Enhanced NO₂ Gas Sensing in Nanocrystalline MoS₂ via Swift Heavy Ion Irradiation: An Experimental and DFT Study

Nanostructured transition metal dichalcogenides (TMDs) like MoS₂ hold promise for gas sensing applications due to their exceptional properties. However, limitations exist in maximizing sensor performance, such as limited active sites for gas interaction and sluggish response/recovery times. This study explores swift heavy ion (SHI) irradiation as a strategy to address these challenges in MoS₂-based NO₂ gas sensors. MoS₂ nanoflakes were fabricated and subsequently irradiated with 120 MeV silver (Ag) ions to induce structural and morphological modifications. Characterization techniques confirmed the formation of Mo and S vacancies within the MoS₂ lattice due to irradiation. Significantly, SHI irradiation resulted in a remarkable enhancement of approximately 3 times improvement in sensing response compared to pristine MoS₂ sensors. Additionally, the irradiated sensors exhibit substantial improvements in both response and recovery times for NO₂ detection. SHI irradiation resulted in the formation of self-affine nanostructures and increased grain fragmentation as fluence rises. This enhanced surface area is hypothesized to promote gas-sensor response. To gain deeper insights into the underlying mechanism, first-principles calculations were employed. These calculations suggest that electron transfer occurs from the MoS₂ surface to the NO₂ molecule during interaction. Furthermore, the irradiation-induced vacancies facilitate stronger NO₂ adsorption on the MoS₂ surface compared to the pristine sample. This work demonstrates the effectiveness of SHI irradiation in engineering defects within MoS₂ nanoflakes, leading to significantly improved NO₂ gas-sensing performance. This approach offers a promising avenue for developing next-generation TMD-based gas sensors with enhanced sensitivity, response times, and stability.