Nanotechnology Now







Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > Light pulses control graphene's electrical behavior: Finding could allow ultrafast switching of conduction, and possibly lead to new broadband light sensors

Researchers at MIT have found a way to control how graphene conducts electricity by using extremely short light pulses. In this illustration, a lattice of graphene is shown with its bonds (bars) connecting carbon atoms (balls). When the light pulse hits the atoms, electrons can accumulate or diminish in number. By controlling the concentration of electrons in a graphene sheet, researchers can change the material's electrical conductivity.

Illustration: Jose-Luis Olivares/MIT
Researchers at MIT have found a way to control how graphene conducts electricity by using extremely short light pulses. In this illustration, a lattice of graphene is shown with its bonds (bars) connecting carbon atoms (balls). When the light pulse hits the atoms, electrons can accumulate or diminish in number. By controlling the concentration of electrons in a graphene sheet, researchers can change the material's electrical conductivity.

Illustration: Jose-Luis Olivares/MIT

Abstract:
Graphene, an ultrathin form of carbon with exceptional electrical, optical, and mechanical properties, has become a focus of research on a variety of potential uses. Now researchers at MIT have found a way to control how the material conducts electricity by using extremely short light pulses, which could enable its use as a broadband light detector.

Light pulses control graphene's electrical behavior: Finding could allow ultrafast switching of conduction, and possibly lead to new broadband light sensors

Cambridge, MA | Posted on August 1st, 2014

The new findings are published in the journal Physical Review Letters, in a paper by graduate student Alex Frenzel, Nuh Gedik, and three others.

The researchers found that by controlling the concentration of electrons in a graphene sheet, they could change the way the material responds to a short but intense light pulse. If the graphene sheet starts out with low electron concentration, the pulse increases the material's electrical conductivity. This behavior is similar to that of traditional semiconductors, such as silicon and germanium.

But if the graphene starts out with high electron concentration, the pulse decreases its conductivity — the same way that a metal usually behaves. Therefore, by modulating graphene's electron concentration, the researchers found that they could effectively alter graphene's photoconductive properties from semiconductorlike to metallike.

The finding also explains the photoresponse of graphene reported previously by different research groups, which studied graphene samples with differing concentration of electrons. "We were able to tune the number of electrons in graphene, and get either response," Frenzel says.

To perform this study, the team deposited graphene on top of an insulating layer with a thin metallic film beneath it; by applying a voltage between graphene and the bottom electrode, the electron concentration of graphene could be tuned. The researchers then illuminated graphene with a strong light pulse and measured the change of electrical conduction by assessing the transmission of a second, low-frequency light pulse.

In this case, the laser performs dual functions. "We use two different light pulses: one to modify the material, and one to measure the electrical conduction," Gedik says, adding that the pulses used to measure the conduction are much lower frequency than the pulses used to modify the material behavior. To accomplish this, the researchers developed a device that was transparent, Frenzel explains, to allow laser pulses to pass through it.

This all-optical method avoids the need for adding extra electrical contacts to the graphene. Gedik, the Lawrence C. and Sarah W. Biedenharn Associate Professor of Physics, says the measurement method that Frenzel implemented is a "cool technique. Normally, to measure conductivity you have to put leads on it," he says. This approach, by contrast, "has no contact at all."

Additionally, the short light pulses allow the researchers to change and reveal graphene's electrical response in only a trillionth of a second.

In a surprising finding, the team discovered that part of the conductivity reduction at high electron concentration stems from a unique characteristic of graphene: Its electrons travel at a constant speed, similar to photons, which causes the conductivity to decrease when the electron temperature increases under the illumination of the laser pulse. "Our experiment reveals that the cause of photoconductivity in graphene is very different from that in a normal metal or semiconductor," Frenzel says.

The researchers say the work could aid the development of new light detectors with ultrafast response times and high sensitivity across a wide range of light frequencies, from the infrared to ultraviolet. While the material is sensitive to a broad range of frequencies, the actual percentage of light absorbed is small. Practical application of such a detector would therefore require increasing absorption efficiency, such as by using multiple layers of graphene, Gedik says.

###

The research team also included Jing Kong, the ITT Career Development Associate Professor of Electrical Engineering at MIT, who provided the graphene samples used for the experiments; physics postdoc Chun Hung Lui; and Yong Cheol Shin, a graduate student in materials science and engineering. The work received support from the U.S. Department of Energy and the National Science Foundation.

