Interaction of functionalized Ga2O3 NW-based room temperature gas sensors with different hydrocarbons

Ga2O3 nanowires (NWs) incorporated into capacitance-based room temperature gas sensors were functionalized with acetic and pyruvic acid (AC and PA, respectively) with the goal of achieving higher selectivity toward different groups of hydrocarbons. Fourier transform infrared spectroscopy (FTIR) was used to determine the geometry of the resulting adsorbate complexes. A bridge-like geometry was observed for adsorbed AC and a mixture of different geometries for PA, some of which had hydrogen-bonded OH groups. In addition, FTIR studies showed evidence of the enolic form of PA adsorbed on the surface. The AC-functionalized NWs showed a significant decrease in response to such common analytes as acetone and nitromethane as well as to triethylamine (TEA). In the case of PA-functionalized NWs, no response was observed to nitromethane, however, the response to TEA increased one order of magnitude compared to the bare NWs. FTIR spectroscopy was used to obtain more insight into the mechanism of interaction of AC- and PA-functionalized NWs with these analytes. This work demonstrates the use of a bifunctional molecule (PA) to modify the response of an oxide sensor in a way that a monofunctional molecule (AC) cannot. A significant result of this work is that the functionalization chemistry does not presume the existence of OH groups on the initial oxide surface.