Graphene lenses for electrons

April 23, 2012

Graphen lens (credit: Karlsruhe Institute of Technology)

Graphene, the one-atom-thick “wonder material” made of carbon, has another potential use in the world of high-speed electronics — as a tool that can focus a stream of electrons similar to the way an optical lens focuses light.

A new prototype reveals that a layer of graphene, when strained by stretching, can act as a two-dimensional lens for electrons. The research was produced by an international group of researchers from the Karlsruhe Institute of Technology in Germany and the French National Center for Scientific Research (CRNS).

Graphene is an excellent conductor: electrons flow freely across its surface in straight lines. According to a previously proposed theory, highly strained graphene impedes the flow of electrons, slowing them down and altering their trajectory. Scientists believed this effect could be used to focus electrons to a fine point — similar to the way an optical lens creates areas of refraction, or bending, to shepherd light to a point.

To create the prototype lens, the team of French and German researchers built a “deformed graphene carpet” that smoothly covers a series of hexagonal nano-holes in a silicon-carbide wafer. Areas of the graphene were strained as they adopted the shape of the holes in the wafer. The researchers found that they could control the focal length of a graphene lens by changing its geometry.

Practical applications of this work include uses in high-speed electronics, where strained graphene could act as a transport medium for information exchange between different parts of a circuit. Unlike traditional information exchange, in which electrons flow through cables whose paths cannot cross without a short, the new method would allow electrons an unprecedented freedom of movement, similar to that of light in a vacuum.

“The advantage of this method can be seen if you have n contacts, between those you would like to send information. With cables, you need for every connection one cable (that make n(n-1)/2 cables). In the new way, you can use lenses to focus electrons from one contact to another contact. Thus, you only need one two-dimensional graphene layer for the information transport and all the n(n-1)/2 paths of the electrons can just cross each other in the layer,” adds Karlsruhe Institute of Technology’s Dr. W. Wulfhekel.

Ref.: L. Gerhard, et al., A graphene electron lens, Applied Physics Letters, 2012; [DOI:10.1063/1.3701594]