Structure and optical properties of thin titanium films deposited on different substrates

Thin films of titanium were deposited on different substrates at room temperature. Measurements were made of the optical constants and of the transmittance of titanium films evaporated on to fused quartz. Films of titanium 10 to 40 nm thick were found to have quite uniform transmittance throughout the visible spectrum. Because titanium getters strongly during its evaporation, pure and compact titanium films can only be produced by fast evaporation under extremely good vacuum conditions. All films prepared for optical measurements, for X-ray and for scanning electron microscopy studies were, therefore, deposited at a pressure 10^–4 Pa and with deposition rate 4 nm sec^–1. The measurements were made using a Beckman double-beam spectrophotometer UV 5230, Siemens D 500 X-ray diffractometer, and SEMCO nanolab 7 scanning electron microscopy.     

Structure and electrical properties of vacuum-deposited antimony telluride thin films on an amorphous substrate

Sb₂Te₃ thin films, 50–109 nm thick, have been prepared by vacuum evaporation on to quartz substrates. Electrical properties of as-deposited and annealed films show that the activation energy is thickness dependent. Optical measurements indicate that there is an indirect transition having an energy of 1.9 eV. Transmission electron micrographs show the fine grains of the deposit.     

Microstructure and optical properties of GaN films on sapphire substrates

Transmission electron microscopy (TEM), double crystal X-ray diffraction (XRD), photoluminescence (PL) and Raman scattering measurement were applied to study the correlation between the microstructure and material properties of the GaN films grown by light radiation heating metalorganic chemical vapor deposition (LRH-MOCVD), using GaN buffer layer on sapphire substrates. Corresponding to the density of the threading dislocation (TD) increasing approximately one order, the yellow luminescence (YL) intensity was strengthened from negligible to two orders higher than the band-edge emission intensity. The full width of half maximum (FWHM) of GaN (0002) peak of the XRD rocking curve was widened from 11 to 15 min, and in Raman spectra, the width of E₂ mode is broadened from 5 cm⁻¹ to 7 cm⁻¹. A ‘zippers’ structure of GaN buffer layer was discovered by high-resolution electron microscope (HREM).     

Optical and physical properties of vacuum-deposited PbS films

We describe the film density, void volume, thickness, species, reflectivity and crystal size of vacuum-deposited PbS films. Film densities, as determined from film thickness and areal film density measurements, were approximately one-half that of bulk PbS, resulting in a calculated average film void volume of about 60%. Film thicknesses ranging from 160 to 890 nm measured with the stylus and interferometer measuring methods were accurately determined for PbS films overlaid with approximately 100 nm of aluminum. The ion backscattering measuring method yielded an average [S]/[Pb] ratio of 0.955±0.07 or 1.00 (within experimental errors). The specular reflectivity of the glass-film interface of prism substrates, measured at an angle of incidence of 45° and at λ = 1060 nm, decreased as deposition time increased. The PbS films exhibited two sizes of crystals with the smaller located near the glass-film interface. The stylus, interferometer and ion backscattering measuring methods are useful in determining the density, void volume, thickness and species of vacuum-deposited films.     

Dielectric properties of vacuum-deposited bismuth oxide films

The dielectric properties of bismuth oxide films prepared by vacuum deposition have been studied in the frequency range 0.1–10 kHz and the temperature range 90–298.5 K. The capacitances C_p and C_s and the loss factor show dependences on the frequency, temperature and aging of the samples. The loss factor exhibits a flat maximum in its temperature variation curve at about 170 K. Interfacial polarization, which is caused by the excess bismuth and by various defects and impurities, is thought to be the main relaxation mechanism operating in the low frequency region.     

