Unique modulation effects on the performance of graphene-based ammonia sensors via ultrathin bimetallic Au/Pt layers and gate voltages.

Gas sensors with superior comprehensive performance at room temperature (RT) are always desired. Here, Au, Pt and Pt/Au-decorated graphene-based field effect transistor (FET) sensors for ammonia (denoted as Au/Gr, Pt/Gr and Pt/Au/Gr, respectively) are designed and fabricated. All these devices exhibited far better RT sensing performances for ammonia compared with graphene devices. Applying positive back gate voltages can further enhance their RT performance in which the Pt/Au/Gr devices show superior RT comprehensive performance such as a response of -16.2%, a recovery time of 4.6 min, and especially a much reduced response time of 54 s for 200 ppm NH with a detection limit of 103 ppb at a gate voltage of +60 V, and can be potentially tailored for further performance improvement by controlling the ratios of Pt and Au. The dependences of their performance on the gate voltage except for the response time could be reasonably explained by theoretical calculations in terms of the changes of the total density of states near the Fermi level, adsorption energies, transferred charges and adsorption distances. This study provides an effective solution for performance improvement of FET-based sensors synergistic effects of ultrathin-layer multiple-metallic decoration and gate voltage, which would promote the exploration of novel sensors.