Augmented ammonia sensing of ion-beam modified MoSe2

Abstract

Gas sensors based on nanostructured transition metal dichalcogenides, such as MoSe2, are increasingly becoming important due to their low band gap, good electrical conductivity and selectivity. However, some of the parameters related to the gas adsorption can be tuned to enhance the overall sensing performance. The change of response sometimes remains low because of small number of active interaction sites on the surface. There are challenges related to slow response and slow recovery of the sensor. Furthermore, if the surface is hydrophilic, it can attract moisture, which may reduce interactions with the target gas and may also reduce the lifetime of the sensor. In this study we have used ion irradiation technique to overcome these challenges and exploit theoretical models to explain the physics behind enhanced sensing performance of 3D nanostructured MoSe2. A low energy (5 keV) argon ions have been used to induce structural and morphological modification of MoSe2. The irradiation leads to formation of Mo and Se vacancies, which is predicted by ion-solid interaction simulation and corroborated with various characterization techniques. The surface becomes superhydrophobic after irradiation and a significant increase of electrical conductivity takes place. We found that the ammonia sensing response increases by about 60 % due to the irradiation. There are further significant gains of response and recovery time of the sensor, post-irradiation. The response of irradiated samples shows more stability as compared to the pristine sample over a period of 180 days. First principles-based calculation points out that the charge transfer happens from surface to ammonia during the interaction and ion irradiation induced vacancies lead to better adsorption of ammonia in case of irradiated sample than that of the pristine sample.