Optical properties of amorphous (As0.33S0.67)100−xTex (x = 0, 1, 5 and 10) chalcogenide thin films,photodoped step-by-step with silver

We have analysed in detail the effect of silver-content on the optical properties of Ag-photodoped amorphous (As_0.33S_0.67)_100?xTe_x (with x = 0, 1, 5 and 10 at.%) chalcogenide thin films; the chalcogenide host layers were prepared by vacuum thermal evaporation. Films of composition Ag_y[(As_0.33S_0.67)_100?xTe_x]_100?y, with y ? 18 at.%, were successfully obtained by successively photodissolving about 20- or 40-nm-thick layers of silver. The optical constants (n, k) have been accurately determined by an improved envelope method [J.M. González-Leal, R. Prieto-Alcón, J.A. Angel, D.A. Minkov, E. Márquez, Appl. Opt. 41 (2002) 7300], based on the two envelope curves of the optical-transmission spectrum, obtained at normal incidence. The dispersion of the refractive index of the Ag-photodoped chalcogenide films is analysed in terms of the Wemple–DiDomenico single-effective-oscillator model: $n^2(?\omega )=1-E_{\text{o}}{E}_{\text{d}}/(E_{\text{o}}^2-(?\omega {)}^2)$, where E_o is the single-oscillator energy, and E_d the dispersion energy. We found that the refractive index of the Ag-doped samples strongly increases with the Ag-content, whereas the optical band gap, $E_{\text{g}}^{\text{opt}}$, decreases also notably. For instance, in the particular case of x = 10 at.%, the largest Te-content, $E_{\text{g}}^{\text{opt}}$ decreases from 2.17 down to 1.67 eV. It should also be mentioned that, in the case of the undoped samples, when the Te-concentration increases from zero up to 10 at.%, the value of $E_{\text{g}}^{\text{opt}}$ decreases from 2.49 down to 2.17 eV.     

Optical properties and structure of amorphous films Agx(As0.33S0.67−ySey)100−x

As₃₃S_67−ySe_y, where y = 0, 16.75, 33.5, 50.25 and 67, amorphous thin films were prepared by a vacuum thermal evaporation technique. The films with known silver concentrations and good optical quality were prepared by thermal vacuum evaporation of a silver film on the top of As₃₃S_100−ySe_y films with sequential step-by-step optically- and thermally-induced diffusion and dissolution (OIDD) of silver. The range of silver content was x = 0–25 at.%. The kinetics of OIDD of silver were measured optically by monitoring the change of thickness of the undoped part of the chalcogenide during broadband illumination. Compositions of the reaction products have been determined by scanning electron microscope with energy-dispersive X-ray microanalyser EDS. Optical properties $(T\text{,}n\text{,}{E}_{\text{g}}^{\text{opt}})$ of thin films were measured and/or calculated by the Swanepoel method [R. Swanepoel, J. Phys. E: Sci. Instrum. 16 (1983) 1214]. The refractive index increase with increasing silver and selenium concentration has been shown. The difference of the refractive index (Δn) between undoped and silver doped films was ∼0.4 and between As₃₃S₆₇ and As₃₃Se₆₇ was films ∼0.42. Non-linear indices of refraction were estimated according to Tichy’s formula [H. Ticha, L. Tichy, J. Optoel, Adv. Mat. 4 (2002) 381]. The values of non-linear refractive index grew with increasing silver and selenium content. The difference of optical bandgap, $\mathrm{\Delta }{E}_{\text{g}}^{\text{opt}}$, between undoped As₃₃S₆₇ and fully doped films with Ag and Se was ∼1 eV. Raman spectroscopy showed a decrease in S–S or Se–Se bonds with increasing silver content.     

Correlations between apparent activation energy and thermostability and glass forming ability for Fe based metallic glasses

Apparent activation energies (E_g) of glass transition, glass transition temperature (T_g) and crystallization temperature (T_x) of amorphous alloys of composition Fe_91?xB_xZr₅Nb₄ (FBZN, 5 ? x ? 30 at.%) and Fe_61?xCo_xZr₅B₃₀Nb₄ (FCZBN, 0 ? x ? 15 at.%) were obtained by using differential scanning calorimeter (DSC) measurement and Kissinger equation, and correlations between E_g and T_g, T_x and glass-forming ability (GFA) were studied in the present work. It was found that the T_g and T_x are not independent each other for each glass composition in the two alloy systems, but related by a formula, T_x = αT_g+β, where α and β are constants, and were measured by nonisothermally scanning in the DSC together with the Lasocka’s equation. The E_g was found to be directly proportional to α and β, respectively, and had a correlation with T_x and T_g, $T_{\text{x}}=\frac{E_{\text{g}}-1.09}{3.527}{T}_{\text{g}}-\frac{E_{\text{g}}-4.86}{0.0041}$, indicating that E_g determines linear relationship between T_x and T_g. Supercooled liquid region ΔT_x is used as characterization of GFA of the Fe based metallic glasses and related to E_g and T_g by a formula: $\mathrm{\Delta }{T}_{\text{x}}=E_{\text{g}}(\frac{T_{\text{g}}}{3.527}-234.9)+1185.37-1.309T_{\text{g}}$, indicating that E_g and T_g can characterize GFA of the Fe based metallic glass well.