Thermo Optical Properties and Related Electronic Polarizabilities of MoO₃ Thin Films Using Ellipsometry

Abstract

Thermo optical properties are reported for thermally evaporated MoO₃ thin films using ellipsometry. The values of TOCs: dn/dT and dk/dT relating to MoO₃ thin films are found to be negative and positive, respectively over the temperature range 295-460 K and also are found to have the same trend over the range 120-300 K, and have values of the order of 10^-4 K^-1 and 10^-5 K^-1, respectively in the visible part of spectral range. The values of electronic polarizability were determined to be in the range from 8.2 to 8.21×10^-24 cm³ in the temperature range 120-460 K and over the same part of spectral range. Vacuum-heating and annealing in an oxygen plasma environment certainly assists in reducing a large amount of porosity in the films, but these series of actions yield irreversible changes in the morphology of the films. Once the films during oxidative-annealing turned into black in colour and new reduced chemical states were produced, then after that, original states of the films were very hard to restore. Ellipsometric data of MoO₃ thin films at or above the room temperature in the range 295-460 K seems to be controlled by first-order kinetics and could be interpreted in terms of polaronic excitations and hoppings. During the in-situ cooling runs, the changes in the ellipsometric data are interpreted in terms of bipolaronic excitations, but the possibility of simultaneous presence of polaronic and bipolaronic states cannot be ignored over the investigated temperature range.