Assessing the growth window of stannous oxide by ion beam sputter deposition (IBSD)

SnOx films were fabricated on soda-lime glass and sapphire substrates by reactive ion beam sputter deposition (IBSD). A detailed growth series on c-plane sapphire was prepared using heater temperatures from room temperature to 600°C with different oxygen-to-argon ratios to investigate the impact of those parameters on thin film characteristics. By applying X-ray diffraction analysis and Raman spectroscopy an operating window was defined, in which SnO was grown without inclusions of parasitic Sn-related phases. The chemical bonding of the films was examined by X-ray photoelectron spectroscopy (XPS). Only a very narrow regime of oxygen flux was found with a composition close to stoichiometry. Furthermore, variation of the composition in SnO1±δ as well as the growth temperature were found to influence the morphology of the grown layer. The surface morphology was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). An average grain size of ≈10-50 nm was revealed for films grown at 200°C, which increases for annealed samples and samples grown at elevated temperatures. In addition to the expected influence on grain growth and surface roughness, disintegration of the SnO crystallites was found for inappropriate oxygen flux and heater temperature, giving way to incorporation of Sn or SnO2 species.