F. Abd El-Salam

Optical properties of Sb2Se3 thin films

Abstract The optical constants (the refractive index n and the absorption index k) of Sb2Se3 thin films deposited at room temperature on quartz have been calculated in the wavelength range (5000–2000 nm) using a transmission spectrum. Both n and k were found to be practically independent on either time, up to 6 months, or the film thickness in the range of 102–760 nm. Beyond the absorption edge, the absorption is due to allowed indirect and direct transitions with energy gaps of 1.225 and 1.91 eV, respectively. The value of the optical gap depends on the annealing temperature. X-ray analysis showed that the prepared films at room temperature had amorphous structure while the films annealed at 200°C for 1 h were verified to be crystalline.

Aging Characteristics of Rapidly Solidified Al–20 wt% Zn Alloy

Al-20 wt% Zn samples were obtained at room temperature by rapid cooling from the melt. The quenched samples were aged at different temperatures below and above the transformation temperature (503 K) for 2 h, then quenched to room temperature. Structure variations and changes in internal friction, thermal diffusivity, Youngs modulus and resistivity were traced for these testing conditions. The different results were explained in terms of the thermally induced structures in the alloy.

Switching phenomenon in amorphous Sb2Se3

Abstract The switching phenomenon in amorphous Sb 2 Se 3 films was found to be a memory switch. The OFF-state was found to have three forms for the voltage and current relation. The threshold voltage (switching voltage) showed thickness and temperature dependence and increased with increasing thickness and/or decreasing temperature. The ratio of the activation energy at switching and the thermal conduction activation energy was 0.5, and the calculated values of the temperature inside the active region at the moment of switching make explanation of the memory type switching in Sb 2 Se 3 films possible on the basis of the electrothermal breakdown process.

The temperature dependence of the electrical resistivity of Al-Zn alloy thin films

Abstract The electrical resistivity of vacuum evaporated A1–40 wt. % Zn thin films was found to decrease as thickness increased, thus exhibiting a size effect. Isothermal annealing of the quenched samples started with an anomalous resistivity increase to maxima followed by a normal decrease to limiting values. In the Guinier-Preston zone temperature range a measurable difference in resistivity was affected by the annealing temperature which is not the case of the bulk material. The role played by the quenched-in vacancies, grain boundary migration, phonons and the state of the solute atoms were used to explain the observed resistivity variations which were found to consist with the expected state of the alloy at the different testing temperatures. The irregularities of the position and magnitude of the observed maxima were explained in terms of the attenuation of the incident electron wave within the film as a multiple scattering effect. The observed anomalies in the resistivity during annealing were attributed to phase transformation and atomic ordering.

Temperature and thickness dependence of photoconductivity and density-of-states distribution for Bi doped Ge20S80

Abstract Differential thermal analysis data showed that the addition of 5 at% Bi to Ge 20 S 80 caused T g and T c to shift towards higher temperatures but had no significant influence on the structural units responsible for the formation of the glass network. Bi addition and temperature both increased the electrical conductivity of Ge 20 S 80 . Dark electrical conductivity increased for Ge 20 S 75 Bi 5 films with decreasing thickness. Photoconductivity started with values higher than those of dark conductivities and both gradually decreased to saturation with time. For any thickness, increased duration of light soaking yielded temperature dependence of dark conductivity, characterized with decreasing conduction activation energies. The density of states (DOS) distribution obtained from light-induced effects on dark conductivity showed a peak around 0.4−0.47 eV below E c , which is the midgap. The results were explained on the basis of the additional localized states in the gap, the positive and negative defects centred at Bi and S, increased carrier mobilities with temperature, heterogeneous film structure and induced electron-hole traps.

Dependence of creep rate on grain diameter in Sn-0.5at.%Bi alloy

Abstract Variations in the creep properties of Sn-0.5at.%Bi alloy were studied by using samples of various grain diameters in the stress range 2.47–3.25 kgf mm−2. A decrease in the steady state creep rate and an increase in the activation volume were obtained with increasing grain diameter. This was interpreted by the adsorption of the solute atoms (bismuth) in the vicinity of the grain boundaries as well as on the moving dislocations because of the surface activity of the bismuth atoms with respect to the matrix (tin).

Electrical resistivity of crystalline Sb2Se3

Abstract Resistivity variations of bulk and crystallized Sb 2 Se 3 films of different thicknesses were studied at different temperatures. The dark electrical resistivity decreases with increasing film thickness. For substrate temperatures below the crystallization temperature, resistivity variations were characteristic of amorphous films and for greater temperatures an anomalous initial resistivity increase was observed. At higher working temperatures the transition region was not observed. Positive decreasing TCR values were obtained up to 340 K after which a negative constant value was attained for polycrystalline films. While the resistivity and the conduction activation energy decreased with increasing film thickness, the free charge carrier concentration increased and gave a value of the order 10 12 −10 16 cm −3 for the bulk material.

Structural variations in antimony selenide

Abstract DTA graphs, X-ray diffraction patterns and electron micrographs showed that bulk Sb2Se3 obtained by furnace cooling or quenching the melt from 1123 K to room temperature has a crystalline nature of orthorhombic structure while the prepared thin films with any thickness showed amorphous structure. The sharp endothermic peak at 603 K showing phase transition extended as a plateau to about 623 K with the quenched material depending on the degree of crystallinity. Crystallization of thin films was attained by annealing at 423 K in air and at 448 K under vacuum. This amorphous into crystalline transformation showed itself as an additional exothermic peak at 453 K in the DTA graph. Increasing the temperature and time of annealing and also the film thickness enhanced crystallization which was found to start with the preferred orientation on the planes (020), (120) and (130). The observed structural changes were explained in view of the variations of atomic energy and internal stresses, the nature of boundary angles, the chain and layer structure of Sb2Se3 and the role played by surface defects during crystallization.

Anomalous behaviour of transient creep in commercially pure aluminium

Transient creep of pure and commercial aluminium was studied under a constant stress of 18·6 MPa at different temperatures ranging from 613 to 698 K. The anomalous values of transient creep parametersβ, n ranging from 0·003–0·055 (±0·001) and 0·5–1·0 (±0·05) respectively, which were found in this temperature rangs, might bs ascribed to the superplastic behaviour of pure and commercial aluminium. The activation energy of transient creep for pure Al was found to be about (2·4 +0·07) × 10−22) kJ/atom. characterizing a dislocation glide-cross slipping mechanism.

The effect of precipitation on the optical properties of Al-Zn thin films

Abstract The optical constants n and k of Al-40 wt% Zn alloy thin films deposited at room temperature were calculated using a transmission spectrum in the wavelength range from 2.5 to 20 μm. The thickness of the films ranged from 10 to 85 nm. The investigated samples were aged at 373 K and 473 K for 1 h and some micro-characteristics of Al-Zn alloy films such as the free charge concentration N, the relaxation time τ, the static conductivity σ, the electron velocity at Fermi surface Vf and Fermi energy were determined. The effective absorption assumed the value 63.7% and the absorption due to bound electrons is therefore 36.3%. The role of the solute atoms (Zn) was considered to explain the results.