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The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
  • 2017-11-30 11:05:55
  • Article ID: 685970

Craters on Graphene: Electrons Impact

Novel defect control in graphene enables direct imaging of trapped electrons that follow Einstein's rules.

  • Credit: Image courtesy of Lawrence Berkeley National Laboratory

    Trapped electrons that follow the rules of relativistic quantum mechanics were directly imaged, validating theoretical predictions that these electrons traveling at near the speed of light can tunnel through energy barriers. The map shows the circular interference patterns of a graphene quantum dot, where the standing wave near the center of the dot arises from confined electronic states. This 300- by 300-nanometer map, representing a region that is a fraction of the size of the head of a pin, was obtained with a scanning tunneling microscope. The contrast corresponds to differences in conductance.

The Science

Imaging electrons can help scientists better understand exotic electronic states, such as electricity that travels through wires without loss. The team created images of superfast electrons trapped as they tunnel through energy barriers in graphene. They visualized this unusual tunneling for the first time. They did it by imaging the density of charge carriers in a circular junction in a graphene layer on top of insulating boron nitride. Charge carriers are excited electrons and their holes (positively charged spots where the electrons resided before becoming excited).

The Impact

With this new knowledge of electron physics, we better understand how energy moves through graphene. Controlling electrons’ behavior could open the door for new graphene-based devices. These devices could enable faster, higher performing computers and sensors.

Summary

Normally, electrons moving in a conductor are reflected by potential energy barriers. However, electrons moving in graphene travel at relativistic velocities (near the speed of light) and behave very differently. Theory predicts that some of these electrons will be unaffected by the potential barrier and tunnel directly through it. In a particular type of tunneling called Klein tunneling, particles can burrow through potential barriers with perfect transmission. In pristine graphene, this allows high mobility electronic transport but hinders electrostatic confinement of charge carriers necessary for practical applications. Scientists predicted that circular graphene junctions could trap electrons for short periods of time, resulting in the formation of graphene quantum dots. The researchers made these quantum dots by a novel scanning tunneling microscopy technique that manipulates the local defect charge within an insulating boron nitride substrate by electrostatic gating. Nanoscale graphene junctions were thus created, probed, and imaged. Images validated theoretical predictions and demonstrated that graphene charge carriers could be electrostatically confined by artificial potentials. This work provides a new experimental platform for understanding and controlling the spatial behavior of charge carriers in graphene.

Funding

This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (scanning tunneling microscopy measurement and instrumentation) including work at the Molecular Foundry (graphene characterization), a DOE Office of Science user facility; National Science Foundation (device fabrication, image analysis, and modeling); and National Defense Science & Engineering Graduate Fellowship Program (graduate fellowship).

Publication

J. Lee, D. Wong, J. Velasco Jr., J.F. Rodriguez-Nieva, S. Kahn, H.Z. Tsai, T. Taniguchi, K. Watanabe, A. Zettl, F. Wang, L.S. Levitov, and M.F. Crommie, “Imaging electrostatically confined Dirac fermions in graphene quantum dots.” Nature Physics 12,1032 (2016). [DOI: 10.1038/NPHYS3805]

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The Wet Road to Fast and Stable Batteries

An international team of scientists --- including several researchers from the U.S. Department of Energy's (DOE) Argonne National Laboratory -- - has discovered an anode battery material with superfast charging and stable operation over many thousands of cycles.

Light Perfects Interfaces

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Advance in Light Filtering Technology Has Implications for LCD Screens, Lasers and Beyond

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Scientists Discover Path to Improving Game-Changing Battery Electrode

Researchers from Stanford University, two Department of Energy national labs and the battery manufacturer Samsung created a comprehensive picture of how the same chemical processes that give cathodes their high capacity are also linked to changes in atomic structure that sap performance.

ESnet's Petascale DTN Project Speeds up Data Transfers between Leading HPC Centers

A new Petascale Data Transfer Node project aims to to achieve regular disk-to-disk, end-to-end transfer rates of one petabyte per week between major supercomputing facilities, which translates to achievable throughput rates of about 15 Gbps on real world science data sets.

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Scientists reduce uncertainties in future climate prediction by directly coupling an energy-economy model to an Earth system model.

How Grasslands Regulate Their Productivity in Response to Droughts

Scientists show that grasslands are more sensitive to changes in the amount of moisture in the air than to changes in precipitation.


