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# Imaging electron flow from collimating contacts in graphene

The ballistic motion of electrons in graphene encapsulated in hexagonal boron nitride (hBN) promises exciting opportunities for electron-optics devices. A narrow electron beam is desired, with both the mean free path and coherence length exceeding the device size. One can form a collimating contact... Full description

 Main Author: Bhandari, Sagar Other Authors: Lee, Gil-Ho , Watanabe, Kenji , Taniguchi, Takashi , Kim, Philip , Westervelt, Robert M Format: Electronic Article Language: Subjects: Quelle: Cornell University ID: Arxiv ID: 1710.10186 Zum Text:
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 recordid: arxiv1710.10186 title: Imaging electron flow from collimating contacts in graphene format: Article creator: Bhandari, Sagar Lee, Gil-Ho Watanabe, Kenji Taniguchi, Takashi Kim, Philip Westervelt, Robert M subjects: Condensed Matter - Mesoscale And Nanoscale Physics ispartof: description: The ballistic motion of electrons in graphene encapsulated in hexagonal boron nitride (hBN) promises exciting opportunities for electron-optics devices. A narrow electron beam is desired, with both the mean free path and coherence length exceeding the device size. One can form a collimating contact in graphene by adding zigzag contacts on either side of the electron emitter that absorb stray electrons to form a collimated electron beam [23]. Here we provide images of electron flow from a collimating contact that directly show the width and shape of the electron beam, obtained using a Scanning Gate Microscope (SGM) cooled to 4.2 K. The device is a hBN-encapsulated graphene hall bar with narrow side contacts on either side of the channel that have an electron emitter at the end and absorbing zig-zag contacts at both side. To form an image of electron flow, the SGM tip is raster scanned at a constant height above the sample surface while the transmission to a receiving contact on opposite sides of the channel is measured. By displaying the change {\Delta}T vs. tip position, an image of ballistic flow is obtained. The angular width of the electron beam leaving the collimating contact is found by applying a perpendicular magnetic field B that bends electron paths into cyclotron orbits. SGM images reveal that electron flow from a collimating contact disappears quickly at B = 0.05T while the flow from a non-collimating contact persists up to B = 0.19 T. Ray tracing simulations agree well with the experimental images over a range of B and electron density n. By fitting the half-width at half-max (HWHM) of the magnitude of electron flow in the experimental SGM images, we find a narrow half angular width {\Delta}{\theta} = 9.2{\deg} for the electron flow from the collimating contact, compared with a wide flow {\Delta}{\theta} = 54{\deg} from the non-collimating contact. Comment: 9 pages, 6 figures language: source: Cornell University identifier: Arxiv ID: 1710.10186 fulltext: fulltext_linktorsrc url: Link

