Selective Gas Sensing With $h$ -BN Capped MoS 2 Heterostructure Thin-Film Transistors

Owing to their ultimate surface-to-volume ratio two-dimensional (2D) van der Waals materials are candidates for flexible gas sensor applications. However, all demonstrated devices had relied on direct exposure of the active 2D channel to gases, which presents problems for their reliability and stability. We demonstrated, for the first time, selective gas sensing with molybdenum disulfide (MoS 2 ) thin films transistors capped with a thin layer of hexagonal boron nitride ( $h$ -BN). The resistance change, $\Delta R/R$ , was used as a sensing parameter to detect chemical vapors. It was found that $h$ -BN dielectric passivation layer does not prevent gas detection via changes in the current in the MoS 2 channel. The detection without direct contacting the channel with analyte molecules was achieved with $\Delta R/R$ ratio as high as $10^{\mathrm { {3}}}$ . In addition, we show that the use of $h$ -BN cap layers (thickness $H \sim 10$ nm) improves sensor stability and prevents degradation due to environmental and chemical exposure.