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

Graphene/ Graphite

New quantum phenomena in graphene superlattices September 18th, 2017

Graphene based terahertz absorbers: Printable graphene inks enable ultrafast lasers in the terahertz range September 13th, 2017

UConn chemist synthesizes pure graphene August 30th, 2017

Physics

New quantum phenomena in graphene superlattices September 18th, 2017

Bit data goes anti-skyrmions September 1st, 2017

Govt.-Legislation/Regulation/Funding/Policy

DNA triggers shape-shifting in hydrogels, opening a new way to make 'soft robots' September 21st, 2017

Copper catalyst yields high efficiency CO2-to-fuels conversion: Berkeley Lab scientists discover critical role of nanoparticle transformation September 20th, 2017

Solar-to-fuel system recycles CO2 to make ethanol and ethylene: Berkeley Lab advance is first demonstration of efficient, light-powered production of fuel via artificial photosynthesis September 19th, 2017

New insights into nanocrystal growth in liquid: Understanding process that creates complex crystals important for energy applications September 14th, 2017

Discoveries

Application of air-sensitive semiconductors in nanoelectronics: 2-D semiconductor gallium selenide in encapsulated nanoelectronic devices September 22nd, 2017

Researchers set time limit for ultrafast perovskite solar cells September 22nd, 2017

DNA triggers shape-shifting in hydrogels, opening a new way to make 'soft robots' September 21st, 2017

Physicists develop new recipes for design of fast single-photon gun Physicists develop high-speed single-photon sources for quantum computers of the future September 21st, 2017

Announcements

Application of air-sensitive semiconductors in nanoelectronics: 2-D semiconductor gallium selenide in encapsulated nanoelectronic devices September 22nd, 2017

Researchers set time limit for ultrafast perovskite solar cells September 22nd, 2017

DNA triggers shape-shifting in hydrogels, opening a new way to make 'soft robots' September 21st, 2017

Physicists develop new recipes for design of fast single-photon gun Physicists develop high-speed single-photon sources for quantum computers of the future September 21st, 2017

Military

DNA triggers shape-shifting in hydrogels, opening a new way to make 'soft robots' September 21st, 2017

First on-chip nanoscale optical quantum memory developed: Smallest-yet optical quantum memory device is a storage medium for optical quantum networks with the potential to be scaled up for commercial use September 11th, 2017

Freeze-dried foam soaks up carbon dioxide: Rice University scientists lead effort to make novel 3-D material August 16th, 2017

2-faced 2-D material is a first at Rice: Rice University materials scientists create flat sandwich of sulfur, molybdenum and selenium August 14th, 2017

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

Magnetic cellular 'Legos' for the regenerative medicine of the future September 12th, 2017

Quantum detectives in the hunt for the world's first quantum computer September 8th, 2017

New results reveal high tunability of 2-D material: Berkeley Lab-led team also provides most precise band gap measurement yet for hotly studied monolayer moly sulfide August 26th, 2017

A more complete picture of the nano world August 24th, 2017

Photonics/Optics/Lasers

Application of air-sensitive semiconductors in nanoelectronics: 2-D semiconductor gallium selenide in encapsulated nanoelectronic devices September 22nd, 2017

Physicists develop new recipes for design of fast single-photon gun Physicists develop high-speed single-photon sources for quantum computers of the future September 21st, 2017

A new approach to ultrafast light pulses: Unusual fluorescent materials could be used for rapid light-based communications systems September 19th, 2017

Graphene based terahertz absorbers: Printable graphene inks enable ultrafast lasers in the terahertz range September 13th, 2017

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