  Combined diverse two-dimensional (2D) materials for semiconductor interfaces
are attractive for electrically controllable carrier confinement to enable
excellent electrostatic control. We investigated the transport characteristic
in heterointerface of multilayer molybdenum disulfide and hexagonal boron
nitride (MoS$_2$/h-BN) to reveal that the charge transfer switching (CTS) is
highly dependent on both the local gate constriction and bias in the channel.
Notably, the CTS is shown to be controlled at a molecular level through
electrotunable gated constriction. The resulting significant change in
conductance due to exposing 100 parts-per-billion of nitrogen dioxide gas led
to a high on/off ratio of 10 2 for completely switching off the channel thus,
acting as a molecular switch. First-principle calculations further explained
the mechanism of molecular CTS in the device. The molecular tunability of CTS
has not been previously reported in any of the van der Waals semiconductor
interfaces. Our finding opens avenues to exploit various atomically thin
heterostructures for the mesoscopic transport phenomena towards molecular
switching operation at room temperature.
