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Title: Analysis of Scanned Probe Images for Magnetic Focusing in Graphene

Abstract

We have used cooled scanning probe microscopy (SPM) to study electron motion in nanoscale devices. The charged tip of the microscope was raster-scanned at constant height above the surface as the conductance of the device was measured. The image charge scatters electrons away, changing the path of electrons through the sample. Using this technique, we imaged cyclotron orbits that flow between two narrow contacts in the magnetic focusing regime for ballistic hBN–graphene–hBN devices. We present herein an analysis of our magnetic focusing imaging results based on the effects of the tip-created charge density dip on the motion of ballistic electrons. The density dip locally reduces the Fermi energy, creating a force that pushes electrons away from the tip. When the tip is above the cyclotron orbit, electrons are deflected away from the receiving contact, creating an image by reducing the transmission between contacts. The data and our analysis suggest that the graphene edge is rather rough, and electrons scattering off the edge bounce in random directions. However, when the tip is close to the edge, it can enhance transmission by bouncing electrons away from the edge, toward the receiving contact. Our results demonstrate that cooled SPM is a promising toolmore » to investigate the motion of electrons in ballistic graphene devices.« less

Authors:
 [1];  [2];  [3];  [3]
  1. Harvard Univ., Cambridge, MA (United States). School of Engineering and Applied Sciences
  2. Harvard Univ., Cambridge, MA (United States). Dept. of Physics
  3. Harvard Univ., Cambridge, MA (United States). School of Engineering and Applied Sciences. Dept. of Physics
Publication Date:
Research Org.:
Harvard Univ., Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); US Air Force Office of Scientific Research (AFOSR); National Science Foundation (NSF)
OSTI Identifier:
1344318
Alternate Identifier(s):
OSTI ID: 1423801
Grant/Contract Number:
FG02-07ER46422; FA9550-13-1-0211
Resource Type:
Journal Article: Published Article
Journal Name:
Journal of Electronic Materials
Additional Journal Information:
Journal Volume: 46; Journal Issue: 7; Journal ID: ISSN 0361-5235
Publisher:
Springer
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 47 OTHER INSTRUMENTATION; scanning probe microscopy theory; ballistic transport; graphene; simulation; magnetic focusing; electron trajectories

Citation Formats

Bhandari, Sagar, Lee, Gil-Ho, Kim, Philip, and Westervelt, Robert M. Analysis of Scanned Probe Images for Magnetic Focusing in Graphene. United States: N. p., 2017. Web. doi:10.1007/s11664-017-5350-y.
Bhandari, Sagar, Lee, Gil-Ho, Kim, Philip, & Westervelt, Robert M. Analysis of Scanned Probe Images for Magnetic Focusing in Graphene. United States. doi:10.1007/s11664-017-5350-y.
Bhandari, Sagar, Lee, Gil-Ho, Kim, Philip, and Westervelt, Robert M. Tue . "Analysis of Scanned Probe Images for Magnetic Focusing in Graphene". United States. doi:10.1007/s11664-017-5350-y.
@article{osti_1344318,
title = {Analysis of Scanned Probe Images for Magnetic Focusing in Graphene},
author = {Bhandari, Sagar and Lee, Gil-Ho and Kim, Philip and Westervelt, Robert M.},
abstractNote = {We have used cooled scanning probe microscopy (SPM) to study electron motion in nanoscale devices. The charged tip of the microscope was raster-scanned at constant height above the surface as the conductance of the device was measured. The image charge scatters electrons away, changing the path of electrons through the sample. Using this technique, we imaged cyclotron orbits that flow between two narrow contacts in the magnetic focusing regime for ballistic hBN–graphene–hBN devices. We present herein an analysis of our magnetic focusing imaging results based on the effects of the tip-created charge density dip on the motion of ballistic electrons. The density dip locally reduces the Fermi energy, creating a force that pushes electrons away from the tip. When the tip is above the cyclotron orbit, electrons are deflected away from the receiving contact, creating an image by reducing the transmission between contacts. The data and our analysis suggest that the graphene edge is rather rough, and electrons scattering off the edge bounce in random directions. However, when the tip is close to the edge, it can enhance transmission by bouncing electrons away from the edge, toward the receiving contact. Our results demonstrate that cooled SPM is a promising tool to investigate the motion of electrons in ballistic graphene devices.},
doi = {10.1007/s11664-017-5350-y},
journal = {Journal of Electronic Materials},
number = 7,
volume = 46,
place = {United States},
year = {Tue Feb 21 00:00:00 EST 2017},
month = {Tue Feb 21 00:00:00 EST 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1007/s11664-017-5350-y