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 type article title Imaging electron flow from collimating contacts in graphene creator Bhandari, Sagar ; Lee, Gil-Ho ; Watanabe, Kenji ; Taniguchi, Takashi ; Kim, Philip ; Westervelt, Robert M identifier Arxiv ID: 1710.10186 subject Condensed Matter - Mesoscale And Nanoscale Physics description The ballistic motion of electrons in graphene encapsulated in hexagonal boron nitride (hBN) promises exciting opportunities for electron-optics devices. A narrow electron beam is desired, with both the mean free path and coherence length exceeding the device size. One can form a collimating contact in graphene by adding zigzag contacts on either side of the electron emitter that absorb stray electrons to form a collimated electron beam [23]. Here we provide images of electron flow from a collimating contact that directly show the width and shape of the electron beam, obtained using a Scanning Gate Microscope (SGM) cooled to 4.2 K. The device is a hBN-encapsulated graphene hall bar with narrow side contacts on either side of the channel that have an electron emitter at the end and absorbing zig-zag contacts at both side. To form an image of electron flow, the SGM tip is raster scanned at a constant height above the sample surface while the transmission to a receiving contact on opposite sides of the channel is measured. By displaying the change {\Delta}T vs. tip position, an image of ballistic flow is obtained. The angular width of the electron beam leaving the collimating contact is found by applying a perpendicular magnetic field B that bends electron paths into cyclotron orbits. SGM images reveal that electron flow from a collimating contact disappears quickly at B = 0.05T while the flow from a non-collimating contact persists up to B = 0.19 T. Ray tracing simulations agree well with the experimental images over a range of B and electron density n. By fitting the half-width at half-max (HWHM) of the magnitude of electron flow in the experimental SGM images, we find a narrow half angular width {\Delta}{\theta} = 9.2{\deg} for the electron flow from the collimating contact, compared with a wide flow {\Delta}{\theta} = 54{\deg} from the non-collimating contact. Comment: 9 pages, 6 figures source Cornell University oa free_for_read
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 0 Bhandari, Sagar 1 Lee, Gil-Ho 2 Watanabe, Kenji 3 Taniguchi, Takashi 4 Kim, Philip 5 Westervelt, Robert M
titleImaging electron flow from collimating contacts in graphene
description
 0 The ballistic motion of electrons in graphene encapsulated in hexagonal boron nitride (hBN) promises exciting opportunities for electron-optics devices. A narrow electron beam is desired, with both the mean free path and coherence length exceeding the device size. One can form a collimating contact in graphene by adding zigzag contacts on either side of the electron emitter that absorb stray electrons to form a collimated electron beam [23]. Here we provide images of electron flow from a collimating contact that directly show the width and shape of the electron beam, obtained using a Scanning Gate Microscope (SGM) cooled to 4.2 K. The device is a hBN-encapsulated graphene hall bar with narrow side contacts on either side of the channel that have an electron emitter at the end and absorbing zig-zag contacts at both side. To form an image of electron flow, the SGM tip is raster scanned at a constant height above the sample surface while the transmission to a receiving contact on opposite sides of the channel is measured. By displaying the change {\Delta}T vs. tip position, an image of ballistic flow is obtained. The angular width of the electron beam leaving the collimating contact is found by applying a perpendicular magnetic field B that bends electron paths into cyclotron orbits. SGM images reveal that electron flow from a collimating contact disappears quickly at B = 0.05T while the flow from a non-collimating contact persists up to B = 0.19 T. Ray tracing simulations agree well with the experimental images over a range of B and electron density n. By fitting the half-width at half-max (HWHM) of the magnitude of electron flow in the experimental SGM images, we find a narrow half angular width {\Delta}{\theta} = 9.2{\deg} for the electron flow from the collimating contact, compared with a wide flow {\Delta}{\theta} = 54{\deg} from the non-collimating contact. 1 Comment: 9 pages, 6 figures
subjectCondensed Matter - Mesoscale and Nanoscale Physics
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abstractThe ballistic motion of electrons in graphene encapsulated in hexagonal boron nitride (hBN) promises exciting opportunities for electron-optics devices. A narrow electron beam is desired, with both the mean free path and coherence length exceeding the device size. One can form a collimating contact in graphene by adding zigzag contacts on either side of the electron emitter that absorb stray electrons to form a collimated electron beam [23]. Here we provide images of electron flow from a collimating contact that directly show the width and shape of the electron beam, obtained using a Scanning Gate Microscope (SGM) cooled to 4.2 K. The device is a hBN-encapsulated graphene hall bar with narrow side contacts on either side of the channel that have an electron emitter at the end and absorbing zig-zag contacts at both side. To form an image of electron flow, the SGM tip is raster scanned at a constant height above the sample surface while the transmission to a receiving contact on opposite sides of the channel is measured. By displaying the change {\Delta}T vs. tip position, an image of ballistic flow is obtained. The angular width of the electron beam leaving the collimating contact is found by applying a perpendicular magnetic field B that bends electron paths into cyclotron orbits. SGM images reveal that electron flow from a collimating contact disappears quickly at B = 0.05T while the flow from a non-collimating contact persists up to B = 0.19 T. Ray tracing simulations agree well with the experimental images over a range of B and electron density n. By fitting the half-width at half-max (HWHM) of the magnitude of electron flow in the experimental SGM images, we find a narrow half angular width {\Delta}{\theta} = 9.2{\deg} for the electron flow from the collimating contact, compared with a wide flow {\Delta}{\theta} = 54{\deg} from the non-collimating contact.