Sub-ppb-Level Detection of Nitrogen Dioxide Based on High-Quality Black Phosphorus

The development of gas sensors based on two-dimensional (2D) layered materials has received lots of focus attributing to their excellent gas sensitivity. Here, a black phosphorus (BP) gas sensor device is fabricated based on high-quality few-layered BP microribbons using a facile route. Although BP is well known to oxidize in ambient conditions, energy dispersive spectroscopy (EDS) mapping manifests that the few-layered BP microribbons undergo slight oxidation and contamination during the grinding process. It is interesting that the surface and side of BP microribbons have nanoscale thin films and step-like nanoscale thin films, respectively, owing to the in-plane slip of the few-layered BP microribbons in the process of grinding, which are different from the conventional BP bulk crystals. The layered BP microribbon gas sensor demonstrated a high response to low-concentration NO2 and a very low limit of detection (LOD) of 0.4 ppb of NO2 under N2 and air conditions, which is the lowest LOD for NO2 detection reported so far. The mechanisms for excellently sensitive detection of NO2 for the BP microribbons have been investigated by first-principles calculations combined with experiment results, revealing that the sensitization mechanisms of the BP microribbon sensor are abundant nanoscale thin films, an optimum bandgap range with optimal carrier concentration, a hierarchical homojunction structure, and strong adsorption energy to NO2. In addition, the BP microribbon sensor demonstrated high selectivity to NO2, a low LOD under a high relative humidity, and good repeatability. The reported results of the BP sensor may provide great promise for improving the performance of other 2D material-based gas sensors and may expand sensing applications.