Designing and optimizing β1-borophene organic gas sensor: A theoretical study

Borophene, a two-dimensional (2D) boron sheet, has received widespread attention recently. β1-borophene is one of the allotropes and has the representative structure. Using density functional theory and non-equilibrium Green's function method, here we investigated the adsorption behaviors of small organic molecules CH4, CH3OH, C6H6, C2H2, C2H4, HCHO and HCOOH on β1-borophene, and the corresponding sensing applications. We found that CH4, CH3OH and C6H6 are physically adsorbed on β1-borophene while C2H2, C2H4, HCHO and HCOOH are chemically adsorbed on β1-borophene. For the cases of chemisorption, the chemical bonds of the C atoms in the four organic molecules all change to sp3 hybridization, owing to the strong interactions with β1-borophene. The transport properties of β1-borophene are sensitive to the adsorption of C2H2, C2H4, HCHO and HCOOH, thus β1-borophene can be used to construct gas sensors for the organic molecules. Especially, β1-borophene is very sensitive to C2H4 and the sensing performance can be improved by applying proper in-plane strain. In addition, the influence of the substrates has also been considered. We found that β1-borophene can form van der Waals heterostructures with 2D semiconductors MoS2, MoSe2, WS2 or WSe2, and WS2 can be chosen as the substrate since it enhances the thermal stability of β1-borophene and significantly improves the sensing performance. This suggests a possible way to design borophene-based organic gas sensors.