Optical Properties of Annealed Tin(II) Oxide in Different Ambients

Tin(II) oxide powder is coated at room temperature onto transparent glass substrates by direct thermal evaporation. The films have high transparency (more than 80%) in the visible and near-infrared regions of the electromagnetic spectrum. In the region between 300 and 1300 nm interference fringes are sharp and well defined. The interference fringes are used to calculate the thickness of the amorphous as-prepared film (almost-equal-to 722 nm) and the refractive index is found to be 1.84 at 700 nm. The absorption coefficient of this film is almost-equal-to 6 x 10(3) cm-1 at 355 nm. The thickness of the film thus measured was compared with results obtained from the Tolansky method. The optical band gap calculated from the simple power law was found to be 3.3 eV. The films are annealed in either O2 or N2 atmosphere for 1 h at various temperatures between 250 and 400-degrees-C. It is found that the film is quite stable until about 400-degrees-C, beyond which the optical band gap reduces to 2.7 eV (in N2 atmosphere) and increases to 3.4 eV (in O2 atmosphere). At higher temperature the films annealed in nitrogen ambient do not show the interference fringes, whereas in the oxygen atmosphere the interference fringes are still observed.