Effect of annealing temperature on the morphology, structure, and optical properties of nanostructured SnO(x) films

Nanostructured SnO(x) films were obtained by molecular beam epitaxy (MBE). The morphology, structure, and optical properties of obtained films annealed in the temperature range of 200 degrees C-1000 degrees C were studied. The reflection high-energy electron diffraction during the film deposition by the MBE method and the x-ray phase analysis showed that the initial films are in the polycrystalline phase. A single orthorhombic SnO2 phase was obtained for the first time after annealing the SnO(x) film in the air at a temperature of about 500 degrees C. The sharp change in the optical constants near the temperature of 500 degrees C was established using ellipsometry. The pronounced absorption edge appears in the short-wave region at temperatures above 500 degrees C and it disappears at lower temperatures. The film thickness changed non-monotonically during the annealing in the air. At first, it grows from 45 nm to 65 nm (active oxidation to 500 degrees C), and then (above 600 degrees C) it begins to decrease. The annealing at temperatures of 500 degrees C-1000 degrees C leads to the film compaction, since the film thickness decreases to 50 nm, but the refractive index increases by 10%-15%. Optical constants track the progress of film phase and morphological changes.