Interaction Mechanisms of Ammonia and Tin Oxide: A Combined Analysis Using Single Nanowire Devices and DFT Calculations

Tin oxide (SnO 2 ) represents a major fraction of research for developing solid-state gas sensors. Nevertheless, a detailed insight into the chemical-to-electrical transduction mechanisms between ammonia (NH 3 ) molecules and this metal oxide is still limited. Here, the adsorption of NH 3 on SnO 2 was examined by density functional theory (DFT) calculations and confronted to experimental data obtained with individual nanowire devices. It was concluded that under real working conditions nonlattice oxygens (O 5c ) adsorbed on SnO 2 exhibit a more basic character than lattice bridging oxygens (O 2c ), and consequently, they play a key role in the dehydrogenation of NH 3 on SnO 2, with N 2 and H 2 O as the main resulting products. The sensing process of ammonia on tin oxide nanowires not only involves physical mechanisms but also has a concomitant chemical nature that requires two molecules of NH 3 for the reaction to take place. Our theoretical modeling reveals why ammonia sensing is competitive to the adsorption of water molecules. As a result, interfering effects in monitoring traces of NH 3 intrinsically occur in humid conditions.