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article imageGraphene yields the world’s smallest crack

By Tim Sandle     Apr 29, 2015 in Science
A new method, designed to create more powerful and faster nanoscale devices, has led to fabricated nanostructures with atomic sized gaps. These "cracks" are reportedly the smallest ever.
By using graphene (a single layer of carbon atoms) researchers have created gaps no more than one atom thick (which the researchers term “nanogaps.”) The means to produce a smaller nanogap between two given nanostructures is to use a graphene spacer. This needs to be carefully etched away in order to create the gap. These spacers are 100,000 times thinner than a human hair (approximately 0.3 nanometers in length.) With the gaps, a nanosized contact is formed by electromigration. This acts like a waveguide for electrons. Electromigrated Nanogaps have shown promise as electrodes in use in molecular scale electronics.
The basis for creating the nanogaps starts with the production of thin films where a single layer of graphene is locked between two gold metal sheets. To begin with, graphene is grown on a copper substrate, and then layered on top with a sheet of gold metal. As graphene fixes more tightly to gold than to copper, the entire graphene single-layer can readily be removed and it remains intact. Thus a single-layer graphene is placed between two metals.
When the gold/graphene composite is separated from the copper substrate, the exposed side of the graphene layer is then connected with another gold sheet to produce the gold:single-layer graphene:gold thin film.
Following this, the films are sliced into 150 nm-wide nanostructures. As the final step, the structures are treated with oxygen plasma to remove graphene. The result is the smallest ever nanogaps between the gold layers.
Graphene is formed of pure carbon and it is one of the thinnest, lightest and strongest materials known to humankind.
The objective is to use this physical property to detect single molecules associated with certain diseases. This is based on different molecules having different properties within an electromagnetic field. The different signals can potentially act as disease markers.
A longer-term research goal is to develop computer microprocessors that are 100 times smaller than those used today. Here, reducing the spacing between electronic circuits on a microchip allows a greater number of circuits to be installed onto the same chip. In turn this raises the computing power of a device.
The technique has yet to be fully perfected; the researchers report that some residue to graphene remains and this leads to unreliability with electronic devices.
The study was carried out at the University of California, San Diego. The findings have been published in the journal Nano Letters. The research paper is titled “Using the Thickness of Graphene to Template Lateral Subnanometer Gaps between Gold Nanostructures.”
In related news, scientists at Melbourne’s Swinburne University of Technology have used to graphene as the basis of a new generation of 3D computer and holographic images. Key to this is a single femtosecond (fs) laser pulse can reduce graphene oxide to “photo-reduced graphene oxide.” Further details are presented in the journal Nature Communications (“Athermally photoreduced graphene oxides for three-dimensional holographic images.”)
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