Highly sensitive and rapidly responding room-temperature NH3 gas sensor that is based on exfoliated black phosphorus

Abstract

Black phosphorus (BP) has recently attracted significant interest in gas sensing because of its outstanding electronic and optical properties. In this paper, we demonstrated a series of gas sensors for detecting NH3 at room temperature that were based on BP nanosheets that were exfoliated for various durations. The BP nanosheet gas sensors showed excellent sensitivity for the detection of NH3 down to 100 ppb (~32%) under ambient conditions compared to previous reports. The BP nanosheets that were exfoliated for 60 min showed the highest response to 100 ppm NH3, namely, 121%, which was 2.5 times greater than the response of ground BP. The corresponding sensor also exhibited a relatively stable response in humidity between 22% RH and 35% RH. Moreover, the prepared NH3 gas sensor showed high selectivity, fast response and recovery, and excellent repeatability. According to various experimental and theoretical studies, the response and binding energy of BP towards NOx were higher than those towards NH3. However, very interestingly, the response of the exfoliated BP nanosheets to NH3 was higher than that to NOx in our work. The selectivity transformation from NOx to NH3 was mainly caused by the different layer spacing of the ground BP and the change in spacing between the BP nanosheet layers with different exfoliation times, increased oxygen incorporation, phosphate ions and defects that is induced by the liquid-phase exfoliation process, which led to the variations in its band gap and surface states.