Graphene-based method enables miniscule gaps in nanostructures

Researchers at the UC San Diego invented a graphene-based way of fabricating nanostructures that contain well-defined, atomic-sized gaps. Such structures could be used to detect single molecules associated with certain diseases and may lay the foundation for miniature microprocessors.

The ability to create these nanogaps is highly desirable in fabricating nanoscale structures, which are typically used as components in optic and electronic devices. By decreasing the spacing between electronic circuits on a microchip, for example, one can fit more circuits on the same chip to produce a device with enhanced computing power. The scientists managed to create nanogaps between two nanostructures, that are much smaller than previously ones by using a graphene spacer, which can be etched away to create the gap.  

The scientists designed a method for making nanogaps, that begins with the production of thin films in which a single layer of graphene is sandwiched between two gold metal sheets. First, graphene is grown on a copper substrate, and then layered on top with a sheet of gold metal. Since graphene clings better to gold than to copper, the entire graphene single-layer can be easily removed and remains intact over large areas. Compared to other techniques that are used to produce similar layered structures, this method allows graphene to be transferred to gold film with minimal defects or contamination. This is referred to as metal-assisted exfoliation.

Once the gold/graphene composite is separated from the copper substrate, the newly exposed side of the graphene layer is sandwiched with another gold sheet to produce the gold-single-layer graphene-gold thin film. The films are later sliced into 150 nm-wide nanostructures. Finally, the structures are treated with oxygen plasma to remove graphene. Scanning electron micrographs of the structures reveal extremely small nanogaps between the gold layers. 

While this technique can produce nanostructures suitable for optical applications, it also exhibits a major disadvantage for electronic applications. Raman spectroscopic measurements of the gold nanostructures reveal that small amounts of graphene still remain between the gold layers after being treated with oxygen plasma. This means that only the graphene exposed near the surfaces of the gold nanostructures can be removed so far. Having graphene still in the structures is not desirable for electronic devices, which require an entire gap between the structures. The team is working to figure out how to solve this problem. Another challenge still ahead is finding ways to vary the thickness of the well-defined gap between the structures. 

Source: ucsdnews