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  • We have used cooled scanning probe microscopy (SPM) to study electron motion in nanoscale devices. The charged tip of the microscope was raster-scanned at constant height above the surface as the conductance of the device was measured. The image charge scatters electrons away, changing the path of electrons through the sample. Using this technique, we imaged cyclotron orbits that flow between two narrow contacts in the magnetic focusing regime for ballistic hBN–graphene–hBN devices. We present herein an analysis of our magnetic focusing imaging results based on the effects of the tip-created charge density dip on the motion of ballistic electrons.more » The density dip locally reduces the Fermi energy, creating a force that pushes electrons away from the tip. When the tip is above the cyclotron orbit, electrons are deflected away from the receiving contact, creating an image by reducing the transmission between contacts. The data and our analysis suggest that the graphene edge is rather rough, and electrons scattering off the edge bounce in random directions. However, when the tip is close to the edge, it can enhance transmission by bouncing electrons away from the edge, toward the receiving contact. Our results demonstrate that cooled SPM is a promising tool to investigate the motion of electrons in ballistic graphene devices.« less
  • A technique for the analysis of photoelectrically scanned double star images is described. The method consists of comparimg the Fourier transform of the double star profile with that of a single star profile imaged through the same telescope. If the measured profile of the double star iinage can be considered to be a linear superposition of two profiles, each identical in shape to the measured profile of a mearby single star, a comparison of the Fourier transforms of these profiles enables the parameters of the double star system to be determimed. Certain features of the ratio of the moduli ofmore » the transforms yield both the separation and the magnitude difference betweem the compoments. A comparison of the phases of the transforms enables one to establish which of the two components is the brighter. (auth)« less
  • Purpose: To estimate attenuation using cross sectional CT images and scanned projection radiograph (SPR) images in a series of thorax and abdomen phantoms. Methods: Attenuation was quantified in terms of a water cylinder with cross sectional area of A{sub w} from both the CT and SPR images of abdomen and thorax phantoms, where A{sub w} is the area of a water cylinder that would absorb the same dose as the specified phantom. SPR and axial CT images were acquired using a dual-source CT scanner operated at 120 kV in single-source mode. To use the SPR image for estimating A{sub w},more » the pixel values of a SPR image were calibrated to physical water attenuation using a series of water phantoms. A{sub w} and the corresponding diameter D{sub w} were calculated using the derived attenuation-based methods (from either CT or SPR image). A{sub w} was also calculated using only geometrical dimensions of the phantoms (anterior-posterior and lateral dimensions or cross sectional area). Results: For abdomen phantoms, the geometry-based and attenuation-based methods gave similar results for D{sub w}. Using only geometric parameters, an overestimation of D{sub w} ranging from 4.3% to 21.5% was found for thorax phantoms. Results for D{sub w} using the CT image and SPR based methods agreed with each other within 4% on average in both thorax and abdomen phantoms. Conclusions: Either the cross sectional CT or SPR images can be used to estimate patient attenuation in CT. Both are more accurate than use of only geometrical information for the task of quantifying patient attenuation. The SPR based method requires calibration of SPR pixel values to physical water attenuation and this calibration would be best performed by the scanner manufacturer.« less
  • Descriptions are given of an instrument for measuring and stabilizing a magnetic field. The region of measurement and stabilization of the field is from 5 to 200 gauss. Relative accuracy of measurement of the topography of a magnetic field in a beta spectrometer is from 0.02 to 0.005%, respectively. The degree of stabilization is not less than 1 x l0/sup -4/ when the main current in the electromagnet changes plus or minus l%. (auth)
  • Objects smaller than the wavelengths of visible light are a staple of contemporary science and technology. Biologists study single molecules of protein or DNA; materials scientists examine atomic-scale flaws in crystals; microelectronics engineers lay out circuit patterns only a few tens of atoms thick. Until recently this minute world could be seen only by cumbersome, often destructive methods such as electron microscopy and X-ray diffraction. It lay beyond the reach of any instrument as simple and direct as the familiar light microscope. A family of new microscopes opens this realm to direct observation. The devices can map atomic and molecularmore » shapes, electrical, magnetic and mechanical properties and even temperature variations at a higher resolution than ever before, without the need to modify the specimen or expose it to damaging, high-energy radiation. These new microscoped are typified by the scanning tunneling microscoped. In 1956 J.A. O'Keefe, then of the U.S. Army Mapping Service, proposed a microscope in which light would shine through a tiny hole in an opaque screen, illuminating an object directly in front of the screen. Light transmitted through the specimen or reflect back through the hole would be recorded as the sample was scanned back and forth. O'Keefe pointed out that the resolution of such a scanning near-field microscope would be limited only by the size of the hole and not by the wavelength of the light. In principle the device could make superresolving images-images showing details smaller than half a wavelength.« less