Imaging the Flow of Holes from a Collimating Contact in Graphene
Sagar Bhandari (1, 2), Mary Kreidel (1), Alexander Kelser (3),, Gil-Ho Lee (3, 4), Kenji Watanabe (5), Takashi Taniguchi (5), Philip Kim, (1, 3), Robert M Westervelt (1, 3) ((1) School of Engineering and, Applied Sciences, Harvard University, Cambridge MA, USA, (2) Department of
TL;DR
This paper uses a liquid-He cooled SPM to image hole flow in graphene, confirming collimation and trajectory bending with magnetic fields, supported by ray-tracing simulations.
Contribution
It introduces a novel method to visualize and confirm hole collimation and flow patterns in graphene using SPM imaging.
Findings
Holes exhibit a mean free path greater than device dimensions.
Patterned absorption affects hole flow at large angles.
Magnetic fields bend hole trajectories as predicted.
Abstract
A beam of holes formed in graphene by a collimating contact is imaged using a liquid-He cooled scanning probe microscope (SPM). The mean free path of holes is greater than the device dimensions. A zigzag shaped pattern on both sides of the collimating contact absorb holes that enter at large angles. The image charge beneath the SPM tip defects holes, and the pattern of flow is imaged by displaying the change in conductance between contacts on opposite sides, as the tip is raster scanned across the sample. Collimation is confirmed by bending hole trajectories away from the receiving contact with an applied magnetic field. The SPM images agree well with ray-tracing simulations.
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