Thermal evolution of the morphology, structure, and optical properties of multilayer nanoperiodic systems produced by the vacuum evaporation of SiO and SiO2

The alternate vacuum evaporation of SiO and SiO₂ from separate sources is used to produce amorphous a-SiO _x /SiO₂ multilayer nanoperiodic structures with periods of 5–10 nm and a number of layers of up to 64. The effect of annealing at temperatures T _a = 500–1100°C on the structural and optical properties of the nanostructures is studied. The results of transmission electron microscopy of the samples annealed at 1100°C indicate the annealing-induced formation of vertically ordered quasiperiodic arrays of Si nanocrystals, whose dimensions are comparable to the a-SiO _x -layer thickness in the initial nanostructures. The nanostructures annealed at 1100°C exhibit size-dependent photoluminescence in the wavelength range 750–830 nm corresponding to Si nanocrystals. The data on infrared absorption and Raman scattering show that the thermal evolution of structural and phase state of the SiO _x layers with increasing annealing temperature proceeds through the formation of amorphous Si nanoinclusions with the subsequent formation and growth of Si nanocrystals.     

Influence of Output Optical Losses on the Dynamic Characteristics of 1.55-μm Wafer-Fused Vertical-Cavity Surface-Emitting Lasers

Semiconductors - The results of studying the dynamic characteristics of 1.55-μm single-mode vertical-cavity surface-emitting lasers (VCSELs) formed by the fusion of wafers of high-quality...     

Velocity profile in ultraviscous-liquid flow in the screw channels of extrusion machines

A method of solving the flow problem for a nonlinear ultraviscous liquid in a screw channel in the Stokes approximation is outlined, together with the results.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 61, No. 3, pp. 392–398, September, 1991.     

Experimental evidence of Snoek-like relaxation in annealed metallic glass

The frequency dependence of the internal friction (IF) of annealed Co-based metallic glass (MG) has been measured at elevated temperatures in the frequency range of 10⁻³≤f≤10³ Hz. It has been found that the IF increases with frequency decrease at a constant temperature. To explain this observation, an analytical model of IF due to anelastic relaxation in a symmetrical two-well potential has been proposed. The model shows that the IF rise with decreasing frequency observed in the experiment can be interpreted as a high frequency tail of a Snoek-like relaxation with distributed activation energies in deep relaxation centers of annealed glassy structure.