A.H. Ammar

The relationship between optical gap and chemical composition in SbxSe1−x system

Abstract The optical constants of vacuum deposited SbxSe1−x amorphous thin films (x = 0.075, 0.15 and 0.20 at%) of different thicknesses (90–150 nm) were studied in the wavelength range 550–800 nm. It was found that both the refractive index n and the absorption index k are independent of the film thickness, whilst there is a distinct dependence of n and k on the Sb content. The allowed optical transition was found to be non-direct, the corresponding optical gaps Egopt are determined. The width of the band tail Ee is also determined. As a result, Egopt decreases while Ee increases with increasing Sb contents. The variation of Egopt with x for SbxSe1−x agree with the optical gap Eo predicted theoretically in terms of random bond network proposed by Shimakawa. The relationship between the optical gap and chemical composition in SbxSe1−x amorphous system is discussed in terms of the average heat of atomization Hs and the average coordination number m. The results of these calculations can be used to rationalize the observed optical properties of these materials.

Optical and other physical characteristics of amorphous Ge–Se–Ag alloys

Abstract Measurements of optical properties and differential thermal analysis have been made on alloyed samples of Ge and Se with Ag, prepared under vacuum to evaluate their glass-forming tendencies. Optical absorption measurements showed that the fundamental absorption edge is a function of composition. The optical absorption is due to direct transition and the energy gap increases with the increase of Ag content. The average heat of atomization and related parameters such as the average coordination number N co , the number of constraints per atom, N con , were also calculated. It was found that there is a correlation between the glass-forming ability and the number of lone-pair electrons L . An attempt has been made to evaluate the correlation according to the Liang criterion. Our experimental results support this criterion.

The optical properties of manganese thin films

Abstract The optical constants n and k of thin manganese films of different thicknesses ranging from 20 up to 50 nm were determined in the spectral range 3.5–20 μm. The results were compared with the predictions of the Drude free electron theory and anomalous skin effect theory. The previous theories were used to evaluate some micro characteristics of Mn thin films such as the free charge concentration N , the relaxation time τ, the static conductivity σ s , and the electron velocity at Fermi surface V F and the value of the effective area of Fermi surface A F . Using the optical constants, the optical conductivity ( σ = σ 1 + i σ 2 ) was also estimated. It was found that the contribution of the effective absorption A eff equals 69%, i.e. the absorption due to bound electrons may be 31%.

Electrical transport properties of manganese thin films

Abstract Thin manganese films of thicknesses in the range 20–160 nm have been vacuum deposited on glass substrates at room temperature. The electrical resistivity, Hall coefficient and thermolelectric power were measured. The electrical resistivity data were analyzed using Chambers and Fuchs theories to determine the resistivity of manganese films of infinite thickness ϱ0, the mean free path of the electrons l0 and the specularity parameter P. The electrical resistivity as a function of the film temperature was used to determined the temperature coefficient of resistivity. The Hall coefficient measurements at room temperature was used to calculate the number of the free electron (n which was used in conjunction with the reduced Fermi energy η obtained from thermoelectric power measurements to calculate the effective mass of the electron m ∗ in manganese films. As found, ϱ = 312.5 μΩ cm , l 0 = 281.46 nm , P = 0.209, n = 3.87 × 10 28 m −3 , η = 378.3 and m ∗ = 0.014m 0 .

Study of nonisothermal crystallization in amorphous Se90In9.3Cu0.7 alloy

Amorphous alloy of Se90In9.3Cu0.7 has been prepared by the usual melt-quench technique under vacuum. Data from differential thermal analysis (DTA) at various heating rates and x-ray analysis of this alloy were investigated and reported. The activation energies of glass transition, Eg, and crystallization transition, Ec, were evaluated from the dependence of the glass temperature Tg and the crystallization temperature Tc on the heating rate. The crystalline phases resulting from DTA were identified using x-ray diffraction. The results reveal that the prepared alloy is structurally heterogeneous at a molecular level, in which In6Se7, Cu5Se4, and Cu2Se dispersed in Se–Se matrix.