Synergetic effect of electrostatic gating and interfacial states in molecular switching operation in molybdenum disulfide based thin hetero-interfaces

Abstract

Nowadays, two-dimensional (2D) materials have stimulated intensive research due to their intriguing physical properties and excellent electronic application. van der Waals (vdW) semiconductors are attractive for electrically controllable carrier confinement, combined with the diverse nature of 2D materials that enable superior electrostatic control. Molecular interaction in two-dimensional van der Waals interfaces has drawn tremendous attention for extraordinary materials characteristics. This work encompasses molecular responses study of various atomically thin heterostructures made of molybdenum disulfide (MoS2), graphene, and hexagonal boron nitride (h-BN). The defect induced interfacial states are created in an atomically thin two-dimensional MoS2 channel by underlying a narrow pattern of a graphene layer in a field-effect transistor. The presence of interfacial states in the channel leads to a conductance fluctuation. Its magnitude is modulated nearly three-order of magnitude at room temperature using the nitrogen dioxide gas molecules in the subthreshold region. The study provides a systematic approach to establishing a correlation between modulated conductance fluctuation and the molecular concentration up to parts-per-billion. First-principles density functional theory further explains the role of unique interfacial configuration on conductance fluctuation. Therefore, our study demonstrates an experimental approach to induce charge-state for the modulation of carrier concentration and exploits the role of defect induced interfacial states in atomically thin interfaces for the molecular interaction. So far, sensing molecular interaction characteristics have been exploited extensively to reach detection limit to a few parts-per-billion (ppb) of molecules. Far less attention is given to the evolution of persistent current state due to molecular exposure. Our study focuses on the molecular memory operation of MoS2-graphene heterostructure based field-effect transistor. The metastable resistance state of the device due to external perturbation of molecules is tuned to get a near relaxation free current state at a much lower molecular concentration of 10 ppb to facilitate non-volatile memory features for molecular memory operation. An ultrafast switching operation in milli-second order was achieved at room temperature for the fastest recovery obtained so far in any molecular sensor. The process is co-controlled both by molecular as well as external charge density. Along with the interface property, the proper stacking of the vdW materials can be adapted for real-time room temperature applications. Here, we investigate transport properties of a multilayer MoS2/h-BN heterojunction via a tunable electrostatic barrier using artificially designed different local gates width. A systematic transport characteristic revealed that the charge transfer switching (CTS) is a bias dependent conductance phenomenon with highly depends on local gate width and bias in the channel due to the gating constriction with an ON-OFF ratio of ~103. Furthermore, the CTS can be precisely controlled upon molecular interaction through electrotuneable gated constriction. Interestingly, the large-conductance change (102) due to the 100 ppb level of gas concentration leads to a complete switching off the channel can act as a molecular switch. Further, the mechanism of molecular CTS in the device was explained by the Fermi level shift using the first-principle calculations with nitrogen dioxide molecules adsorbed in MoS2. This precise tunability of CTS has not been previously reported in any atomically thin 2D materials. Results of molecular interaction study in van der Waals materials contribute to the research of various other types of heterostructures and can be further applied for mesoscopic transport phenomena for molecular memory, switching operation at room temperature.