Zahia Hadjoub

The aim of this article is to investigate the effect of dielectric loss tangent on frequency dispersion of output reactance and capacitance in GaAs MESFETs. For this purpose, measurements of output impedance modulus and phase have been carried out within a frequency range of 10 Hz to 10 kHz, and various voltage values of gate-source (V _gs = 0, −0.2, −0.3, −0.35, −0.4, −0.45, −0.5 and −0.6 V) and drain-source (V _ds = 0.7, 0.9, 1, 1.5 and 2 V) Based on the concept of complex permittivity of semiconductor material, complex capacitance is used to analyze and simulate frequency dispersion of output reactance and capacitance of GaAs MESFETs. The results show that conductor losses which dominate the dielectric loss tangent are attributed to trapping mechanisms at the interface of devices; so they influence the frequency dispersion of output reactance and capacitance in particular at low frequencies. This reveals that frequency dispersion of these parameters is also related to dielectric loss tangent of semiconductor materials which affects the response of electronic devices according to frequency variation.

Acoustic microscopes can be used to measure Rayleigh and longitudinal wave velocities in a specimen at microscopic resolution. These velocities are deduced from the analysis of the so-called acoustic signatures or V(z) curves. Such curves are obtained by recording the output signal, V, as the specimen is defocused along the z axis of the lens. In this context, we investigate Co-Additives effects on reflectance functions, R(θ) and acoustic signatures. The elastic properties of Lithium cobalt mixed ferrites of different compositions from the experimentally and simulation observed that the values of longitudinal wave velocities vary from 5072 m/s to 6833 m/s whereas transverse velocities from 3084 m/s to 4105 m/s. The variation of the elastic moduli with composition was interpreted in terms of the binding forces between the atoms.

Recent interest in investigations of mechanical, elastic, electronic, optical and transport properties of the silicon carbide/silica (SiC/SiO