Sensing By Surface Work Function Modulation: High Performance Gas Sensing Using Van Der Waals Stacked Bipolar Junction Transistor

We propose and demonstrate a new principle for sensing. Impact of light, radiation, charge particle and gas molecular etc. can induce the change of the surface work function of a solid. This will result in a profound effect to a device's output, such as current and voltage. Such an effect is in particular outstanding in a nanodevice using van der Waals stacked two-dimensional (2D) atomic crystals. In this paper, a study of a gas sensing device relying on such a principle is presented. Van der Waals bipolar junction transistors (V2D-BJT) based on vertically stacked MoS2/WSe2/MoS2 and WSe2/MoS2/WSe2 heterostructures are separately fabricated to detect NH3 and NO2 gas. Kelvin probe force microscope measurement shows that the work function change at the overlapped region of MoS2/WSe2/MoS2 heterostructure upon exposure to 50 ppm NH3 gas is 80 meV. In addition, the MoS2/WSe2/MoS2 V2D-BJT manifest superior sensing performances in detecting NH3, while the WSe2/MoS2/WSe2 V2D-BJT exhibited superior NO2 sensing properties in terms of high sensitivity (18), low power dissipation (12 nW), fast response (26 s) and recovery (14 s) time. We demonstrate that the NH3 and NO2 gas can be selectively detected by the V2D-BJT through changing the van der Waals heterostructure stacking sequences.