First principles characterization of defect-free and vacancy-defected monolayer PtSe2 gas sensors

Abstract

In this paper, we investigate the gas sensing properties of pristine and vacancy-defected monolayer PtSe2 in the presence of NH3, NO2, NO, O2, and CO gas molecules. The current-voltage (I–V) characteristics as well as dielectric functions are calculated before and after gas adsorption using a non-equilibrium Green’s function (NEGF) formalism. The first-principles calculations reveal that the bandgap of PtSe2 decreases in the presence of NO, NO2, and O2 which lowers required bias voltages to drive the current, while presence of NH3 and CO gas molecules has no considerable effect on the bandgap and I–V characteristic of the sensor. Furthermore, adsorption of NO and NO2 on PtSe2 monolayer leads to the negative differential resistance in corresponding I–V characteristic. Adsorption of O2 on the sensor, especially on the pristine monolayer, increases the conductivity of sensor. From the optical properties point of view, NO2 and NO gas molecules induce new peaks at different energies in the optical absorption spectrum of the pristine and defective sensors, while O2 only modulates the absorption spectrum of the defect-free structure. At the presence of CO, the main energy peak of the spectrum shifts, whereas the presence of NH3 does not modulate the optical absorption spectrum considerably.