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Condensed Matter - NANOSCALE IMAGING OF 2D MATERIALS UNDER GATE CONTROL AND PHOTO-EXCITATION

Seminar

Physics & Astronomy

By: Keji Lai
From: University of Texas at Austin
When: Monday, April 24, 2017
4:00 PM - 5:00 PM
Where: Brockman Hall for Physics
300
Abstract: The understanding of various types of disorders in layered transition-metal dichalcogenides, including dangling bonds at the edges, defects in the bulk, and charges in the substrate, is of fundamental importance for their applications in electronics and photonics. Because of the imperfections, electrons moving on the 2D plane experience a spatially non-uniform Coulomb environment, whose effect on the charge transport has not been microscopically probed. Using a non-invasive microwave impedance microscope with ~100nm resolution and ~1nS sensitivity, we can visualize the spatial evolution of the insulator-to-metal transition in few-layer MoS2 and MoSe2/WSe2 vertical hetero-junction field-effect transistors. Both the conductive states at sample edges and electrical inhomogeneity in the bulk are vividly seen in the microwave images. A similar conductance evolution can be observed for 2D sheets under laser illumination, showing a 100-fold increase of photoconductivity in the alloy region of the WS2/WS(1-x)Sex/WS2 multi-junction sample. The combination of novel devices and impedance microscopy paves the way to study phase transitions in complex materials.