Enhanced NO<sub>2</sub> Gas Sensing in Nanocrystalline\nMoS<sub>2</sub> via Swift Heavy Ion Irradiation: An Experimental and\nDFT Study

Nanostructured\ntransition metal dichalcogenides (TMDs) like MoS<sub>2</sub> hold\npromise for gas sensing applications due to their exceptional\nproperties. However, limitations exist in maximizing sensor performance,\nsuch as limited active sites for gas interaction and sluggish response/recovery\ntimes. This study explores swift heavy ion (SHI) irradiation as a\nstrategy to address these challenges in MoS<sub>2</sub>-based NO<sub>2</sub> gas sensors. MoS<sub>2</sub> nanoflakes were fabricated and\nsubsequently irradiated with 120 MeV silver (Ag) ions to induce structural\nand morphological modifications. Characterization techniques confirmed\nthe formation of Mo and S vacancies within the MoS<sub>2</sub> lattice\ndue to irradiation. Significantly, SHI irradiation resulted in a remarkable\nenhancement of approximately 3 times improvement in sensing response\ncompared to pristine MoS<sub>2</sub> sensors. Additionally, the irradiated\nsensors exhibit substantial improvements in both response and recovery\ntimes for NO<sub>2</sub> detection. SHI irradiation resulted in the\nformation of self-affine nanostructures and increased grain fragmentation\nas fluence rises. This enhanced surface area is hypothesized to promote\ngas-sensor response. To gain deeper insights into the underlying mechanism,\nfirst-principles calculations were employed. These calculations suggest\nthat electron transfer occurs from the MoS<sub>2</sub> surface to\nthe NO<sub>2</sub> molecule during interaction. Furthermore, the irradiation-induced\nvacancies facilitate stronger NO<sub>2</sub> adsorption on the MoS<sub>2</sub> surface compared to the pristine sample. This work demonstrates\nthe effectiveness of SHI irradiation in engineering defects within\nMoS<sub>2</sub> nanoflakes, leading to significantly improved NO<sub>2</sub> gas-sensing performance. This approach offers a promising\navenue for developing next-generation TMD-based gas sensors with enhanced\nsensitivity, response times, and stability.