Drastic Improvement in Gas-Sensing Characteristics of Phosphorene Nanosheets under Vacancy Defects and Elemental Functionalization

Efficient chemical gas detection is of great importance for various functionalities (such as leakage detection of hazardous and explosive gases in industrial safety systems). The recent discovery of 2D black phosphorene (BlackP) has created intensive interests toward nanosensors because of its maximized surface-to-volume ratio and exceptional carrier mobility that potentially deliver the superior performance than the conventional transition-metal oxides sensors. In this work, we have performed first-principles DFT calculations coupled with the statistical analysis to unravel the structural, electronic, and gas-sensing characteristics of pristine, defected, and metal-substituted BlackP toward toxic H2S and SO2 gas molecules. Our findings have revealed that pristine BlackP weakly interacts with both H2S and SO2 by van der Waals (vdW) forces characterized by the small binding energies. The analysis of electronic properties via the density of states (DOS) indicates that there is a negligible change in DOS after gas exposure, which confirms insensitive sensing. To intensify the binding energies, we have considered defects (mono-, di-, tri-, and quad-vacancy) and substitutional impurities (Ti, Si, Mn, and Fe) as the incentives. The presence of mono- and divacancies remains less energetically sensitive to both gas species because of the low adsorption energies. Meanwhile, tri- and quad-vacancies induce the dissociative adsorption, not suitable for the reversible adsorption–desorption cycles. Substitutional doping by Fe atoms is found to be a feasible approach to enhance the sensing resolution of SO2 detection because of the remarkable adsorption energy incorporated with the substantial variation in DOS after gas exposure. This modification in electronic properties is facilitated by the charge transfer mechanism from Fe 3d to P 3p which can generate the measurable electrical signal detected by the external circuit of the sensor.