We demonstrate that conductometric gas sensing at room temperature with SnO2 nanowires is enhanced by visible and supra bandgap UV irradiation when and only when the metal oxide nanowires are decorated with Ag nanoparticles (r < 20 nm); no enhancement is observed for the bare SnO2 case. We combine spectroscopic techniques with conductometric gas sensing to study the wavelength dependency of the sensors response, showing a strict correlation between the Ag loaded SnO2 optical absorption and its gas response as a function of irradiation wavelength. Our results lead to the hypothesis that the enhanced gas response under UV-vis light is the effect of plasmonic hot electrons populating the Ag nanoparticles surface. Finally we discuss the chemoresistive properties of Ag loaded SnO2 sensor in parallel with the theory of Plasmon-Driven Catalysis, to propose an interpretative framework that is coherent with the established paradigma of these two actually separated fields of study.
SnO<sub>2</sub> and ZnO and metal oxide nanowires were synthesized by vapor transport process in a horizontal tube furnace. The
peculiar characteristic of these materials is the emission of visible photoluminescence (PL) when they are excited with
UV light. The visible photoluminescence of tin and zinc oxide nanowires is quenched by nitrogen dioxide at ppm level in
a fast (time scale order of seconds) and reversible way. Besides, the response seems highly selective toward humidity
and other polluting species, such as CO and NH<sub>3</sub>. We believe that adsorbed gaseous species that create surface states can
quench PL by creating competitive nonradiative paths.
The work function of nano Porous Silicon (PS) has been studied by the kelvin probe method as a function of the exposure to different gaseous species. Characterisation has been performed n dark and in presence of sub band and supra band gap light Surface Photovoltage (SPV)measurements. Traces of ammonia and nitrogen dioxide change drastically the shape of SPV as a function of photon energy:light induces transitions from and to surface states produced by gas adsorption. The results foresee the possibility to improve semiconductor sensor selectivity by using monochromatic light at well defined frequency able to activate/deactivate surface states where species are adsorbed
The work function of tin oxide has been studied by the kelvin probe method as a function of the exposure to different gaseous species. Characterisation has been performed in dark and in presence of sub band and supra band gap light (Surface Photovoltage measurements). The light changes the response towards gases in particular at room temperature. The results foresee the possibility to improve semiconductor sensor selectivity by using monochromatic light at well defined frequency able to activate/deactivate surface states where species are adsorbed.
Films of (alpha) -Fe<SUB>2</SUB>O<SUB>3</SUB>, whose high non-linear optical susceptibility (chi) <SUP>(3</SUP>) has been recently reported, have been prepared by the sol-gel method using two different sol-gel syntheses, both starting from inorganic salts as precursors, Fe(NO<SUB>3</SUB>)<SUB>3</SUB>-9H<SUB>2</SUB>O or FeCl<SUB>3</SUB>- 6H<SUB>2</SUB>O. Thermal treatments on films obtained by dip coating lead to the (alpha) -Fe<SUB>2</SUB>O<SUB>3</SUB> hematite structure for both preparations as indicated by XRD, Raman and X-Ray Absorption Spectroscopy measurements.