http://mota.stanford.edu/molecular_graphene.php

Massless Dirac Fermions Make Graphene As Fast As Lightening

A report, published in Nature, suggests graphene could be the most  sought after material for designer electron devices. Electrons become massless Dirac fermions in graphene as a result of its electronic structure; they travel at the speed of light and are the result of Dirac points that form within the honeycomb lattice of carbon atoms. Graphene is one member of a class of Dirac materials that includes iron-based high-temperature semiconductors, and is show in research conducted by Gomes et al to be a fully tunable condensed-matter system.

Hari C. Manoharan, the corresponding author of the paper, announced in Nature that the team were happy to report,

…the emergence of Dirac fermions in a fully tunable condensed-matter system—molecular graphene—assembled by atomic manipulation of carbon monoxide molecules over a conventional two-dimensional electron system at a copper surface…Molecular graphene provides a versatile means of synthesizing exotic topological electronic phases in condensed matter using tailored nanostructures.

The Stanford graphene research team were able to produce electron field effects that were equivalent to placing an electron in a 60 Tesla magnetic field – a force 30% stronger than any previously produced on Earth. The resulting effect means that the electrons can be tuned to behave in certain ways at the speed of light.

The team used a scanning tunneling microscope to place individual carbon monoxide molecules onto a smooth copper surface. The carbon monoxide naturally repels the electrons on the copper surface and arranges them into a graphene-like honeycomb pattern. Changing the configuration produced effects such as electrons acting as if they had been exposed to a magnetic or electric field; and by introducing defects or impurities the team were also able to mimic changes in carbon-carbon bond lengths and thereby restore the electrons’ mass in small, selected areas.http://mota.stanford.edu/molecular_graphene.php

The final stage of the research was to reposition the carbon monoxide molecules to create an effect similar to that of an incredibly strong magnetic field and thereby to effect a change in symmetry of electron flow.

This graphic shows the effect that a specific pattern of carbon monoxide molecules (black/red) has on free-flowing electrons (orange/yellow) atop a copper surface. Ordinarily the electrons behave as simple plane waves (background). But the electrons are repelled by the carbon monoxide molecules, placed here in a hexagonal pattern. This forces the electrons into a honeycomb shape (foreground) mimicking the electronic structure of graphene, a pure form of carbon that has been widely heralded for its potential in future electronics. The molecules are precisely positioned with the tip of a scanning tunneling microscope (dark blue).

Image credit: Hari Manoharan / Stanford University.

 

For a short video demonstration of the effect visit: http://www.stanford.edu/group/mota/press/molecular_graphene/Assembly.mov

 

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