Charge Transfer within the F₄TCNQ‐MoS₂ van der Waals Interface: Toward Electrical Properties Tuning and Gas Sensing Application

Abstract

The development of van der Waals heterostructures in 2D materials systems has attracted considerable interests for exploring new insights of (opto‐) electrical characteristics, device physics, and novel functional applications. Utilizing organic molecular material with strong electron withdrawing ability, charge transfer van der Waals interfaces are formed between 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) and MoS2, via which the modulation of the onset voltages and optimization of subthreshold swing values in MoS2‐based field effect transistors are realized. Charge transfer process and its functionality mechanisms are further verified and investigated with first‐principles calculation, scanning Kelvin probe microscope characterization, and temperature‐dependent electrical characterization. With the charge transfer effect between reducing gas molecules and F4TCNQ, NH3 gas sensor is proposed and fabricated with the sensitivity reaching higher than 1000% at 100 ppm, much more outstanding performance than those of any reported MoS2‐based NH3 gas sensors. The F4TCNQ‐MoS2 hybrid strategy might open up a pathway for tuning and optimizing the electrical properties, in addition to novel functional units designing and fabrications in electric devices based on low‐dimensional semiconducting systems.

Optimization of Electrical Properties of MoS2 Field‐Effect Transistors by Dipole Layer Coulombic Interaction With Trap States

“…However, large negative threshold voltage ( V TH ), induced by MoS 2 intrinsic defects and interface donor states, would result in extensive power consumption and impede practical applications of MoS 2 FETs . Literatures have reported charge transfer methods via coating organic molecules on surface of MoS 2 surface and organic seimiconductor for the purpose of tuning the V TH of FET …”

“…Generally, an important factor affecting V TH is deep traps’ density, which can be modulated by two kinds of methods, such as, introducing additional deep traps and directly converting the traps from the shallow into the deep ones, of which, the later one has been realized in this work. In general, SS affected by the interface defects or other disorders between MoS 2 and gate dielectric layer .…”

MoS2 Van der Waals p–n Junctions Enabling Highly Selective Room‐Temperature NO2 Sensor

“…Heterostructures, especially p–n junctions of 2D materials, are recently attracting increasing attention for their implementation in nanodevices. [ 23–28 ] Van der Waals heterostructures formed by stacking of various 2D materials display physical properties that are between those of the two materials and display a carrier concentration gradient at their interface. Owing to the atomic thickness, the carrier concentration and energy band diagram of the heterostructure can be effectively modulated by various means, e.g., electrical, magnetic, and optical, enabling new possibilities for high‐performance gas sensors.…”

Demonstration of the key substrate-dependent charge transfer mechanisms between monolayer MoS2 and molecular dopants

“…Various methods have been proposed for tuning E F within the band gap of TMDCs, including substitution with dopant atoms 15 , stacking with other 2D materials 16 , exposure to gases [6][7][8]17 , adsorption of alkali metals 18,19 , and adsorption of organic molecules [20][21][22][23][24][25][26] . In accordance with this approach, deposition of molecular electron acceptors or donors on TMDCs has been suggested as a very effective strategy for controlling the E F position via doping, and accordingly high-performance TFTs were realized 22,24,26 . However, the extent to which the changes in electrical TFT characteristics were indeed due to electron transfer between the dopant molecules and the monolayer TMDC (ML-TMDC) was not unambiguously demonstrated, and mostly changes of photoluminescence intensity of excitons versus trions were interpreted as signature of charge transfer (CT).…”