####

For more information, please click here

Contacts:
Andrew Carleen

617-253-1682

Copyright © Massachusetts 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

When mediated by superconductivity, light pushes matter million times more April 28th, 2015

Chemists strike nano-gold: 4 new atomic structures for gold nanoparticle clusters: Research builds upon work by Nobel Prize-winning team from Stanford University April 28th, 2015

More is less in novel electronic material: Adding electrons actually shrinks the system April 27th, 2015

Two-dimensional semiconductor comes clean April 27th, 2015

Scientists join forces to reveal the mass and shape of single molecules April 27th, 2015

Graphene

Two-dimensional semiconductor comes clean April 27th, 2015

The 16th Trends in Nanotechnology International Conference (TNT 2015) unveils 25 Keynote Speakers: Call for abstracts open April 27th, 2015

Wireless/telecommunications/RF/Antennas

Scientists create invisible objects without metamaterial cloaking April 14th, 2015

A glass fiber that brings light to a standstill: By coupling photons to atoms, light in a glass fiber can be slowed down to the speed of an express train; for a short while it can even be brought to a complete stop April 9th, 2015

New understanding of electromagnetism could enable 'antennas on a chip' April 9th, 2015

Demonstration of 50GHz Ge Waveguide Electro-Absorption Modulator April 2nd, 2015

Govt.-Legislation/Regulation/Funding/Policy

Chemists strike nano-gold: 4 new atomic structures for gold nanoparticle clusters: Research builds upon work by Nobel Prize-winning team from Stanford University April 28th, 2015

International research team discovers new mechanism behind malaria progression: Findings provide a new avenue for research in malaria treatment April 27th, 2015

More is less in novel electronic material: Adding electrons actually shrinks the system April 27th, 2015

Two-dimensional semiconductor comes clean April 27th, 2015

Sensors

Sensor Designed in Iran Able to Remove Formaldehyde Gas from Environment April 27th, 2015

ORNL reports method that takes quantum sensing to new level April 23rd, 2015

New class of 3D-printed aerogels improve energy storage April 22nd, 2015

‘Oxford Instruments Young Nanoscientist India Award 2015’ to Prof. Arindam Ghosh April 20th, 2015

Discoveries

When mediated by superconductivity, light pushes matter million times more April 28th, 2015

Chemists strike nano-gold: 4 new atomic structures for gold nanoparticle clusters: Research builds upon work by Nobel Prize-winning team from Stanford University April 28th, 2015

Scientists join forces to reveal the mass and shape of single molecules April 27th, 2015

Sensor Designed in Iran Able to Remove Formaldehyde Gas from Environment April 27th, 2015

Materials/Metamaterials

More is less in novel electronic material: Adding electrons actually shrinks the system April 27th, 2015

The 16th Trends in Nanotechnology International Conference (TNT 2015) unveils 25 Keynote Speakers: Call for abstracts open April 27th, 2015

Graphenea celebrates fifth anniversary April 27th, 2015

Surface matters: Huge reduction of heat conduction observed in flat silicon channels April 23rd, 2015

Announcements

When mediated by superconductivity, light pushes matter million times more April 28th, 2015

Chemists strike nano-gold: 4 new atomic structures for gold nanoparticle clusters: Research builds upon work by Nobel Prize-winning team from Stanford University April 28th, 2015

Graphenea celebrates fifth anniversary April 27th, 2015

Sensor Designed in Iran Able to Remove Formaldehyde Gas from Environment April 27th, 2015

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers

When mediated by superconductivity, light pushes matter million times more April 28th, 2015

Two-dimensional semiconductor comes clean April 27th, 2015

Scientists join forces to reveal the mass and shape of single molecules April 27th, 2015

Sensor Designed in Iran Able to Remove Formaldehyde Gas from Environment April 27th, 2015

Photonics/Optics/Lasers

When mediated by superconductivity, light pushes matter million times more April 28th, 2015

Northwestern scientists develop first liquid nanolaser: Technology could lead to new way of doing 'lab on a chip' medical diagnostics April 25th, 2015

Fast and accurate 3-D imaging technique to track optically trapped particles April 24th, 2015

ORNL reports method that takes quantum sensing to new level April 23rd, 2015

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