Nanotechnology Now

Our NanoNews Digest Sponsors



Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > Electron orbits in multilayer graphene find energy gaps

Graphene Electron Motion
Graphene Electron Motion

Abstract:
Researchers have taken one more step toward understanding the unique and often unexpected properties of graphene, a two-dimensional carbon material that has attracted interest because of its potential applications in future generations of electronic devices.

By John Toon

Electron orbits in multilayer graphene find energy gaps

Atlanta, GA | Posted on August 10th, 2010

In the Aug. 8 advance online edition of the journal Nature Physics, researchers from the Georgia Institute of Technology and the National Institute of Standards and Technology (NIST) describe for the first time how the orbits of electrons are distributed spatially by magnetic fields applied to layers of epitaxial graphene.

The research team also found that these electron orbits can interact with the substrate on which the graphene is grown, creating energy gaps that affect how electron waves move through the multilayer material. These energy gaps could have implications for the designers of certain graphene-based electronic devices.

"The regular pattern of energy gaps in the graphene surface creates regions where electron transport is not allowed," said Phillip N. First, a professor in the Georgia Tech School of Physics and one of the paper's co-authors. "Electron waves would have to go around these regions, requiring new patterns of electron wave interference. Understanding such interference will be important for bi-layer graphene devices that have been proposed, and may be important for other lattice-matched substrates used to support graphene and graphene devices."

In a magnetic field, an electron moves in a circular trajectory -- known as a cyclotron orbit -- whose radius depends on the size of the magnetic field and the energy of electron. For a constant magnetic field, that's a little like rolling a marble around in a large bowl, First said.

"At high energy, the marble orbits high in the bowl, while for lower energies, the orbit size is smaller and lower in the bowl," he explained. "The cyclotron orbits in graphene also depend on the electron energy and the local electron potential -- corresponding to the bowl -- but until now, the orbits hadn't been imaged directly."

Placed in a magnetic field, these orbits normally drift along lines of nearly constant electric potential. But when a graphene sample has small fluctuations in the potential, these "drift states" can become trapped at a hill or valley in the material that has closed constant potential contours. Such trapping of charge carriers is important for the quantum Hall effect, in which precisely quantized resistance results from charge conduction solely through the orbits that skip along the edges of the material.

The study focused on one particular electron orbit: a zero-energy orbit that is unique to graphene. Because electrons are matter waves, interference within a material affects how their energy relates to the velocity of the wave -- and reflected waves added to an incoming wave can combine to produce a slower composite wave. Electrons moving through the unique "chicken-wire" arrangement of carbon-carbon bonds in the graphene interfere in a way that leaves the wave velocity the same for all energy levels.

In addition to finding that energy states follow contours of constant electric potential, the researchers discovered specific areas on the graphene surface where the orbital energy of the electrons changes from one atom to the next. That creates an energy gap within isolated patches on the surface.

"By examining their distribution over the surface for different magnetic fields, we determined that the energy gap is due to a subtle interaction with the substrate, which consists of multilayer graphene grown on a silicon carbide wafer," First explained.

In multilayer epitaxial graphene, each layer's symmetrical sublattice is rotated slightly with respect to the next. In prior studies, researchers found that the rotations served to decouple the electronic properties of each graphene layer.

"Our findings hold the first indications of a small position-dependent interaction between the layers," said David L. Miller, the paper's first author and a graduate student in First's laboratory. "This interaction occurs only when the size of a cyclotron orbit -- which shrinks as the magnetic field is increased -- becomes smaller than the size of the observed patches."

The origin of the position dependent interaction is believed to be the "moiré pattern" of atomic alignments between two adjacent layers of graphene. In some regions, atoms of one layer lie atop atoms of the layer below, while in other regions, none of the atoms align with the atoms in the layer below. In still other regions, half of the atoms have neighbors in the underlayer, an instance in which the symmetry of the carbon atoms is broken and the Landau level -- discrete energy level of the electrons -- splits into two different energies.

Experimentally, the researchers examined a sample of epitaxial graphene grown at Georgia Tech in the laboratory of Professor Walt de Heer, using techniques developed by his research team over the past several years.

They used the tip of a custom-built scanning-tunneling microscope (STM) to probe the atomic-scale electronic structure of the graphene in a technique known as scanning tunneling spectroscopy. The tip was moved across the surface of a 100-square nanometer section of graphene, and spectroscopic data was acquired every 0.4 nanometers.

The measurements were done at 4.3 degrees Kelvin to take advantage of the fact that energy resolution is proportional to the temperature. The scanning-tunneling microscope, designed and built by Joseph Stroscio at NIST's Center for Nanoscale Science and Technology, used a superconducting magnet to provide the magnetic fields needed to study the orbits.

According to First, the study raises a number of questions for future research, including how the energy gaps will affect electron transport properties, how the observed effects may impact proposed bi-layer graphene coherent devices -- and whether the new phenomenon can be controlled.

"This study is really a stepping stone in long path to understanding the subtleties of graphene's interesting properties," he said. "This material is different from anything we have worked with before in electronics."

In addition to those already mentioned, the study also included Walt de Heer, Kevin D. Kubista, Ming Ruan, and Markus Kinderman from Georgia Tech and Gregory M. Rutter from NIST. The research was supported by the National Science Foundation, the Semiconductor Research Corporation and the W.M. Keck Foundation. Additional assistance was provided by Georgia Tech's Materials Research Science and Engineering Center (MRSEC).

