Characterization of polycrystalline SnO2 films deposited by DC sputtering technique with potential for technological applications

Polycrystalline SnO2 films with different thicknesses were successfully deposited on glass substrate at room temperature using a DC sputtering technique. As-grown films showed the formation of an amorphous SnO2 phase, whereas the thermal annealed samples showed the formation of a SnO2 rutile-type structure. The structural study showed that the crystallinity of the annealed films was improved as a function of film thickness. Scanning electron microscopy images of the annealed films unveiled the formation of cracked surfaces along with columnar growth, irrespective of the depositon time. Raman spectroscopy measurements evidenced the presence of modes related to a surface disorder,a progressive strain reduction and a crystallinity improvement. UV-vis data analysis indicates a reduction in the band gap energy with films thickness due to presence of strain states as confirmed by theoretical calcuations. It was observed that the strained states in the films affected the sensing response to a methane gas flow with a better sensitivity for the thinner film.