Defect-Induced\nSensitivity Improvement in HfNBr Monolayers\nfor Ammonia Detection

Two-dimensional materials, owing\nto their unique physical\nproperties\nand high surface area, play a crucial role in intelligent sensing,\nparticularly in the domain of atmospheric pollutant monitoring. In\nthis work, we have extensively investigated the gas-sensing capabilities\nof the HfNBr monolayer for ammonia detection by introducing point\ndefects, utilizing density functional theory and nonequilibrium Green’s\nfunction calculations. Upon the introduction of point defects, the\nadsorption energy of HfNBr monolayers for ammonia significantly increased\n(from −0.162 to −1.257 eV), indicating a markedly strengthened\naffinity. To further elucidate the sensing mechanism, we conducted\nan in-depth investigation into the charge transfer dynamics, the density\nof states, and the charge density difference between the adsorbent\nand the adsorbate. Besides, we employed the NEGF method to evaluate\nthe changes in the current–voltage characteristics of the HfNBr\nmonolayer before and after adsorption, which revealed a remarkable\nchange in the apparent resistance, thereby demonstrating excellent\nsensitivity. The exceptional performance of the HfNBr monolayer toward\nNH<sub>3</sub> demonstrates its significant value in practical applications\nfor ammonia detection.