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Title: Imaging electron flow from collimating contacts in graphene

Abstract

The ballistic motion of electrons in graphene opens exciting opportunities for electron-optic devices based on collimated electron beams. We form a collimating contact in a hBN-encapsulated graphene hall bar by adding zigzag contacts on either side of an electron emitter that absorb stray electrons; collimation can be turned off by floating the zig-zag contacts. The electron beam is imaged using a liquid-He cooled scanning gate microscope (SGM). The tip deflects electrons as they pass from the collimating contact to a receiving contact on the opposite side of the channel, and an image of electron flow can be made by displaying the change in transmission as the tip is raster scanned across the sample. The angular half width Δθ of the electron beam is found by applying a perpendicular magnetic field B that bends electron paths into cyclotron orbits. The images reveal that the electron flow from the collimating contact drops quickly at B = 0.05 T when the electron orbits miss the receiving contact. The flow for the non-collimating case persists longer, up to B = 0.19 T, due to the broader range of entry angles. Ray-tracing simulations agree well with the experimental images. By fitting the fields B atmore » which the magnitude of electron flow drops in the experimental SGM images, we find Δθ = 9° for electron flow from the collimating contact, compared with Δθ = 54° for the non-collimating case.« less

Authors:
ORCiD logo; ORCiD logo; ; ; ; ORCiD logo
Publication Date:
Research Org.:
Harvard Univ., Cambridge, MA (United States); Pohang Univ. of Science and Technology (POSTECH) (Korea, Republic of); National Institute for Materials Science (NIMS), Tsukuba (Japan)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); National Research Foundation of Korea (NRF); Japan Society for the Promotion of Science (JSPS)
OSTI Identifier:
1437836
Alternate Identifier(s):
OSTI ID: 1498664
Grant/Contract Number:  
FG02-07ER46422; ECCS-1541959; 2015K1A1A2033332
Resource Type:
Published Article
Journal Name:
2D Materials
Additional Journal Information:
Journal Name: 2D Materials Journal Volume: 5 Journal Issue: 2; Journal ID: ISSN 2053-1583
Publisher:
IOP Publishing
Country of Publication:
United Kingdom
Language:
English
Subject:
36 MATERIALS SCIENCE; graphene; cooled scanning probe microscope; collimation; ballistic electrons; imaging electrons

Citation Formats

Bhandari, S., Lee, G. H., Watanabe, K., Taniguchi, T., Kim, P., and Westervelt, R. M. Imaging electron flow from collimating contacts in graphene. United Kingdom: N. p., 2018. Web. doi:10.1088/2053-1583/aab38a.
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Bhandari, S., Lee, G. H., Watanabe, K., Taniguchi, T., Kim, P., & Westervelt, R. M. Imaging electron flow from collimating contacts in graphene. United Kingdom. https://doi.org/10.1088/2053-1583/aab38a
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Bhandari, S., Lee, G. H., Watanabe, K., Taniguchi, T., Kim, P., and Westervelt, R. M. Thu . "Imaging electron flow from collimating contacts in graphene". United Kingdom. https://doi.org/10.1088/2053-1583/aab38a.
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@article{osti_1437836,
title = {Imaging electron flow from collimating contacts in graphene},
author = {Bhandari, S. and Lee, G. H. and Watanabe, K. and Taniguchi, T. and Kim, P. and Westervelt, R. M.},
abstractNote = {The ballistic motion of electrons in graphene opens exciting opportunities for electron-optic devices based on collimated electron beams. We form a collimating contact in a hBN-encapsulated graphene hall bar by adding zigzag contacts on either side of an electron emitter that absorb stray electrons; collimation can be turned off by floating the zig-zag contacts. The electron beam is imaged using a liquid-He cooled scanning gate microscope (SGM). The tip deflects electrons as they pass from the collimating contact to a receiving contact on the opposite side of the channel, and an image of electron flow can be made by displaying the change in transmission as the tip is raster scanned across the sample. The angular half width Δθ of the electron beam is found by applying a perpendicular magnetic field B that bends electron paths into cyclotron orbits. The images reveal that the electron flow from the collimating contact drops quickly at B = 0.05 T when the electron orbits miss the receiving contact. The flow for the non-collimating case persists longer, up to B = 0.19 T, due to the broader range of entry angles. Ray-tracing simulations agree well with the experimental images. By fitting the fields B at which the magnitude of electron flow drops in the experimental SGM images, we find Δθ = 9° for electron flow from the collimating contact, compared with Δθ = 54° for the non-collimating case.},
doi = {10.1088/2053-1583/aab38a},
journal = {2D Materials},
number = 2,
volume = 5,
place = {United Kingdom},
year = {Thu Mar 22 00:00:00 EDT 2018},
month = {Thu Mar 22 00:00:00 EDT 2018}
}
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Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1088/2053-1583/aab38a
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Citation Metrics:
Cited by: 12 works
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Figures / Tables:

Figure 1 Figure 1: (a) Scanning electron micrograph of hBN-graphene-hBN device in a hall bar geometry with four collimating contacts with absorptive zig-zag sections that form a narrow electron beam. The white square shows the area imaged by the cooled SGM. The blue region indicates graphene and yellow indicates metal contacts. (b)more » Ray-tracing simulations of electrons passing through the collimating contact (yellow) through absorptive zig-zag side contacts (yellow) the half angle of exiting rays in the schematic diagram is Δθ = 7.5°. (c) Simulated image charge created by the charged tip which creates a local dip in electron density.« less
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    Works referencing / citing this record:

    Bridging scales in multiphysics VCSEL modeling
    journal, June 2019

    • Tibaldi, Alberto; González Montoya, Jesus Alberto; Bertazzi, Francesco
    • Optical and Quantum Electronics, Vol. 51, Issue 7
    • DOI: 10.1007/s11082-019-1931-8

    Super-geometric electron focusing on the hexagonal Fermi surface of PdCoO2
    journal, November 2019

    Simultaneous voltage and current density imaging of flowing electrons in two dimensions
    journal, March 2019

    Electron collimation at van der Waals domain walls in bilayer graphene
    journal, July 2019

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