With polymethyl methacrylate such a dependence was not observed. In both polymers the on-state is relatively stable. When the samples in the on-state were heated above 100° C, they were converted to the offstate. No dots or breaks on the sample were detected by scanning electron microscopy (SEM) after switching has occurred.     

Effects of substrate material and annealing temperature on morphology of zinc oxide films

Abstract

A two stage chemical deposition (TSCD) technique is used to produce ZnO films on quartz glass (QG), soda lime glass (SLG) and high purity alumina (HPA) from an aqueous solution of zinc complex. The effects of the substrate material on the chemical composition and morphology of the deposited layer are investigated. The effects of different annealing temperatures (180, 300, 500 and 800°C) on the morphology and orientation of the ZnO crystallites are also determined. X-ray diffraction diffractograms show that above 300°C, the intensity of (002) peak considerably decreases with increasing temperature. Results indicate that changing the substrate from QG to SLG does not significantly influence the chemical composition of the deposited layer. These variations can be attributed to different factors including (a) physorption of cold complex solution, (b) growth behaviour of the nuclei forming on the substrate and (c) the surface energy of the substrate. Owing to the existence of the morphological differences bound to the molecular nature of the substrate, properties of the coatings are found not to be the same. HPA substrate causes clustering of the ZnO crystallites, while QG and SLG substrates do not distinguishably show this effect. Observations show that clustering is intensified by annealing at temperatures > 180°C.     

Development of crystallinity and morphology in hafnium dioxide thin films grown by atomic layer epitaxy

The structural development of HfO₂ thin films grown from HfCl₄ and water onto glass substrates by atomic layer epitaxy at 500 °C was studied with X-ray diffraction, atomic force microscopy and scanning electron microscopy. The films were found to contain two regions of different crystallinity: a thin amorphous starting layer and a subsequent preferentially oriented polycrystalline layer. The films were built up of densely packed grains. Substantial surface roughening occurred along with increasing film thickness. The films were chlorine free as analyzed by Rutherford backscattering spectrometry.     

The effect of growth parameters on CrN thin films grown by molecular beam epitaxy

In this paper, we report on the controlling of the effect of growth parameters such as substrate temperature and the ratio of Cr and N atoms on phase formation, surface morphology and crystallization of CrN(001) thin films grown by plasma-assisted molecular beam epitaxy on the MgO(001) substrate. The reflection high energy electron diffraction, atomic force microscopy, X-ray diffraction and scanning tunneling microscopy are used to characterize the thin films grown under various conditions. High-quality CrN(001) thin films are achieved at a substrate temperature 430 °C with a low Cr deposition rate.     

Optical characterization of organic material bromoindium phthalocyanine thin films grown by electron beam evaporation

This paper presents the optical properties of organic material bromoindium phthalocyanine (BrInPc) thin films grown by electron beam evaporation technique. The paper describes the optical characteristics of BrInPc thin films, which have been determined using spectrophotometric measurements of the absorbance, transmittance and reflectance at normal incident of light in the spectral range 300–1,100 nm. The optical band gap energy and type of the electronic transition have been determined by analysis of spectral behavior of absorption coefficient, which reveals the probability of both direct and indirect transitions. Other optical constants, such as refractive index, extinction coefficient, complex dielectric constant and optical conductivity of thin films have been evaluated. Moreover, the width of band tails of localized states (Urbach energy), steepness parameter and width of the defect states have been determined by studying the absorption coefficient spectra just below the fundamental absorption edge.     

Structure and microstructure of EB-PVD yttria thin films grown on Si (111) substrate

Structure and microstructure of yttria thin films grown by electron beam physical vapour deposition on a stationary Si (111) substrate at room temperature (RT), 500° and 700 °C, were investigated by the grazing-incidence X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy provided information on the surface contamination from the atmosphere and the Y oxidation state. A strong effect of the deposition temperature and the vapour flux incidence angle was found. The film deposited at RT is polycrystalline with very fine grains of the body-centered cubic (bcc) crystallographic symmetry. An increase of deposition temperature results in a rapid growth of bcc grains with an improved crystalline structure. Moreover, the based-centered monoclinic phase appears for the deposition temperature of 700 °C. Preferred grain orientation (texture) with two main components, (400) and (622), was observed in the films deposited at 500 °C whereas no texture was found for 700 °C. The microstructure exhibits the columnar feather-like structure of different degrees of perfection which can be explained by the shadowing effects caused by an oblique vapour flux incidence angle. Surface morphology of the films is governed by a combination of the triangular and four-sided (square) columns. All films were found to be dense with a little porosity between the columns.     

Anomalous variation of resistance in bismuth thin films and the effect of substrate temperature

Bismuth thin films of thickness 720 Å have been vacuum deposited at various substrate temperatures on glass substrates and their resistances are recorded as a function of temperature after annealing the films at 200°C. The resistance (R) versus temperature (t) curves show anomalous behaviour, in that the resistance first decreases as the temperature increases and then increases as the temperature increases, thus showing a minimum in resistance, R_min at a temperature t_min. The position of R_min (i.e. t_min) and the magnitude of R_min vary with substrate temperature. However, no such anomalous behaviour is observed for the film deposited at room temperature and its resistance monotonically decreases with increase in temperature. These observations have been explained by considering that the bismuth films behave as narrow band gap semiconductors because of the quantum size effect and by the facts that in polycrystalline films the electronic mean free path will be limited by the grain size and also that the average grain size of the film increases as the substrate temperature during deposition increases.     

The effect of substrate morphology on the diameter distribution of carbon nanotubes grown on silica and ceramic substrates

Large-scale well-aligned carbon nanotube film and carbon nanotube bundles have been fabricated on smooth silica and rough polycrystalline ceramic substrates by pyrolysis of ferrocene/melamine mixtures. The images of transmission electron microscopy (TEM) and scanning electron microscope (SEM) show that carbon nanotubes grown on the silica substrate have uniform outer diameters of about ∼ 25 nm and lengths of about 40 μm, while those on the ceramic substrate have outer diameters from 10 to 90 nm and lengths up to 100 μm. Electron energy-loss spectroscopy (EELS) spectra show that nanotubes grown on the two different substrates are pure carbon tubes. The effects of substrate micro-morphologies on the diameters of carbon nanotubes have been discussed.     

The substrate effect on Ge doped GaN thin films coated by thermionic vacuum arc

This study focuses on characterization and understanding of the substrate effect on Ge doped GaN thin films coated onto transparent substrates. The produced films were deposited onto unheated glass and unheated polyethylene terephthalate by using thermionic vacuum arc technique. Gallium nitride and germanium pellets were used in the thin film production. Reflectance, refractive index and thicknesses of Ge doped GaN thin films were measured by optical interferometer using Cauchy model for fitting. The transmittances were determined in the wavelength range between 200 and 1000 nm by using UV–Vis double beam spectrophotometer. The optical Tauc method was used to determine the band gap energies of produced thin films. Surface morphologies of produced thin films were characterized by atomic force microscopy and also field emission scanning electron microscopy. In conclusion, the substrate effect on the optical and morphological properties of the produced thin films was observed.