Nonstoichiometric tin oxide films: study by X-ray diffraction, Raman scattering and electron paramagnetic resonance

Nonstoichiometric SnO/SnO2/SnO2-delta films were fabricated by DC magnetron sputtering and reactive DC magnetron sputtering of tin target with further 2-stage temperature annealing of synthesized materials. X-ray diffraction analysis, Raman spectroscopy and electron paramagnetic resonance (EPR) spectroscopy were employed to study the influence of oxygen content in the plasma during the sputtering process and the temperature of annealing on the stoichiometric and phase composition of synthesized films. It was found that the tin monoxide phase prevailed in the films fabricated by DC magnetron sputtering in the argon plasma followed by a 2-stage annealing process. Nanocrystalline films containing both tin monoxide and tin dioxide were synthesized when reactive magnetron sputtering with a small content of oxygen (of about 1 vol.%) was used. The increase of oxygen content in the plasma to the value of about 2 vol.% leads to the formation of amorphous films. The intensity of the Raman peaks inherent in SnO2 vibration modes was found to depend on the content of the tin monoxide phase in the films. This effect can be attributed to the dissipative transition of electronic excitation from tin monoxide to tin dioxide nanocrystallites.