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NAU Researchers Join DOE Project to Study the Soil Microbiome and Its Effect on Carbon Persistence

NAU Regents' Professor Bruce Hungate, director of the Center for Ecosystem Science and Society (Ecoss), recently joined a new initiative lead by LLNL to study how the soil microbiome controls the mechanisms that regulate the stabilization of the organic matter in soil.

Four Scientists Win the Los Alamos Medal

Los Alamos National Laboratory will award four former researchers with the Los Alamos Medal for their scientific contributions.

Stewart Prager Honored with FPA Distinguished Career Award

Announcement of Fusion Power Associates career award for Stewart Prager

WVU Physicists Among Collaborators Granted $7 Million to Form U.S. Department of Energy Center of Excellence

Scientists pause each afternoon at Kirtland Air Force Base in Sandia National Laboratories in Albuquerque, New Mexico, awaiting the daily lightning flash and unmistakable floor jolt that accompanies a Z shot

US Dept. Of Energy Grant to Advance Combined Heat and Power Systems in the Midwest

The University of Illinois at Chicago has received a five-year, $4.2 million grant from the U.S. Department of Energy to help industrial, commercial, institutional and utility entities evaluate and install highly efficient combined heat and power (CHP) technologies.CHP, also known as cogeneration, is a single system that produces both thermal energy and electricity.

Applications Open: ECS Toyota Young Investigator Fellowship 2018-2019

ECS, in a continued partnership with the Toyota Research Institute of North America (TRINA), a division of Toyota Motor Engineering & Manufacturing North America, Inc. (TEMA), is requesting proposals from young professors and scholars pursuing innovative electrochemical research in green energy technology.

Successful Startup Founder to Lead Entrepreneurship Program at Argonne

John Carlisle has been named the director of Chain Reaction Innovations (CRI), a program aimed at accelerating job creation through innovation, based at the U.S. Department of Energy's Argonne National Laboratory.

Department of Energy Supports Argonne Nuclear Technologies

This fall, U.S. Department of Energy Secretary Rick Perry announced nearly $4.7 million in funding for the department's Argonne National Laboratory across 16 projects in three divisions. Four of those TCF awards, representing more than $1 million in funds, are slated for Argonne's Nuclear Engineering division.

Southern Research Develops Gasifier Technology to Unlock Coal's Potential

Southern Research has been selected to receive nearly $1.7 million in U.S. Department of Energy funding to develop a new, cost-efficient gasifier capable of converting low-grade coal into synthesis gas (syngas) that can be used in a number of applications.

CEBAF Begins Operations following Upgrade Completion

The world's most advanced particle accelerator for investigating the quark structure of matter is gearing up to begin its first experiments following official completion of an upgrade to triple its original design energy. The Continuous Electron Beam Accelerator Facility (CEBAF) at the Department of Energy's Thomas Jefferson National Accelerator Facility is now back online and ramping up for the start of experiments.


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Stirring up a Quantum Spin Liquid with Disorder

New, unexpected paradigm discovered: Disorder may actually promote an exotic quantum state, with potential for ultrafast computing.

Light Perfects Interfaces

Shining light on a growing semiconductor modifies its interface with the surface and could improve the optical properties of each.

Underappreciated Microbes Now Get Credit for Holding Down Two Jobs in Soil

Soil microbes work as both decomposers and synthesizers of carbon compounds in soil, offering new answers with impacts to crops and eco-health.

Energy, Economy, and the Earth: The Benefits of Creating Feedback Loops

Scientists reduce uncertainties in future climate prediction by directly coupling an energy-economy model to an Earth system model.

How Grasslands Regulate Their Productivity in Response to Droughts

Scientists show that grasslands are more sensitive to changes in the amount of moisture in the air than to changes in precipitation.

Building Confidence in Hydrologic Models

Scientists evaluate seven hydrologic models to understand how each model agrees and differs.

El Nino and Liquid Water Clouds Contribute to Antarctic Melt in 2015-2016

Atmospheric Radiation Measurement (ARM) observations provide clues on atmospheric contributions to an Antarctic melt event.

Designer Yeast Consumes Plant Matter and Spits Out Fatty Alcohols for Detergents and Biofuels

Highest concentration and yield of valuable chemicals reported in industrial yeast Saccharomyces cerevisiae.

Making Polymer Chemistry Click

Scientists unlock the key to efficiently make a new class of engineering polymers.

Photosynthesis without Cells: Turning Light into Fuel

An entirely human-made architecture produces hydrogen fuel using light, shows promise for transmitting energy in numerous applications.


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