Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > Measuring the mass of 'massless' electrons: Taming graphene, Harvard-led researchers successfully measure collective mass of ‘massless’ electrons in motion

A schematic of the experimental setup. Ham and Yoon measured the change in phase of a microwave signal sent through the graphene.Image courtesy of Hosang Yoon, Harvard SEAS.
A schematic of the experimental setup. Ham and Yoon measured the change in phase of a microwave signal sent through the graphene.

Image courtesy of Hosang Yoon, Harvard SEAS.

Abstract:
Individual electrons in graphene are massless, but when they move together, it's a different story.

Graphene, a one-atom-thick carbon sheet, has taken the world of physics by storm—in part, because its electrons behave as massless particles. Yet these electrons seem to have dual personalities. Phenomena observed in the field of graphene plasmonics suggest that when the electrons move collectively, they must exhibit mass.

Measuring the mass of 'massless' electrons: Taming graphene, Harvard-led researchers successfully measure collective mass of ‘massless’ electrons in motion

Cambridge, MA | Posted on June 24th, 2014

After two years of effort, researchers led by Donhee Ham, Gordon McKay Professor of Electrical Engineering and Applied Physics at the Harvard School of Engineering and Applied Sciences (SEAS), and his student Hosang Yoon, Ph.D.'14, have successfully measured the collective mass of ‘massless' electrons in motion in graphene.

By shedding light on the fundamental kinetic properties of electrons in graphene, this research may also provide a basis for the creation of miniaturized circuits with tiny, graphene-based components.

The results of Ham and Yoon's complex measurements, performed in collaboration with other experts at Columbia University and the National Institute for Materials Science in Japan, have been published online in Nature Nanotechnology.

"Graphene is a unique material because, effectively, individual graphene electrons act as though they have no mass. What that means is that the individual electrons always move at a constant velocity," explains Ham. "But suppose we apply a force, like an electric field. The velocity of the individual electrons still remains constant, but collectively, they accelerate and their total energy increases—just like entities with mass. It's quite interesting."

Without this mass, the field of graphene plasmonics cannot work, so Ham's team knew it had to be there—but until now, no one had accurately measured it.

"One of the greatest contributions of this work is that it is actually an extremely difficult measurement," says Ham.

As Newton's second law dictates, a force applied to a mass must generate acceleration. Yoon and Ham knew that if they could apply an electric field to a graphene sample and measure the electrons' resulting collective acceleration, they could then use that data to calculate the collective mass.

But the graphene samples used in past experiments were replete with imperfections and impurities—places where a carbon atom was missing or had been replaced by something different. In those past experiments, electrons would accelerate but very quickly scatter as they collided with the impurities and imperfections.

"The scattering time was so short in those studies that you could never see the acceleration directly," says Ham.

To overcome the scattering problem, several smart changes were necessary.

First, Ham and Yoon joined forces with Philip Kim, a physics professor at Columbia who will join the Harvard faculty on July 1 as Professor of Physics and of Applied Physics. A Harvard graduate (Ph.D. '99), Kim is well known for his pioneering fundamental studies of graphene and his expertise in fabricating high-quality graphene samples. The team was now able to reduce the number of impurities and imperfections by sandwiching the graphene between layers of hexagonal boron nitride, an insulating material with a similar atomic structure. By also collaborating with James Hone, a professor of mechanical engineering at Columbia, they designed a better way to connect electrical signal lines to the sandwiched graphene. And Yoon and Ham applied an electric field at a microwave frequency, which allows for the direct measurement of the electrons' collective acceleration in the form of a phase delay in the current.

"By doing all this, we translated the situation from completely impossible to being at the verge of either seeing the acceleration or not," says Ham. "However, the difficulty was still very daunting, and Hosang [Yoon] made it all possible by performing very fine and subtle microwave engineering and measurements—a formidable piece of experimentation."

"To me, it was a victorious moment that finally justified a long-term effort, going through multiple trials and errors," says Yoon, lead author of the paper in Nature Nanotechnology. "Until then, I wasn't even sure if the experiment would really be possible, so it was like a ‘through darkness comes light' moment."

Collective mass is a key aspect of explaining plasmonic behaviors in graphene. By demonstrating that graphene electrons exhibit a collective mass and by measuring its value accurately, Yoon says, "We think it will help people to understand and design more sophisticated plasmonic devices with graphene."

The team's experiments also revealed that, in graphene, kinetic inductance (the electrical manifestation of collective mass) is several orders of magnitude larger than another, far more commonly exploited property called magnetic inductance. This is important in the push toward smaller and smaller electronic circuitry—the main theme of modern integrated circuits—because it means the same level of inductance can be achieved in a far smaller area. Furthermore, Ham and Yoon say that this miniature graphene-based kinetic inductor could enable the creation of a solid-state voltage-controlled inductor, complementary to the widely used voltage-controlled capacitor. It could be used to substantially increase the frequency tuning range of electronic circuits, which is an important function in communication applications.

For now, the challenge remains to improve the quality of graphene samples so that the detrimental effects of electron scattering can be further reduced.

