Pressure-induced heavy doping in the graphene/MoS2 heterostructure – Dr. Jungfu Lin
Shanghai, June 21, 2016 — New work coauthored by HPSTAR scientist, Jungfu "Afu" Lin, found a unique way- hydrostatic pressure for achieving controllable charge transfer doping in the graphene/MoS2 heterostructure. This research sheds light on how modification of interactions in a heterostructure under pressure can lead to many fold enhancements in carrier concentration of graphene. The story is published in Small.
Graphene is the world’s thinnest, strongest and most conductive material, and has the potential to revolutionize a huge number of diverse applications. With no natural energy band-gap, however, graphene's superfast conductance can't be switched off, a serious drawback for transistors and other electronic devices. Various techniques have been deployed to overcome this problem with one of the most promising being the integration of ultrathin layers of graphene and other 2D materials into two-dimensional Van der Waals heterostructures.
Van der Waals heterostructures open a new sub-area in the research on 2D materials and pave the way for novel electronics following the discovery of grapheme and other 2D materials. The combinations of 2D crystals allow researchers to achieve functionality not available from any of the individual materials.
Among these 2D materials, MoS2, a well-studied 2D semiconductor, can form a transistor that can be switched fully ‘off’. “This character is well suited to serve as the channel material in field-effect transistor applications, exhibiting high mobility, almost ideal switching characteristics, and low standby power dissipation,” said Lin, a staff scientist of HPSTAR and a co-author of the work.
Their previous high-pressure studies on transition metal dichalcogenides has proved that the electronic structure of these materials are very sensitive to external stress (WS2, Nayak et al., ACS Nano, 2015) and MoS2 Nano Letters, 2014).
In the present study, the researchers also expected to tune the carrier mobility and conductivity of heterostructured monolayer grapheme and 2H-MoS2 using the same technique-diamond anvil cell, realizing high pressure.
The two typical Raman bands of graphene in graphene/MoS2 heterostructure deviates significantly from the freestanding graphene and exhibit a strong pressure dependence. The pressure-dependent intensity variations for the two bands are consistent with hole/p-tybe doping. Moreover, the doping level exponentially increases with pressure to the heaviest doping concentration so far in the grapheme/MoS2 heterstructure.
Caption: Electronic charge transfer at the monolayer graphene/MoS2 interface at high pressure, courtesy of Tribhuwan Pandey.
“Hydrostatic pressure points out a clear approach to realize the p-type doping in graphene in the graphene/MoS2 heterostructure”, said Afu Lin. “It could be applied to tune the electronic structures of other van der Waals heterostructures at extreme environments.