Asymmetries in the optical properties of vacuum-deposited organic films illuminated at the substrate and non-substrate surfaces

Tetracene, pentacene and nickel phthalocyanine films were prepared by vacuum deposition onto glass substrates. Their reflection spectra on illumination of the substrate (S) and the non-substrate (NS) surfaces were measured as a function of the sample thickness d. The reflectivity R and band shape of the spectra change with d and differ when measured from the S surface and the NS surface. These changes and asymmetries are interpreted as due to four factors: (i) the difference in surface roughnness, (ii) the difference in the refraction index at the film-air interface (NS) and the film-glass interface (S), (iii) the presence of stresses in the films and (iv) the Rayleigh-type scattering of light enhanced by the contact medium.A detailed analysis indicates the first and second factors to be dominant. Previous data for asymmetries in photoconductivity and photovoltaic effects can be consistently explained in terms of roughness-induced differentiation in the energy and spatial distributions of the structural defects in the near-surface layers of such films.     

Electrical and optical properties of annealed gallium arsenide thin films on glass substrates

The effects of annealing in vacuum on the electrical and optical properties of GaAs thin films deposited by the flash evaporation method were studied. Thin films of compound GaAs deposited upon glass substrates at room temperature were annealed in a vacuum of 2×10^–6 torr at different temperatures up to 350° C. The properties of the films depended strongly on annealing temperature. The lowest resistivity measured was about 1.6 × 10⁴ cm at an annealing temperature of about 240° C. The activation energy of as-deposited and annealed films were measured and compared. Optical absorption measurements of the asdeposited samples and the samples annealed at a temperature of 240° C were made as a function of photon energy.     

Structure and optical properties of evaporated films of vanadium

In the present work, the interpretation of the structure, nucleation and growth of Vanadium films will be studied. Film structure was inferred from transmission electron diffraction and microscopy of vanadium films evaporated simultaneously onto freshly cleaved rocksalt and carbon substrate. The investigated films were from about 10 to 80 nm thick, and the rate of the deposition was fixed at 3 nm sec-' throughout this work. The optical constants were determined for vanadium from transmission measurements on vacuum-evaporated polycrystalline thin films at room temperature in the infrared range. Transmission measurements were made on films in the thickness range 100 to 150 nm.     

Structure and optical properties of CuGaSe2 thin films

The structure and optical properties of vacuum-deposited films of CuGaSe₂ were studied at various substrate temperatures. Stoichiometric films could be obtained at substrate temperatures as low as 450 K. Epitaxial growth was observed on single-crystal NaCl substrates at temperatures above 500 K. The optical transition energies obtained at 1.68, 1.78 and 1.92 eV were in good agreement with previous results.     

Influence of substrates on the structural and optical properties of chemically deposited CdS films

Cadmium sulfide (CdS) films were chemically deposited on glass, polycarbonate (PC), polyethylene terephthalate (PET), and Si wafer. Effects of substrate types on the structural and optical properties of the films were investigated. There is a preferential orientation of the crystallites in the film grown on the glass along the c-axis (perpendicular to the plane of the substrate) producing a strong hexagonal (0 0 2) or cubic (1 1 1) peak, regardless of the presence of ITO coating. However, such preferential orientation decreases or disappears when the deposition was made onto PC or PET substrates. The crystallinity of CdS films on glass and Si is better than that of the other ones. The average transmittance of the films on PC and PET is about 50% and 55%, respectively, and increases up to 70% for glass substrate. The improvement of the transmittance was obtained from ITO-coated substrates.     

Structural, electrical and optical properties of Ga-doped ZnO films on cyclo-olefin polymer substrates

Ga-doped ZnO (GZO) films with a thickness of 100 nm were prepared on cyclo-olefin polymer (COP) and glass substrates at various temperatures below 100 °C by ion plating with direct-current arc discharge. The dependences of the characteristics of GZO films on the substrate temperature Ts were investigated. All the polycrystalline GZO films, which exhibited a high average visible transmittance of greater than 86%, were crystallized with a wurtzite structure oriented along the c-axis. The lowest resistivities of the GZO films were 5.3 × 10^− 4 Ωcm on the glass substrate and 5.9 × 10^− 4 Ωcm on the COP substrate.     

