Featured Research

from universities, journals, and other organizations

Graphene exhibits bizarre new behavior well suited to electronic devices

Date:
July 30, 2010
Source:
University of California - Berkeley
Summary:
Graphene, a sheet of pure carbon, has been touted as a possible replacement for silicon-based semiconductors because of its useful electronic properties. Now, physicists have shown that graphene has another unique and amazing property that could make it even more suitable for future electronic devices. When contorted in a specific way it sprouts nanobubbles in which electrons behave as if they are moving in a strong magnetic field.

This is a scanning tunneling microscope image of a single layer of graphene on platinum with four nanobubbles at the graphene-platinum border and one in the patch interior. The inset shows a high-resolution image of a graphene nanobubble and its distorted honeycomb lattice due to strain in the bubble.
Credit: Crommie lab, UC Berkeley

Graphene, a sheet of pure carbon heralded as a possible replacement for silicon-based semiconductors, has been found to have a unique and amazing property that could make it even more suitable for future electronic devices.

Physicists at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory (LBNL) have found that when graphene is stretched in a specific way it sprouts nanobubbles in which electrons behave in a bizarre way, as if they are moving in a strong magnetic field.

Specifically, the electrons within each nanobubble segregate into quantized energy levels instead of occupying energy bands, as in unstrained graphene. The energy levels are identical to those that an electron would occupy if it were moving in circles in a very strong magnetic field, as high as 300 tesla, which is bigger than any laboratory can produce except in brief explosions, said Michael Crommie, professor of physics at UC Berkeley and a faculty researcher at LBNL. Magnetic resonance imagers use magnets less than 10 tesla, while the Earth's magnetic field at ground level is 31 microtesla.

"This gives us a new handle on how to control how electrons move in graphene, and thus to control graphene's electronic properties, through strain," Crommie said. "By controlling where the electrons bunch up and at what energy, you could cause them to move more easily or less easily through graphene, in effect, controlling their conductivity, optical or microwave properties. Control of electron movement is the most essential part of any electronic device."

Crommie and colleagues report the discovery in the July 30 issue of the journal Science.

Aside from the engineering implications of the discovery, Crommie is eager to use this unusual property of graphene to explore how electrons behave in fields that until now have been unobtainable in the laboratory.

"When you crank up a magnetic field you start seeing very interesting behavior because the electrons spin in tiny circles," he said. "This effect gives us a new way to induce this behavior, even in the absence of an actual magnetic field."

Among the unusual behaviors observed of electrons in strong magnetic fields are the quantum Hall effect and the fractional quantum Hall effect, where at low temperatures electrons also fall into quantized energy levels.

The new effect was discovered by accident when a UC Berkeley postdoctoral researcher and several students in Crommie's lab grew graphene on the surface of a platinum crystal. Graphene is a one atom-thick sheet of carbon atoms arranged in a hexagonal pattern, like chicken wire. When grown on platinum, the carbon atoms do not perfectly line up with the metal surface's triangular crystal structure, which creates a strain pattern in the graphene as if it were being pulled from three different directions.

The strain produces small, raised triangular graphene bubbles 4 to 10 nanometers across in which the electrons occupy discrete energy levels rather than the broad, continuous range of energies allowed by the band structure of unstrained graphene. This new electronic behavior was detected spectroscopically by scanning tunneling microscopy. These so-called Landau levels are reminiscent of the quantized energy levels of electrons in the simple Bohr model of the atom, Crommie said.

The appearance of a pseudomagnetic field in response to strain in graphene was first predicted for carbon nanotubes in 1997 by Charles Kane and Eugene Mele of the University of Pennsylvania. Nanotubes are a rolled up form of graphene.

Within the last year, however, Francisco Guinea of the Instituto de Ciencia de Materiales de Madrid in Spain, Mikhael Katsnelson of Radboud University of Nijmegen, the Netherlands, and A. K. Geim of the University of Manchester, England predicted what they termed a pseudo quantum Hall effect in strained graphene . This is the very quantization that Crommie's research group has experimentally observed. Boston University physicist Antonio Castro Neto, who was visiting Crommie's laboratory at the time of the discovery, immediately recognized the implications of the data, and subsequent experiments confirmed that it reflected the pseudo quantum Hall effect predicted earlier.

