Characterization of Arsenic doped MOS: powders رسالة ماجستير

Abstract

In this work, molybdenum sulfide powders ire doped with arsenic by the solid state reaction technique. The doped powders are characterized by the X-ray diffraction, electron nil py, energy dispersive X-ray spectroscopy, impedance

spectroscopy and current-voltage characteristics techniques. Various doping contents in

accordance with the formula MoAsS. The weight ratio (x) of arsenic in the samples is varied in the range of 0.00 — 0.80. The doped samples were then sintered at 200 °C for 20 hours in the air atmosphere. It is observed that the larger the arsenic content in the samples the smaller tbe crystallite sizes, the larger the microstrain, the larger the defect density and the larger the stacking faults percenlages. As Sintering the samples at 200 °C did not alter the trend of variation of the structural parameters. In addition, the increase in the As content in the MoS: powders is observed to increase the pores. Accumulation of As grains started appearing on (he surface of the samples as x exceeds 0.40%. On the other hand, the electrical measurement has shown that the electrical resistivity increases with increasing As content in the samples. The temperature dependent electrical resistivity measurements has shown that the activation energy (Ea) of free charge carriers in regions where thermionic emission is dominant increased. On the other hand, in regions where variable ranges hopping dominates the degree of electronic siate disorder and the variable range hopping distance increased while the density of localized states near Ferri levels decreased with increasing arsenic content. Moreover, the impedance spectroscopy studies have shown that the doped and wndoped MoS: samples can exhibit negative conductance effect. Negative conductance effect which is engineered by As content is beneficial for fabrication of microwave

devices useful in communication technology.