Platinum single atoms on tin oxide ultrathin films for extremely sensitive gas detection

Abstract

Single atom Pt functionalized SnO₂ ultrathin films are synthesized by atomic layer deposition (ALD) for application as sensing layers in resistive gas sensors. Here it is shown that the electronic conductivity of the SnO₂ ultrathin films is very sensitive to the exposure to triethylamine (TEA), and that the thickness of the SnO₂ films (from 4 to 18 nm) has a crucial effect on the sensor response. The 9 nm thick SnO₂ film shows the best response to TEA, while a further decrease in the film thickness, i.e., 4 nm, leads to a very weak response due to the two orders of magnitude lower carrier concentration. Single atom Pt catalysts deposited on the 9 nm SnO₂ film result in an unexpectedly high enhancement in the sensor response and also a decrease of the sensor working temperature. Consequently, Pt/SnO₂ thin film sensors show the highest response of 136.2 to 10 ppm TEA at an optimal temperature of 200 °C (that of a pristine SnO₂ film sensor is 260 °C), which is improved by a factor of 9 compared to that of pristine SnO₂. Moreover, the Pt/SnO₂ sensor exhibits an ultrahigh sensitivity of 8.76 ppm⁻¹ and an extremely low limit of detection (LOD) of 7 ppb, which to our best knowledge are far superior to any previous report. Very fast response and recovery times (3/6 s) are also recorded, thus making our sensor platform highly suitable for highly-demanding applications. Mechanistic investigations reveal that the outstanding sensing performances originate from the synergistic combination of the optimized film thickness comparable to the Debye length of SnO₂ and the spillover activation of oxygen by single atom Pt catalysts, as well as the oxygen vacancies in the SnO₂ films.