Two-Dimensional Boron–Phosphorus Monolayer for Reversible NO₂ Gas Sensing

We proposed a boron–phosphorus monolayer (BP-ML) and investigated its gas sensing properties by density functional theory including the van der Waals dispersion correction term. Electronic property analysis reveals that BP-ML is a semiconductor with an indirect bandgap of 0.54 eV. The adsorption energy calculations of nitrogen-containing gases (NCGs) such as N2O, NO2, NH3, and NO show that these gases are physisorbed on the BP-ML surface. Among the studied NCGs, the NO2 molecule exhibits a relatively higher charge (0.43 e), which further confirms a robust charge transfer and more reactivity with the BP-ML surface. The work function of BP-ML increases by NO2 adsorption from 4.75 to 5.13 eV, while it decreases with adsorption of other NCG molecules. We have noticed that NO2 shows a considerably short recovery time of 2.21 s at T = 300 K, strongly referring to the multitime reusable nanosensor characteristic of the BP-ML surface. Additionally, the transport properties of the BP surface for the real-time sensing application are investigated by using the nonequilibrium Green’s function (NEGF) approach. The current–voltage (I–V) characteristics indicate a significant (moderate) change along the armchair (zigzag) direction when the NO2 molecule is adsorbed on the BP-ML surface. These findings suggest that BP-ML surface-based sensors are highly sensitive for the detection of NO2 molecules with short recovery time.