Effect of thermal annealing on the cathodoluminescence of evaporated CdS films

Cathodoluminescence (CL) of evaporated undoped CdS films was investigated before and after thermal annealing in air and in vacuum at 300 °C for several hours. Pure CdS single crystals were studied for comparison. CL spectra were obtained at room temperature using the electron microprobe technique. The two well-known (green and red) CL bands of pure CdS were observed for all samples. Annealing of the films in air decreased the green luminescence while vacuum annealing led to its increase. The red luminescence increased under both annealing conditions. The results were explained in terms of radiative transitions attributed mainly to native defects and their complexes. The role of oxygen and residual impurities on the CL of thin films was discussed. A modulation of the CL spectra was obtained in thin films owing to optical interference.     

Epitaxial growth and structure of CdS films evaporated onto Ge

CdS evaporated in vacuum grew epitaxially at all substrate temperatures from 300 to 500° C on (100), (110) and (111) surfaces of germanium. On (100) substrates the CdS grew with the sphalerite structure in parallel orientation to the substrate. Films grown throughout the epitaxial range of temperature gave diffraction patterns that contained no satellite spots. They all contained 111 streaking, however. The films were therefore free of threedimensional defects but contained a high density of {111} planar defects. On the (110) substrates the CdS grew with the sphalerite structure in parallel orientation for substrate temperatures below about 370° C and the diffraction patterns of these films were free of satellite spots but contained 111 streaks of low intensity. In the diffraction patterns of the films grown above about 370° C doubling of the spots appeared and a domain structure was observed in the micrographs. This was due to the occurrence of a domain-form phase transformation of the sphalerite structure. On the (111) substrates the CdS grew with the wurtzite structure in (0001) orientation. No satellite spots or streaks appeared in the diffraction patterns of these films. Moiré fringes were seen in the micrographs of both (100) and (111) substrate specimens.     

Cubic forms in the surface morphology of CdS evaporated films

CdS films were grown by vacuum evaporation onto muscovite mica substrates. The surface structure of the films was investigated by electron microscopy, electron diffraction and X-ray diffraction. Growth structures typical of cubic symmetry have been observed, and those of the wurtzite-sphalerite and sphalerite-wurtzite transitions are also described. A discussion of experimental results in terms of the nucleation mechanism is given.     

Characterization of evaporated gold-tin films

Evaporated Au and Sn films with total thicknesses in the range 1000–5000 Å were studied using backscattering of 2.0 MeV ⁴He ions, scanning and transmission electron microscopy and X-ray diffraction. Si and oxidized Si were used as substrates. In addition, some films were made self-supporting. The atomic percentage of Sn in the films ranged from about 30 to 90. Diffusion was observed within the unannealed films and resulted in the formation of the phases AuSn, AuSn₂ and AuSn₄. The backscattering spectra showed that the films form a layered structure before heat treatment. In most cases annealing for 10 min at about 200°C is sufficient to homogenize the films. The annealed films are made up of a single phase whenever this is consistent with the overall composition. Otherwise the annealed films contain a mixture of two of the Au phases or AuSn₄ and Sn depending on the atomic percentage of Sn in the films.     

Characterization of evaporated gold-indium films on semiconductors

Evaporated Au-In films with total thicknesses in the range 200–6000 Å have been studied by backscattering of 1.5 MeV He⁺ ions, SEM, X-ray diffraction and with the electron microprobe. Both Si and GaAs were used as substrates, and the atomic percentage of Au in the films was less than 30. A fast diffusion within the films was observed which resulted in the formation of the AuIn₂ phase at room temperature. The compositional structure and the annealing behaviour of the films have been studied in the temperature range 25°–600°C. A model for the annealing behaviour of the films is presented. The Au-In films have been used for ohmic contacts to GaAs and a correlation between the resistance of such contacts and the alloying behaviour is attempted.     

X-ray diffraction investigations on evaporated iron films

The structure of thin iron films of thickness about 1500 Å was studied by means of X-ray diffraction analysis. Evaporation and X-ray examination were carried out in the 10^?10 Torr range without exposing the films to the atmosphere using a recently developed ultrahigh vacuum diffraction chamber. The films were deposited onto glass substrates at a rate of 10 Å min^?1 at room temperature and were subsequently annealed at 320°C. They show a (110) fibre texture with a mean crystallite size of the (110)-oriented crystals that was distincly smaller than the film thickness. The lattice parameter was found to be always less than the corresponding value for a bulk iron standard, which can be ascribed to the formation of thermally induced strains.     

