Formation, negative capacitance and negative conductance effects in Selenium stacked layers sandwiched with Ag nanosheets

Abstract

In this work, we report the nature of formation in the presence and absence of Ag nanosheets being inserted between of two stacked layers of Se thin films which are grown onto Au substrates. The Se/Se and Se/Ag/Se films which are prepared by the thermal evaporation technique under vacuum pressure of 10(-5) mbar are studied by means of x-ray diffraction, conductance and capacitance spectroscopy techniques in the frequency domain of 0.01-1.80 GHz. Metal inducted crystallization processes from amorphous to hexagonal phases are achieved by using the Au substrate. The presence of Ag nanosheets of thicknesses of 50 nm between two 500 nm thick stacked layers of Se strongly affects the structural parameters through increasing the lattice constants, the microstrain and the defect density and decreasing the crystallite size. While the two stacked layers of Se sandwiched between Au and In metals displayed negative conductance effect associated with resonance in the capacitance and maximum microwave cutoff frequency (f(co)) of 0.68 GHz near 1.31 GHz, the insertion of Ag nanosheets forced the two stacked layers to exhibit higher positive conductance values and increased the f(co) values to 17.4 GHz. Ag nanosheets also caused negative capacitance (NC) effect in all the studied frequency domain. NC effect is associated with resonance-anti-resonance phenomena in the region of 1.33-1.37 GHz. The features of the selenium stacked layers make them attractive for use in microwave circuits as cavities, noise reducers, parasitic capacitance cancellers and bandpass filters.