Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Experiments bolster theory of how electrons cool in graphene

Matt Graham
An illustration of how a heated electron cools in graphene. The electron slowly cools by emitting regular phonons, illustrated by zigzags down a Dirac Cone (a visualization of graphene's electronic band structure). When the electron hits a defect, it bounces off the lattice - a "supercollision" - which speeds up the cooling process.
Matt Graham

An illustration of how a heated electron cools in graphene. The electron slowly cools by emitting regular phonons, illustrated by zigzags down a Dirac Cone (a visualization of graphene's electronic band structure). When the electron hits a defect, it bounces off the lattice - a "supercollision" - which speeds up the cooling process.

Abstract:
It's a basic tenet of physics that scientists are trying to explain in graphene, single-atom thick sheets of carbon: When electrons are excited, or heated, how quickly do they relax, or cool?

Experiments bolster theory of how electrons cool in graphene

Ithaca, NY | Posted on December 3rd, 2012

A research team supported by the Kavli Institute at Cornell for Nanoscale Science has shed some light on the topic through the first known direct measurements of hot electrons cooling down in graphene.

The team, which published its findings online Dec. 2 in the journal Nature Physics, includes lead researcher Paul McEuen, the Kavli Institute director and Goldwin Smith Professor of Physics; first author Matt Graham, a Kavli postdoctoral fellow; and co-authors Jiwoong Park, assistant professor of chemistry and chemical biology and Kavli member; Dan Ralph, Horace White Professor of Physics and Kavli member; and Su-Fei Shen, Ralph's former graduate student.

When electrons travel through graphene, they create a quantum lattice vibration, called a phonon. In doing so, the difference in energy the electron emits must equal the amount gained by the phonon; this is the "cooling" that happens as the system is returning to its equilibrium state, and this movement of electrons is at the heart of understanding how electronic devices work.

The new Cornell experiment supports a previous theory that electrons in graphene experience "supercollisions" as they cool -- they bump into defects in the crystal lattice, imparting their momentum to the defects, thereby making the cooling process much faster than if the graphene were a perfectly repeating crystal.

"The remarkable thing about the theory was it predicted all kinds of details, and it got it all right," McEuen said.

Watching electrons move through graphene took some novel experimental legwork. Graham and colleagues conceived a setup in which they shot very short laser pulses -- about 100 femtoseconds apart -- at a piece of conventionally grown graphene.

They observed the temperature of the graphene as it heated and cooled at a p-n junction, which is the interface at which electrons travel between two semiconductors. By tracking the magnitude of the current passing through the junction, they essentially used the junction as a tiny thermometer.

Heating the junction with an initial laser pulse, they hit it with a second pulse at specific time delays, comparing the crossover of temperatures. This technique allowed the team to measure the temperature of the system with sub-picosecond time resolution and within a few kelvins of accuracy. Their results agreed very well with the supercollision theory of the rate at which electrons cool in graphene.

The results provide further insights into the fundamental nature of graphene so it can one day be used in anything from photodetectors to non-silicon transistors, McEuen said. It is already well known that graphene shows promise for next-generation electronics because of its near-perfect conductivity, transparency and tensile strength.

The work was supported by the Kavli Institute, the National Science Foundation through the Center for Nanoscale Systems, the MARCO Focused Research Center on Materials, Structures and Devices, and the Air Force Office of Scientific Research.

####

For more information, please click here

Contacts:
Media Contact:
Syl Kacapyr
(607) 255-7701


Cornell Chronicle:
Anne Ju
(607) 255-9735

Copyright © Cornell University

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

Physics

Scientists create antilaser for ultracold atoms condensate August 16th, 2018

How hot is Schrödinger's coffee? August 15th, 2018

Yale-NUS scientist and collaborators solve open theoretical problem on electron interactions August 10th, 2018

Graphene/ Graphite

CTI Materials drives nano commercialization with it's patented surfactant free nanoparticle dispersions August 15th, 2018

Flipping the switch on supramolecular electronics August 14th, 2018

Quantum chains in graphene nanoribbons: Breakthrough in nanoresearch August 9th, 2018

Govt.-Legislation/Regulation/Funding/Policy

UVA multidisciplinary engineering team designs technology for smart materials: The invention could lead to devices and manufactured goods, such as fabrics, that can dynamically regulate between thermally insulating and cooling August 17th, 2018

Scientists turn to the quantum realm to improve energy transportation August 17th, 2018

Research brief: UMN researchers use green gold to rapidly detect and identify harmful bacteria August 15th, 2018

Particles pull last drops of oil from well water: Rice University engineers find nanoscale solution to 'produced water' problem August 15th, 2018

Discoveries

Novel nanoparticle-based approach detects and treats oral plaque without drugs August 17th, 2018

UVA multidisciplinary engineering team designs technology for smart materials: The invention could lead to devices and manufactured goods, such as fabrics, that can dynamically regulate between thermally insulating and cooling August 17th, 2018

Smallest transistor worldwide switches current with a single atom in solid electrolyte: Milestone of energy efficiency in information technology -- Publication in Advanced Materials August 17th, 2018

Scientists turn to the quantum realm to improve energy transportation August 17th, 2018

Announcements

Novel nanoparticle-based approach detects and treats oral plaque without drugs August 17th, 2018

UVA multidisciplinary engineering team designs technology for smart materials: The invention could lead to devices and manufactured goods, such as fabrics, that can dynamically regulate between thermally insulating and cooling August 17th, 2018

Smallest transistor worldwide switches current with a single atom in solid electrolyte: Milestone of energy efficiency in information technology -- Publication in Advanced Materials August 17th, 2018

Scientists turn to the quantum realm to improve energy transportation August 17th, 2018

Military

Biomimetic micro/nanoscale fiber reinforced composites August 10th, 2018

In borophene, boundaries are no barrier: Rice U., Northwestern researchers make and test atom-thick boron's unique domains July 17th, 2018

UMBC researchers develop nanoparticles to reduce internal bleeding caused by blast trauma July 13th, 2018

Carbon is the new black: Researchers use carbon nanotubes to develop clothing that can double as batteries July 10th, 2018

Grants/Sponsored Research/Awards/Scholarships/Gifts/Contests/Honors/Records

Scientists turn to the quantum realm to improve energy transportation August 17th, 2018

Research brief: UMN researchers use green gold to rapidly detect and identify harmful bacteria August 15th, 2018

Particles pull last drops of oil from well water: Rice University engineers find nanoscale solution to 'produced water' problem August 15th, 2018

Breaking down the Wiedemann-Franz law: In a study exploring the coupling between heat and particle currents in a gas of strongly interacting atoms, physicists at ETH Zurich find puzzling behaviours August 10th, 2018

Photonics/Optics/Lasers

Scientists create antilaser for ultracold atoms condensate August 16th, 2018

Breaking down the Wiedemann-Franz law: In a study exploring the coupling between heat and particle currents in a gas of strongly interacting atoms, physicists at ETH Zurich find puzzling behaviours August 10th, 2018

Optical fibers that can 'feel' the materials around them August 7th, 2018

NUST MISIS scientists present metamaterial for solar cells and nanooptics July 23rd, 2018

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



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project