2 graphene layers may be better than 1

This is more progress coming outof the world of graphene research which has been breathtaking.  Most important is that we have been quicklybecoming better skilled at producing and manipulating the material and modifyingits behavior.

Its importance is extraordinary andwe can see the day in which it is the principle building block of all technology.

In this case we discover we cancreate puddles of opposite charge between the two layers.  Sounds like an electrical device to me.

I wonder what all the radioenthusiasts of the first half of the twentieth century would have thought ofall this.

2 graphene layers may be better than 1

by Staff Writers

Washington DC (SPX) Apr 29, 2011NIST

measurements show that interactions of the graphene layers with theinsulating substrate material causes electrons (red, down arrow) and electronholes (blue, up arrow) to collect in "puddles." The differing chargedensities creates the random pattern of alternating dipoles and electon bandgaps that vary across the layers. Credit: NIST

http://www.spacedaily.com/reports/2_graphene_layers_may_be_better_than_1_999.html

Researchers at the National Institute of Standards andTechnology (NIST) have shown that the electronic properties of two layers ofgraphene vary on the nanometer scale.

The surprising new results reveal that not only does the difference inthe strength of the electric charges between the two layers vary across thelayers, but they also actually reverse in sign to create randomlydistributed puddles of alternating positive and negative charges.

Reported in Nature Physics,*the new measurements bring graphene a step closer to being used in practicalelectronic devices.

Graphene, a single layer of carbon atoms, is prized for its remarkableproperties, not the least of which is the way it conducts electrons at highspeed.

However, the lack of what physicists calla band gap-an energetic threshold that makes it possible to turn a transistoron and off-makes graphene ill-suited for digital electronic applications.

Researchers have known that bilayer graphene, consisting of two stackedgraphene layers, acts more like a semiconductor when immersed in an electric field.

According to NIST researcher Nikolai Zhitenev, the band gap may alsoform on its own due to variations in the sheets' electrical potential caused byinteractions among the graphene electrons or with the substrate (usually anonconducting, or insulating material) that the graphene is placed upon.

NIST fellow Joseph Stroscio says that their measurements indicate thatinteractions with the disordered insulating substrate material causes pools ofelectrons and electron holes (basically, the absence of electrons) to form inthe graphene layers.

Both electron and hole "pools" are deeper on the bottom layerbecause it is closer to the substrate. This difference in "pool"depths, or charge density, between the layers creates the random pattern ofalternating charges and the spatially varying band gap.

Manipulating the purity of the substrate could give researchers a wayto finely control graphene's band gap and may eventually lead to thefabrication of graphene-based transistors that can be turned on and off like asemiconductor.

Still, as shown in the group's previous work**, while these substrateinteractions open the door to graphene's use as a practical electronicmaterial, they lower the window on speed.

Electrons do not move as well through substrate-mounted bilayergraphene; however, this may likely be compensated for by engineering thegraphene/substrate interactions.

Stroscio's team plans to explore further the role that substrates mayplay in the creation and control of band gaps in graphene by using differentsubstrate materials.

If the substrate interactions can be reduced far enough, says Stroscio,the exotic quantum properties of bilayer graphene may be harnessed to create anew quantum field effect transistor.