Jun 4, 2009
Helium ions etch graphene devices
A new non-contact method to etch graphene has been invented by researchers at Harvard University and MIT. The technique, which involves using a helium ion beam to produce features smaller than 10 nm, is a direct etch method that does not require resists or chemical/plasma etching.
Graphene consists of a planar single sheet of carbon arranged in a honeycombed lattice. The material has attracted the attention of scientists and engineers since it was discovered in 2004 thanks to its unique electronic and mechanical properties, which make it useful for a host of device applications from transistors to single-molecule detectors.
Most experiments have concentrated on making graphene devices from graphene nanoribbons or quantum dots. Such structures are typically between 5 and 50 nm in size and are made using electron beam lithography followed by reactive ion etching, or by chemical techniques such as unfolding carbon nanotubes. Although these methods are good for producing devices with near-atomic dimensions, they can damage the material. For example, resist masks can produce graphene with disordered edges and chemical methods often result in irregular-shaped flakes unsuitable for integrated device applications.
Now, Max Lemme and David Bell of Harvard together with colleagues at MIT have come up with a possible alternative. The researchers use a helium ion microscope (Zeiss ORION) as a lithography tool to etch nanostructures in graphene. The beam is sub-nanometre in size and benefits from the short de Broglie wavelength of helium, which is around 100 times smaller than the corresponding electron wavelength. This means the beam has a resolution of just 0.5 nm or better, making it excellent for such precision lithography.
"The fact that the technique is non-contact is critical for materials like graphene that are one atom thick," team leader Charles Marcus told nanotechweb.org. "Anything that touches the surface – such as electron beam resists or photoresists – can chemically dope the material, creating noise and disorder."
The new technique is currently the only way to directly modify single atomic layers of graphene without significantly damaging the surrounding regions, add Lemme and Bell. It can be used to produce structures smaller than 10 nm.
According to the Harvard–MIT team, the method could be used to make devices for high-speed electronics and to provide a platform for new physics experiments in the field of quantum information.
"The technique has the potential to revolutionize the way that very thin, one-atomic layer materials are modified in a controlled and predictable way," said Lemme and Bell. "This may open a way for graphene technology to enter the semiconductor industry."
The work was reported on arXiv.
About the author
Belle Dumé is contributing editor at nanotechweb.org