The recent demonstration of the ability to “fully engineer the electronic band gap of graphene” is a major advance in the top-down approach to nanotech applications that take advantage of the many marvelous properties of graphene. From “STM cuts graphene to size,” nanotechweb.org, written by Belle Dumé (requires free registration):
Researchers in Hungary and Belgium have developed the most precise nanolithography technique ever. Levente Tapasztó of the Research Institute for Technical Physics and Materials Science in Budapest and colleagues have already used the method, which employs the tip of a scanning tunnelling microscope, to pattern tiny nanostructures (ribbons) into a graphene sheet. The technique makes it possible to build entire working circuits and avoids the disadvantages of “bottom up” methods that rely on assembling individual building blocks, such as carbon nanotubes.
We have realized truly nanometre precision lithography,” Tapasztó told nanotechweb.org. “This allows us to fabricate nanostructures with the desired atomic structure and therefore good electronic properties.”
The technique allows materials to be “cut” to the required shape and dimensions at the nanoscale. This is a huge step forward, says Tapasztó, because until now researchers had to rely on finding suitable blocks, like carbon nanotubes with the correct structure, to fabricate nanoscale electronic devices.
The team, which includes researchers from Facultés universitaire Notre Dame de la Paix in Namur, Belgium, made nanostructures by bombarding a graphene sheet with electrons emitted from an atomically sharp tip positioned just a few angstroms above the surface of the material. This “local access” ensures that the technique is precise. By moving the tip along a given geometry, different shapes can be patterned. A big advantage of the technique is that it allows in-situ atomic-scale resolution imaging of the sample immediately after it has been shaped.
By controlling both the width and crystallographic orientation of the nanoribbons, the method is the first to be able to fully engineer the electronic band gap of graphene. “Moreover, the accuracy of STM lithography also allows for downscaling, which is important since it enables us to open energy gaps large enough for room-temperature operation of graphene-based electronic devices,” explained Tapasztó. Indeed, the team has managed to reduce a nanoribbon to just 2.5 nm wide (about 20 carbon atoms). This is far beyond the capabilities of current state-of-the-art electron beam lithography, which can only go down to around 20 nm.
The research was published in Nature Nanotechnology (abstract).
—Jim