Assembly of CdS nanoparticles in patterned structures by a novel ion-entrapment process in thermally evaporated fatty acid films

The formation of cadmium sulfide nanoparticle assemblies in a patterned manner on suitable substrates is described. The protocol for realizing such structures comprises the following steps. In the first step, patterned films of a fatty acid are thermally evaporated onto solid supports using suitable masks (e.g., a transmission electron microscope grid). Thereafter, the fatty acid film is immersed in cadmium sulfate solution and Cd2+ ions entrapped in the lipid matrix by electrostatic complexation with the carboxylate ions of the fatty acid molecules. The final step involves reaction of the entrapped Cd2+ ions with Na2S, leading to the in situ generation of cadmium sulfide nanoparticles within the patterned lipid matrix. This approach shows promise for generating patterned nanoparticle assemblies of different chemical compositions.     

Mobility studies of evaporated tellurium films

The Hall mobilities of evaporated Te films with various grain sizes were measured as a function of temperature over the range 77–330 K and were compared with theoretical values based on lattice and ionized impurity scattering. A large deviation of the Hall mobility from the theoretical values was found in Te films with a small grain size and this deviation was attributed to grain boundary scattering. The linear correlation observed between the Hall mobility at room temperature and the average grain size supports this interpretation.     

Characterization of evaporated tellurium oxide films

The evaporation of tellurium dioxide was carried out by resistive heating and electron-beam evaporation, and the resulting films were subsequently characterized using X-ray diffraction, infrared absorption spectroscopy and electron diffraction techniques. The infrared results of these films showed a marked deviation from the initial stoichiometry, indicating decomposition of the compound. From X-ray and electron diffraction data, it was found that the films had Te₂O₅ stoichiometry. Electron-beam evaporated films showed single crystal growth on a sodium chloride substrate, while those films obtained by resistive heating were wholly amorphous. Furthermore, when fabricated into capacitors, these films showed high capacitance and high dielectric strength (4.6×10⁶V cm^–1) suitable for passive devices.     

Magnetic properties of evaporated CoCr films

Perpendicular magnetic CoCr films were prepared on glass substrates using electron beam evaporation. The magnetic properties depend strongly on the substrate temperature, Ts. The anisotropy field,H_{k}^{eff}, and the perpendicular coercivity, Hc(perp) show maximum values at Tsaround 250°C. In this case, the alignment of c-axis is optimal and the grain size is smallest. The lattice spacing of the c-planes increases wlth Tsuntil 300°C. When the films prepared below 200°C were annealed around 300°C in high vacuum, the saturation magnetization, Ms, increased. The value of Ms, however, decrease by annealing above 400°C. In spite of the decrease of Msdue to the annealing above 400°C,H_{k}^{eff}and Hc(perp) increase by annealing above 400°C. If the films were bombarded by argon ions during film growth, Msdecreased and the internal stress changed from tensile to compressive. For low substrate temperature (below 150°C),H_{k}^{eff}decreased due to ion bombardment.     

Structural investigations of evaporated GeSe films

Depending on the technological procedure of vacuum sublimation, amorphous or polycrystalline films of germanium monoselenide were obtained. The film composition determined by Auger electron spectroscopy at the surface and in the depth proved to be stoichiometric.     

Perpendicular anisotropy of evaporated magnetic films

Evidence of the existence of origins of perpendicular anisotropy other than the ordinary magnetostrictive effect is presented with a brief review of other studies. As one of these origins, the effect of the grain boundaries or the microscopic shape effect is discussed. The amount of perpendicular anisotropy observed in the stripped films does not seem capable of explanation by this effect only.     

Structural features of evaporated nickel films on oxide supports

Nickel was vacuum-deposited at high temperature (1000–1600°C) on alumina and at room temperature on Hiflosupercel (diatomaceous earth). Light microscopy/Scanning electron microscopy/Energy Dispersive x-ray analysis investigations on the coated materials indicate structural features such as uniform dispersal and firm binding of nickel crystallites on the oxide surfaces and suggests that the feasibility of vacuum technology may offer certain advantages over the conventional processes for making dispersed metal catalysts.     

Digital recording properties of evaporated cobalt films

Thin coatings of cobalt, cobalt-nickel, and cobalt-phosphorous have been in use for some years as a medium in recording drums. Recent papers [1]-[3] have described the recording properties of chemical- and electro-deposits on flexible plastic bases for in-contact digital tape recording. TheBHloop squareness and high coercivities achievable in films of a few microinches thickness makes them particularly suitable for high packing density storage. This paper describes the preparation and recording properties of vacuum-deposited cobalt films of varying thickness and coercivity. Comparisons made with oxide tapes show that a marked improvement in packing density is achievable. Correlations between pulse width and amplitude with thickness and magnetic properties throw some light on the mechanism of pulse recording.