##

Hosang Yoon is lead author of the paper in Nature Nanotechnology, with corresponding authors Donhee Ham at Harvard SEAS and Philip Kim at Columbia. Additional coauthors include Columbia professor James Hone, Columbia graduate students Carlos Forsythe and Lei Wang; Nikolaos Tombros, a former member of the Kim lab at Columbia, now at the University of Groningen in the Netherlands; Kenji Watanabe, chief researchers in optoelectronic materials at the National Institute for Materials Science (NIMS) in Japan; and Takashi Taniguchi, group leader in the Ultra-high Pressure Processes Group at NIMS.

This research was supported by the Air Force Office of Scientific Research, the Office of Naval Research, the National Science Foundation, and the Samsung Advanced Institute of Technology and its Global Research Opportunity program. Additional support was provided by the Nano Material Technology Development Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT and Future Planning; the Columbia Optics and Quantum Electronics IGERT; and the Netherlands Organisation for Scientific Research.

####

For more information, please click here

Contacts:
Caroline Perry

617-496-1351

Copyright © Harvard 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

News and information

Nano Ruffles in Brain Matter: Freiburg researchers decipher the role of nanostructures around brain cells in central nervous system function October 31st, 2014

Gold nanoparticle chains confine light to the nanoscale October 31st, 2014

'Nanomotor lithography' answers call for affordable, simpler device manufacturing October 31st, 2014

Device invented at Johns Hopkins provides up-close look at cancer on the move: Microscopic view of metastasis could give insight about how to keep cancer in check October 31st, 2014

Amorphous Coordination Polymer Particles as alternative to classical nanoplatforms for nanomedicine October 30th, 2014

Wireless/telecommunications/RF/Antennas

Gold nanoparticle chains confine light to the nanoscale October 31st, 2014

Iranian Scientists Use Nanotechnology to Produce Dielectric Microwave Ceramics October 14th, 2014

Physics

Sussex physicists find simple solution for quantum technology challenge October 28th, 2014

New evidence for an exotic, predicted superconducting state October 27th, 2014

Graphene

Haydale Secures Exclusive Development and Supply Agreement with Tantec A/S: New reactors to be built and commissioned by Tantec A/S represent another step forward towards the commercialisation of graphene October 24th, 2014

Nitrogen Doped Graphene Characterized by Iranian, Russian, German Scientists October 21st, 2014

Graphenea opens US branch October 16th, 2014

Govt.-Legislation/Regulation/Funding/Policy

Gold nanoparticle chains confine light to the nanoscale October 31st, 2014

'Nanomotor lithography' answers call for affordable, simpler device manufacturing October 31st, 2014

Device invented at Johns Hopkins provides up-close look at cancer on the move: Microscopic view of metastasis could give insight about how to keep cancer in check October 31st, 2014

'Electronic skin' could improve early breast cancer detection October 29th, 2014

Discoveries

Nano Ruffles in Brain Matter: Freiburg researchers decipher the role of nanostructures around brain cells in central nervous system function October 31st, 2014

Gold nanoparticle chains confine light to the nanoscale October 31st, 2014

'Nanomotor lithography' answers call for affordable, simpler device manufacturing October 31st, 2014

Device invented at Johns Hopkins provides up-close look at cancer on the move: Microscopic view of metastasis could give insight about how to keep cancer in check October 31st, 2014

Announcements

Nano Ruffles in Brain Matter: Freiburg researchers decipher the role of nanostructures around brain cells in central nervous system function October 31st, 2014

Gold nanoparticle chains confine light to the nanoscale October 31st, 2014

'Nanomotor lithography' answers call for affordable, simpler device manufacturing October 31st, 2014

Device invented at Johns Hopkins provides up-close look at cancer on the move: Microscopic view of metastasis could give insight about how to keep cancer in check October 31st, 2014

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

Nano Ruffles in Brain Matter: Freiburg researchers decipher the role of nanostructures around brain cells in central nervous system function October 31st, 2014

'Nanomotor lithography' answers call for affordable, simpler device manufacturing October 31st, 2014

Device invented at Johns Hopkins provides up-close look at cancer on the move: Microscopic view of metastasis could give insight about how to keep cancer in check October 31st, 2014

Production of Biocompatible Polymers in Iran October 30th, 2014

Military

'Nanomotor lithography' answers call for affordable, simpler device manufacturing October 31st, 2014

Microrockets fueled by water neutralize chemical and biological warfare agents October 29th, 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

NanoTechnology for Defense (NT4D) October 22nd, 2014

Research partnerships

Nano Ruffles in Brain Matter: Freiburg researchers decipher the role of nanostructures around brain cells in central nervous system function October 31st, 2014

First Observation of Electronic Structure in Ag-Rh Alloy Nanoparticles Having Hydrogen Absorbing: Storage Property –Attempting to solve the mystery of why Ag-Rh alloy nanoparticles have a similar property to Pd– October 30th, 2014

Sussex physicists find simple solution for quantum technology challenge October 28th, 2014

New evidence for an exotic, predicted superconducting state October 27th, 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