Ar/O2 and H2O plasma surface modification of SnO2 nanomaterials to increase surface oxidation

Tin oxide operates widely as a gas sensor for a variety of molecules via a mechanism that relies on interactions with adsorbed oxygen. To enhance these interactions by increasing surface oxygen vacancies, commercial SnO2 nanoparticles and CVD-grown SnO2 nanowires were plasma modified by Ar/O2 and H2O plasmas. Scanning electron microscopy revealed changes in nanomaterial morphology between pre- and post-plasma treatment of H2O treated materials but not Ar/O2 treated materials. Powder X-ray diffraction patterns of the bulk SnO2 showed the Sn4+ is reduced by H2O and not Ar/O2 plasma treatments. X-ray photoelectron spectroscopy indicated Ar/O2 treatment results in increasing oxygen adsorption with increasing plasma power and treatment time, without changing Sn oxidation. With the lowest plasma powers and treatment times, however, H2O plasma treatment results in nearly complete bulk Sn reduction. Although both plasma systems increased oxygen adsorption over the untreated materials, there were clear differences in the tin and oxygen as well as morphological variations upon plasma treatment.