####

For more information, please click here

Contacts:
Media Relations Contacts:
John Toon
404-894-6986


Abby Vogel Robinson
404-385-3364

Copyright © Georgia Institute of Technology

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

NMTI announces breakthrough solutions for HAMR nanoantenna for next-generation ultra-high density magnetic storage November 21st, 2014

Leica Microsystems Presents Universal Hybrid Detector for Single Molecule Detection and Imaging at SfN and ASCB: Leica HyD SMD - the Optimal Detector for Precise and Reliable SMD data November 20th, 2014

Silver Nanoparticles Produced in Iran from Forest Plants Extract November 20th, 2014

Nano Sorbents Able to Remove Pollutions Caused by Oil Derivatives November 20th, 2014

Govt.-Legislation/Regulation/Funding/Policy

NMTI announces breakthrough solutions for HAMR nanoantenna for next-generation ultra-high density magnetic storage November 21st, 2014

Sustainable Nanotechnologies Project November 20th, 2014

Quantum mechanical calculations reveal the hidden states of enzyme active sites November 20th, 2014

NRL Scientists Discover Novel Metamaterial Properties within Hexagonal Boron Nitride November 20th, 2014

Possible Futures

A novel method for identifying the body’s ‘noisiest’ networks November 19th, 2014

Researchers discern the shapes of high-order Brownian motions November 17th, 2014

VDMA Electronics Production Equipment: Growth track for 2014 and 2015 confirmed: Business climate survey shows robust industry sector November 14th, 2014

Open Materials Development Will Be Key for HP's Success in 3D Printing: HP can make a big splash in 3D printing, but it needs to shore up technology claims and avoid the temptation of the razor/razor blade business model in order to flourish November 11th, 2014

Academic/Education

SUNY Poly Student Awarded Fellowship with the U.S. Department of Energy's Postgraduate Research Program: Ph.D. Candidate Accepts Postmaster's Appointment To Conduct Research At Albany NanoTech Complex November 13th, 2014

SUNY Polytechnic Institute Hosts Massive Crowd of More Than 3,000 People Who Attended Community Day Activities Across New York State: CNSE’s ‘NANOvember’ kickoff event highlights New York State’s growing high-tech sector with open house events in Albany, Utica, and Rochester November 3rd, 2014

SUNY Polytechnic Institute Invites the Public to Attend its Popular Statewide 'NANOvember' Series of Outreach and Educational Events October 23rd, 2014

First Canada Excellence Research Chair gets $10 million from the federal government for oilsands research at the University of Calgary: Federal government announces prestigious research chair to study improving oil production efficiency October 19th, 2014

Nanotubes/Buckyballs

Tesla NanoCoatings Increasing Use of SouthWest NanoTechnologies Carbon Nanotubes (CNTs) for its Infrastructure Coatings and Paints: High Quality SMW™ Specialty Multi-wall Carbon Nanotubes Incorporated into Teslan®-brand coatings used by Transportation, Oil and Gas Companies November 19th, 2014

Graphene/nanotube hybrid benefits flexible solar cells: Rice University labs create novel electrode for dye-sensitized cells November 17th, 2014

SouthWest NanoTechnologies to Demonstrate 3D Capacitive Touch Sensor Featuring Transparent, Thermoformed Carbon Nanotube Ink at Printed Electronics USA 2014 (Booth J25) -- “Conductive and Semiconducting Single-Wall Carbon Nanotube Inks” will be Topic of Company Presentation November 10th, 2014

Neural Canals Produced in Iran for Recovery of Sciatica Nerve November 8th, 2014

Nanoelectronics

Leti Will Present 17 Papers at 2014 IEDM; the Highest-ever Total Includes Four Invited Papers: Institute also Will Present its Latest Results in Key Technologies and Its Roadmap for Silicon Nano-technologies at Workshop November 13th, 2014

Breakthrough in molecular electronics paves the way for DNA-based computer circuits in the future: DNA-based programmable circuits could be more sophisticated, cheaper and simpler to make October 27th, 2014

NIST offers electronics industry 2 ways to snoop on self-organizing molecules October 22nd, 2014

Materials for the next generation of electronics and photovoltaics: MacArthur Fellow develops new uses for carbon nanotubes October 21st, 2014

Announcements

NMTI announces breakthrough solutions for HAMR nanoantenna for next-generation ultra-high density magnetic storage November 21st, 2014

Leica Microsystems Presents Universal Hybrid Detector for Single Molecule Detection and Imaging at SfN and ASCB: Leica HyD SMD - the Optimal Detector for Precise and Reliable SMD data November 20th, 2014

Silver Nanoparticles Produced in Iran from Forest Plants Extract November 20th, 2014

Nano Sorbents Able to Remove Pollutions Caused by Oil Derivatives November 20th, 2014

Tools

Leica Microsystems Presents Universal Hybrid Detector for Single Molecule Detection and Imaging at SfN and ASCB: Leica HyD SMD - the Optimal Detector for Precise and Reliable SMD data November 20th, 2014

Nanometrics Announces Upcoming Investor Events November 19th, 2014

Two sensors in one: Nanoparticles that enable both MRI and fluorescent imaging could monitor cancer, other diseases November 18th, 2014

Field-emission plug-and-play solution for microwave electron guns: To simplify the electron emission mechanism involved in microwave electron guns, a team of researchers has created and demonstrated a field-emission plug-and-play solution based on ultrananocrystalline diamond November 18th, 2014

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More












ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE