Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Graphene Under Strain Creates Gigantic Pseudo-Magnetic Fields

A patch of graphene at the surface of a platinum substrate exhibits four triangular nanobubbles at its edges and one in the interior. Scanning tunneling spectroscopy taken at intervals across one nanobubble (inset) shows local electron densities clustering in peaks at discrete Landau-level energies. Pseudo-magnetic fields are strongest at regions of greatest curvature.
A patch of graphene at the surface of a platinum substrate exhibits four triangular nanobubbles at its edges and one in the interior. Scanning tunneling spectroscopy taken at intervals across one nanobubble (inset) shows local electron densities clustering in peaks at discrete Landau-level energies. Pseudo-magnetic fields are strongest at regions of greatest curvature.

Abstract:
Graphene, the extraordinary form of carbon that consists of a single layer of carbon atoms, has produced another in a long list of experimental surprises. In the current issue of the journal Science, a multi-institutional team of researchers headed by Michael Crommie, a faculty senior scientist in the Materials Sciences Division at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and a professor of physics at the University of California at Berkeley, reports the creation of pseudo-magnetic fields far stronger than the strongest magnetic fields ever sustained in a laboratory - just by putting the right kind of strain onto a patch of graphene.

Graphene Under Strain Creates Gigantic Pseudo-Magnetic Fields

Berkeley, CA | Posted on July 30th, 2010

"We have shown experimentally that when graphene is stretched to form nanobubbles on a platinum substrate, electrons behave as if they were subject to magnetic fields in excess of 300 tesla, even though no magnetic field has actually been applied," says Crommie. "This is a completely new physical effect that has no counterpart in any other condensed matter system."

Crommie notes that "for over 100 years people have been sticking materials into magnetic fields to see how the electrons behave, but it's impossible to sustain tremendously strong magnetic fields in a laboratory setting." The current record is 85 tesla for a field that lasts only thousandths of a second. When stronger fields are created, the magnets blow themselves apart.

The ability to make electrons behave as if they were in magnetic fields of 300 tesla or more - just by stretching graphene - offers a new window on a source of important applications and fundamental scientific discoveries going back over a century. This is made possible by graphene's electronic behavior, which is unlike any other material's.

A carbon atom has four valence electrons; in graphene (and in graphite, a stack of graphene layers), three electrons bond in a plane with their neighbors to form a strong hexagonal pattern, like chicken-wire. The fourth electron sticks up out of the plane and is free to hop from one atom to the next. The latter pi-bond electrons act as if they have no mass at all, like photons. They can move at almost one percent of the speed of light.

The idea that a deformation of graphene might lead to the appearance of a pseudo-magnetic field first arose even before graphene sheets had been isolated, in the context of carbon nanotubes (which are simply rolled-up graphene). In early 2010, theorist Francisco Guinea of the Institute of Materials Science of Madrid and his colleagues developed these ideas and predicted that if graphene could be stretched along its three main crystallographic directions, it would effectively act as though it were placed in a uniform magnetic field. This is because strain changes the bond lengths between atoms and affects the way electrons move between them. The pseudo-magnetic field would reveal itself through its effects on electron orbits.

In classical physics, electrons in a magnetic field travel in circles called cyclotron orbits. These were named following Ernest Lawrence's invention of the cyclotron, because cyclotrons continuously accelerate charged particles (protons, in Lawrence's case) in a curving path induced by a strong field.

Viewed quantum mechanically, however, cyclotron orbits become quantized and exhibit discrete energy levels. Called Landau levels, these correspond to energies where constructive interference occurs in an orbiting electron's quantum wave function. The number of electrons occupying each Landau level depends on the strength of the field - the stronger the field, the more energy spacing between Landau levels, and the denser the electron states become at each level - which is a key feature of the predicted pseudo-magnetic fields in graphene.

A serendipitous discovery

Describing their experimental discovery, Crommie says, "We had the benefit of a remarkable stroke of serendipity."

Crommie's research group had been using a scanning tunneling microscope to study graphene monolayers grown on a platinum substrate. A scanning tunneling microscope works by using a sharp needle probe that skims along the surface of a material to measure minute changes in electrical current, revealing the density of electron states at each point in the scan while building an image of the surface.

Crommie was meeting with a visiting theorist from Boston University, Antonio Castro Neto, about a completely different topic when a group member came into his office with the latest data.

"It showed nanobubbles, little pyramid-like protrusions, in a patch of graphene on the platinum surface," Crommie says, "and associated with the graphene nanobubbles there were distinct peaks in the density of electron states."

Crommie says his visitor, Castro Neto, took one look and said, "That looks like the Landau levels predicted for strained graphene."

Sure enough, close examination of the triangular bubbles revealed that their chicken-wire lattice had been stretched precisely along the three axes needed to induce the strain orientation that Guinea and his coworkers had predicted would give rise to pseudo-magnetic fields. The greater the curvature of the bubbles, the greater the strain, and the greater the strength of the pseudo-magnetic field. The increased density of electron states revealed by scanning tunneling spectroscopy corresponded to Landau levels, in some cases indicating giant pseudo-magnetic fields of 300 tesla or more.

"Getting the right strain resulted from a combination of factors," Crommie says. "To grow graphene on the platinum we had exposed the platinum to ethylene" - a simple compound of carbon and hydrogen - "and at high temperature the carbon atoms formed a sheet of graphene whose orientation was determined by the platinum's lattice structure."

To get the highest resolution from the scanning tunneling microscope, the system was then cooled to a few degrees above absolute zero. Both the graphene and the platinum contracted - but the platinum shrank more, with the result that excess graphene pushed up into bubbles, measuring four to 10 nanometers (billionths of a meter) across and from a third to more than two nanometers high.

To confirm that the experimental observations were consistent with theoretical predictions, Castro Neto worked with Guinea to model a nanobubble typical of those found by the Crommie group. The resulting theoretical picture was a near-match to what the experimenters had observed: a strain-induced pseudo-magnetic field some 200 to 400 tesla strong in the regions of greatest strain, for nanobubbles of the correct size.

"Controlling where electrons live and how they move is an essential feature of all electronic devices," says Crommie. "New types of control allow us to create new devices, and so our demonstration of strain engineering in graphene provides an entirely new way for mechanically controlling electronic structure in graphene. The effect is so strong that we could do it at room temperature."

The opportunities for basic science with strain engineering are also huge. For example, in strong pseudo-magnetic fields electrons orbit in tight circles that bump up against one another, potentially leading to novel electron-electron interactions. Says Crommie, "this is the kind of physics that physicists love to explore."

"Strain-induced pseudo-magnetic fields greater than 300 tesla in graphene nanobubbles," by Niv Levy, Sarah Burke, Kacey Meaker, Melissa Panlasigui, Alex Zettl, Francisco Guinea, Antonio Castro Neto, and Michael Crommie, appears in the July 30 issue of Science. The work was supported by the Department of Energy's Office of Science and by the Office of Naval Research.

####

About Lawrence Berkeley National Laboratory
Lawrence Berkeley National Laboratory provides solutions to the world’s most urgent scientific challenges including clean energy, climate change, human health, novel materials, and a better understanding of matter and force in the universe. It is a world leader in improving our lives and knowledge of the world around us through innovative science, advanced computing, and technology that makes a difference. Berkeley Lab is a U.S. Department of Energy (DOE) national laboratory managed by the University of California for the DOE Office of Science.

For more information, please click here

Contacts:
Scientific contact:
Michael Crommie
510-642-9392

Copyright © Lawrence Berkeley National Laboratory

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

Arrowhead Pharmaceuticals to Host R&D Day on Emerging Pipeline of RNAi Therapeutics September 25th, 2018

Arrowhead Pharmaceuticals to Host R&D Day on Emerging Pipeline of RNAi Therapeutics September 25th, 2018

Arrowhead Pharmaceuticals Reports Inducement Grants under NASDAQ Marketplace Rule 5635(c)(4) September 25th, 2018

Viral RNA sensing: Optical detection of picomolar concentrations of RNA using switches in plasmonic chirality September 21st, 2018

UT engineers develop first method for controlling nanomotors: Breakthrough for nanotechnology as UT engineers develop first method for switching the mechanical motion of nanomotors September 21st, 2018

Physics

Searching for errors in the quantum world September 21st, 2018

How a tetrahedral substance can be more symmetrical than a spherical atom: A new type of symmetry September 14th, 2018

Govt.-Legislation/Regulation/Funding/Policy

UT engineers develop first method for controlling nanomotors: Breakthrough for nanotechnology as UT engineers develop first method for switching the mechanical motion of nanomotors September 21st, 2018

Researchers develop microbubble scrubber to destroy dangerous biofilms September 19th, 2018

Researchers managed to prevent the disappearing of quantum information September 14th, 2018

New photonic chip promises more robust quantum computers September 14th, 2018

Possible Futures

Arrowhead Pharmaceuticals to Host R&D Day on Emerging Pipeline of RNAi Therapeutics September 25th, 2018

Arrowhead Pharmaceuticals to Host R&D Day on Emerging Pipeline of RNAi Therapeutics September 25th, 2018

Arrowhead Pharmaceuticals Reports Inducement Grants under NASDAQ Marketplace Rule 5635(c)(4) September 25th, 2018

Viral RNA sensing: Optical detection of picomolar concentrations of RNA using switches in plasmonic chirality September 21st, 2018

Academic/Education

The Institute of Applied Physics at the University of Tsukuba near Tokyo in Japan uses Deben's ARM2 detector to better understand catalytic reaction mechanisms June 27th, 2018

Powering the 21st Century with Integrated Photonics: UCSB-Led Team Selected for Demonstration of a Novel Waveguide Platform Which is Transparent Throughout the MWIR and LWIR Spectral Bands June 19th, 2018

SUNY Poly Professor Eric Lifshin Selected for ‘Fellow of the Microanalysis Society’ Position for Significant Contributions to Microanalysis June 13th, 2018

Grand Opening of UC Irvine Materials Research Institute (IMRI) to Spotlight JEOL Center for Nanoscale Solutions: Renowned Materials Scientists to Present at the 1st International Symposium on Advanced Microscopy and Spectroscopy (ISAMS) April 18th, 2018

Nanotubes/Buckyballs/Fullerenes/Nanorods

Carbon nanodots do an ultrafine job with in vitro lung tissue: New experiments highlight the role of charge and size when it comes to carbon nanodots that mimic the effect of nanoscale pollution particles on the human lung. September 12th, 2018

Graphene nanotubes outperform ammonium salts and carbon black in PU applications September 11th, 2018

S, N co-doped carbon nanotube-encapsulated CoS2@Co: Efficient and stable catalysts for water splitting September 10th, 2018

Peering into private life of atomic clusters -- using the world's tiniest test tubes September 6th, 2018

Discoveries

Searching for errors in the quantum world September 21st, 2018

Viral RNA sensing: Optical detection of picomolar concentrations of RNA using switches in plasmonic chirality September 21st, 2018

UT engineers develop first method for controlling nanomotors: Breakthrough for nanotechnology as UT engineers develop first method for switching the mechanical motion of nanomotors September 21st, 2018

Silver nanoparticles are toxic for aquatic organisms: A research team at the UPV/EHU-University of the Basque Country has analysed how zebrafish are affected in the long term by exposure to silver particles September 19th, 2018

Announcements

Arrowhead Pharmaceuticals to Host R&D Day on Emerging Pipeline of RNAi Therapeutics September 25th, 2018

Arrowhead Pharmaceuticals to Host R&D Day on Emerging Pipeline of RNAi Therapeutics September 25th, 2018

Arrowhead Pharmaceuticals Reports Inducement Grants under NASDAQ Marketplace Rule 5635(c)(4) September 25th, 2018

Viral RNA sensing: Optical detection of picomolar concentrations of RNA using switches in plasmonic chirality September 21st, 2018

Quantum nanoscience

September 5th, 2018

A Novel Graphene Quantum Dot Structure Takes the Cake August 24th, 2018

How hot is Schrödinger's coffee? 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

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