Morphological and optical properties of tin oxide nanomaterial thin film deposited using vacuum evaporation

Abstract

A 250 nm thick pure tin film was deposited on quartz substrates by vacuum evaporation of 99.9% pure tin metal. The films were heated in a two-step annealing sequence for 3 h at 200 and 3 h at 400 °C with an electric furnace to decrease their surface roughness. This process transformed the films into tin(II) oxide. Subsequently, the films were annealed at five temperatures for 3 h each: 600, 700, 800, 900 and 1000 °C. The crystal structure of the film on the quartz substrate was completely transformed into SnO₂ at 600 °C. With the increase of annealing temperature to 1000 °C, the size of the lattices appeared to decrease on the thin film. In addition, the annealing process led to the formation of pores on the surface, but the number of pores and the lattices volume decreased with increased annealing temperature. The optical properties of the thin film were characterized by the use of visible spectrophotometry which showed a high refractive index at around 2.08–2.27. Interestingly, the SnO₂ thin film with the highest refractive index at 2.27, which was obtained at 1000 °C, exhibited the lowest Urbach energy. Therefore, the SnO₂ thin film has a high potential for optical applications, especially in dielectric waveguides and solar cells.