"Theorists often latch onto an idea and explore it theoretically even before the experiments are done, and sometimes they come up with predictions that seem a little crazy at first. What is so exciting now is that we have data that shows these ideas are not so crazy," Crommie said. "The observation of these giant pseudomagnetic fields opens the door to room-temperature 'straintronics,' the idea of using mechanical deformations in graphene to engineer its behavior for different electronic device applications."

Crommie noted that the "pseudomagnetic fields" inside the nanobubbles are so high that the energy levels are separated by hundreds of millivolts, much higher than room temperature. Thus, thermal noise would not interfere with this effect in graphene even at room temperature. The nanobubble experiments performed in Crommie's laboratory, however, were performed at very low temperature.

Normally, electrons moving in a magnetic field circle around the field lines. Within the strained nanobubbles, the electrons move in circles in the plane of the graphene sheet, as if a strong magnetic field has been applied perpendicular to the sheet even when there is no actual magnetic field. Apparently, Crommie said, the pseudomagnetic field only affects moving electrons and not other properties of the electron, such as spin, that are affected by real magnetic fields.

Other authors of the report, in addition to Crommie, Castro Neto and Guinea, are Sarah Burke, now a professor at the University of British Columbia; Niv Levy, now a postdoctoral researcher at the National Institute of Technology and Standards; and graduate student Kacey L. Meaker, undergraduate Melissa Panlasigui and physics professor Alex Zettl of UC Berkeley.

The research was funded through the U.S. Department of Energy Office of Science and the U.S. Office of Naval Research.


Story Source:

The above story is based on materials provided by University of California - Berkeley. Note: Materials may be edited for content and length.


Journal Reference:

  1. N. Levy, S. A. Burke, K. L. Meaker, M. Panlasigui, A. Zettl, F. Guinea, A. H. Castro Neto, and M. F. Crommie. Strain-Induced Pseudo-Magnetic Fields Greater Than 300 Tesla in Graphene Nanobubbles. Science, 30 July 2010: 544-547 DOI: 0.1126/science.1191700

Cite This Page:

University of California - Berkeley. "Graphene exhibits bizarre new behavior well suited to electronic devices." ScienceDaily. ScienceDaily, 30 July 2010. <www.sciencedaily.com/releases/2010/07/100729141134.htm>.
University of California - Berkeley. (2010, July 30). Graphene exhibits bizarre new behavior well suited to electronic devices. ScienceDaily. Retrieved August 22, 2014 from www.sciencedaily.com/releases/2010/07/100729141134.htm
University of California - Berkeley. "Graphene exhibits bizarre new behavior well suited to electronic devices." ScienceDaily. www.sciencedaily.com/releases/2010/07/100729141134.htm (accessed August 22, 2014).

Share This




More Matter & Energy News

Friday, August 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Flower Power! Dandelions Make Car Tires?

Flower Power! Dandelions Make Car Tires?

Reuters - Business Video Online (Aug. 20, 2014) Forget rolling on rubber, could car drivers soon be traveling on tires made from dandelions? Teams of scientists are racing to breed a type of the yellow flower whose taproot has a milky fluid with tire-grade rubber particles in it. As Joanna Partridge reports, global tire makers are investing millions in research into a new tire source. Video provided by Reuters
Powered by NewsLook.com
Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Newsy (Aug. 19, 2014) Scientists have developed a new device that mimics the way octopuses blend in with their surroundings to hide from dangerous predators. Video provided by Newsy
Powered by NewsLook.com
Researcher Testing on-Field Concussion Scanners

Researcher Testing on-Field Concussion Scanners

AP (Aug. 19, 2014) Four Texas high school football programs are trying out an experimental system designed to diagnose concussions on the field. The technology is in response to growing concern over head trauma in America's most watched sport. (Aug. 19) Video provided by AP
Powered by NewsLook.com
Green Power Blooms as Japan Unveils 'hydrangea Solar Cell'

Green Power Blooms as Japan Unveils 'hydrangea Solar Cell'

AFP (Aug. 19, 2014) A solar cell that resembles a flower is offering a new take on green energy in Japan, where one scientist is searching for renewables that look good. Duration: 01:29 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins