期刊
NANO LETTERS
卷 18, 期 11, 页码 7200-7206出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.8b03318
关键词
van der Waals materials; monolayer-bilayer interface; edge states; microwave impedance microscopy; photoconductivity imaging
类别
资金
- National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC [DMR-1720595]
- NSF [EFMA-1542747]
- U.S. Army Research Laboratory
- U.S. Army Research Office [W911NF-16-1-0276, W911NF-17-1-0190]
- Welch Foundation [F-1662, F-1814, TBF1473]
- King Abdullah University of Science and Technology
Vertical and lateral heterostructures of van der Waals materials provide tremendous flexibility for band-structureengineering. Because electronic bands are sensitively affected by defects, strain, and interlayer coupling, the edge and heterojunction of these two-dimensional (2D) systems may exhibit novel physical properties, which can be fully revealed only by spatially resolved probes. Here, we report the spatial mapping of photoconductivity in a monolayer-bilayer WSe2 lateral heterostructure under multiple excitation lasers. As the photon energy increases, the light-induced conductivity detected by microwave impedance microscopy first appears along the heterointerface and bilayer edge, then along the monolayer edge, inside the bilayer area, and finally in the interior of the monolayer region. The sequential emergence of mobile carriers in different sections of the sample is consistent with the theoretical calculation of local energy gaps. Quantitative analysis of the microscopy and transport data also reveals the linear dependence of photoconductivity on the laser intensity and the influence of interlayer coupling on carrier recombination. Combining theoretical modeling, atomic-scale imaging, mesoscale impedance microscopy, and device-level characterization, our work suggests an exciting perspective for controlling the intrinsic band gap variation in 2D heterostructures down to a regime of a few nanometers.
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