In situ monitoring of heat assisted oxidation and its effects on the structural, dielectric and optical conductivity parameters of Pb thin films as promising terahertz transmitters

Abstract

In this work, thermal vacuum deposited lead thin films are subjected to an in situ monitoring of the oxidation process during heating in the temperature range of 300-480 K by the X-ray diffraction technique. The heating effects on the crystallinity, phase formation and structural parameters are additionally investigated with the help of computer simulation to explore the possible formed oxides. In addition, the heating effects of the optical transmission, reflection and absorption, optical conduction and terahertz signal transmission spectra are also investigated. It is found that, the cubic crystalline Pb films comprises tetragonal Pb3O4 in it’s as grown form. When heated, while the Pb3O4 content increases from 18.5% to 21.3%, tetragonal PbO phase with weight of 30.9% is formed. Even though more than half of the film content relates to the oxides after the samples were left to cool, the microstrain and defect density in the films decreased and the grain size increased. Optically, the oxidation process enhanced, the light transitivity, reflectivity and decreased the absorption coefficient. Two energy band gaps one is assigned to Pb3O4 with value of 2.12 eV before heating and the other is assigned to PbO with value of 2.60 eV after cooling are detected. Dielectrically, the oxidation increased the real part and the quality factor in the infrared region of light. On the other hand, the optical conductivity analyses which are treated via Drude-Lorentz approach has shown that Pb films exhibit plasmon frequency and mobility values of 3.2 GHz and 0.62 cm2/Vs, respectively. The oxidation slightly lowered the optical conductivity parameters. Application directed analysis of the terahertz cutoff frequency has shown that the oxidized Pb films behaves as promising layers for use as terahertz wave transmitters suitable for visible light communications.