不同衬底上溅射TiO2薄膜的光学性能研究

在硅片和石英上利用射频溅射法沉积了TiO2薄膜,并分别在空气中进行了退火处理。利用椭偏光谱仪对硅片上薄膜进行了椭偏测试,利用紫外-可见分光光度计对石英上薄膜进行了透射光谱测试。利用解谱软件对椭偏谱和透射谱进行了建模解谱,获得了不同基片上薄膜在不同退火温度下的折射指数和消光系数,发现和TiO2块材的光学常数也有明显的区别。通过计算得到了系列薄膜的光学带隙,带隙值范围从3.35～3.88eV,可以为薄膜态TiO2体系的光学应用、设计和相关理论研究提供一定的依据。     

Structure of vacuum-deposited thick films of NiCrAl

Vacuum-deposited thick films for resistors of low sheet resistance cannot be investigated by electron optical techniques because of their thickness. For the X-ray investigation of the structure of NiCrAl films it was necessary to produce very thick films by vapour deposition in a step-by-step manner. These films were deposited at a substrate temperature of 250 °C and subsequently tempered under a high vacuum for 30 min at 300, 400, 500 and 700 °C. It was found that these very thick as-deposited films are amorphous while reflections of the phases Ni₃Al, NiAl and chromium became visible with increasing annealing temperature.Thus the structure of these thick films corresponds to that found by electron optical techniques for thin films of the same composition.     

D.C. electrical properties of vacuum-deposited CdTe films

The current-voltage characteristics of vacuum-deposited CdTe films were studied as a function of film thickness (2500–13000 Å) at various temperatures (0–110°C). The d.c. conduction mechanism was explained using a modified Poole-Frenkel equation.     

Structural and optical properties of GaN films grown on GaAs substrates by molecular beam epitaxy

GaN films are grown on [0 0 1] GaAs substrates by plasma-assisted molecular beam epitaxy using a three-step process that consists of a substrate nitridation, deposition of a low-temperature buffer layer, and a high-temperature overgrowth. X-ray diffraction and transmission electron microscopy indicate that this method promotes prismatic growth of c-oriented α-GaN. Photoluminescence studies show that the emission from cubic β-GaN inclusions dominates the spectrum.     

Properties of vacuum-deposited polyimide films

Vacuum-deposited polyimide (PI) thin films have been prepared by co-deposition of precursor pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) followed by thermal treatment. The dependency of the optical and electrical properties, chemical resistivity and mechanical stability on the composition (ODA:PMDA) and the degree of imidization of the PI layers have been investigated and discussed. The experimental results have yielded possibilities to microstructure the vacuum-deposited PI films by excimer laser irradiation or reactive ion etching in gas mixture CF₄/O₂.     

Related structural,electrical and photoelectrical properties of vacuum-deposited GaP thin films

GaP thin films with thicknesses from 0.1 to 0.6 μm were prepared by the thermal evaporation of the compound GaP onto quartz substrates at temperatures from ambient temperature to 740 °C. The properties of the films depended strongly on substrate temperature and deposition rate. With increasing substrate temperature the film structure changed from amorphous to textured polycrystalline with a strong [100] texture. The temperature of the amorphous-to-crystalline transition depended on deposition rate and was found to be 360 and 400 °C for deposition rates of 2 and 10 Å s^-1 respectively. At these temperatures the electrical resistivity of the films fell sharply from 10⁸ Ω cm to a minimum value of $\text{5 × 10}{}^4\text{Ω}\text{cm}$, after which it increased again with increasing temperature. The amorphous films exhibited a moderate photosensitivity with a maximum value near the temperature of the structural transition; above this temperature the films lost their photosensitivity completely. The spectral dependence of the photoconductivity was measured and an attempt was made to interpret the observed spectra.