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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

 Journal Title: arXiv.org Oct 27, 2017 Main Author: Bhandari, Sagar Other Authors: Gil-Ho, Lee , Watanabe, Kenji , Taniguchi, Takashi , Kim, Philip , Westervelt, Robert Format: Electronic Article Language: English Subjects: Quelle: © ProQuest LLC All rights reserved Zum Text:
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 recordid: proquest2076856134 title: Imaging electron flow from collimating contacts in graphene format: Article creator: Bhandari, Sagar Gil-Ho, Lee Watanabe, Kenji Taniguchi, Takashi Kim, Philip Westervelt, Robert subjects: Electrons Position Measurement Ray Tracing Electron Beams Collimation Encapsulation Graphene Cyclotrons Angular Position Raster Scanning Bends Electron Density Emitters (Electron) Electron Trajectories Images Coherence Length Boron Nitride Contact Angle ispartof: arXiv.org, Oct 27, 2017 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. language: eng source: © ProQuest LLC All rights reserved identifier: fulltext: fulltext_linktorsrc url: Link

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titleImaging electron flow from collimating contacts in graphene
creatorBhandari, Sagar ; Gil-Ho, Lee ; Watanabe, Kenji ; Taniguchi, Takashi ; Kim, Philip ; Westervelt, Robert
contributorWestervelt, Robert (pacrepositoryorg)
ispartofarXiv.org, Oct 27, 2017
subjectElectrons ; Position Measurement ; Ray Tracing ; Electron Beams ; Collimation ; Encapsulation ; Graphene ; Cyclotrons ; Angular Position ; Raster Scanning ; Bends ; Electron Density ; Emitters (Electron) ; Electron Trajectories ; Images ; Coherence Length ; Boron Nitride ; Contact Angle
descriptionThe 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.
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 0 Bhandari, Sagar 1 Gil-Ho, Lee 2 Watanabe, Kenji 3 Taniguchi, Takashi 4 Kim, Philip 5 Westervelt, Robert
titleImaging electron flow from collimating contacts in graphene
descriptionThe 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.
subject
 0 Electrons 1 Position Measurement 2 Ray Tracing 3 Electron Beams 4 Collimation 5 Encapsulation 6 Graphene 7 Cyclotrons 8 Angular Position 9 Raster Scanning 10 Bends 11 Electron Density 12 Emitters (Electron) 13 Electron Trajectories 14 Images 15 Coherence Length 16 Boron Nitride 17 Contact Angle
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startdate20171027
enddate20171027
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 title Imaging electron flow from collimating contacts in graphene author Bhandari, Sagar ; Gil-Ho, Lee ; Watanabe, Kenji ; Taniguchi, Takashi ; Kim, Philip ; Westervelt, Robert creationdate 20171027 lso01 20171027
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 0 Electrons 1 Position Measurement 2 Ray Tracing 3 Electron Beams 4 Collimation 5 Encapsulation 6 Graphene 7 Cyclotrons 8 Angular Position 9 Raster Scanning 10 Bends 11 Electron Density 12 Emitters (Electron) 13 Electron Trajectories 14 Images 15 Coherence Length 16 Boron Nitride 17 Contact Angle
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atitleImaging electron flow from collimating contacts in graphene
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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.
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pubCornell University Library, arXiv.org
urlhttp://search.proquest.com/docview/2076856134/