Jan 15, 2009
Graphene modified with electron beams
Irradiating graphene with low-energy electron beams, even for a short time, transforms its crystal lattice into a nano-crystalline form and then into an amorphous material as irradiation dose increases. Researchers at the University of California Riverside say their finding will have implications for making graphene devices, which are often visualised using electron microscopy techniques. The result also points to a new way of processing graphene materials.
"Wonder material" graphene consists of a planar single sheet of carbon arranged in a honeycombed lattice. Graphene has attracted the attention of scientists and engineers since it was discovered a few years ago thanks to its unique electronic and mechanical properties, which make it useful for a host of device applications from transistors to single-molecule detectors. Among the most interesting properties of graphene are its exceptionally high room-temperature electron mobility and extremely high thermal conductivity.
The outstanding current and heat conduction properties of graphene come from its strictly 2D crystalline lattice characterised by a long-range ordering of carbon atoms and the strength of the bonds between these atoms, explained Alexander Balandin. His team, which includes research assistant Desalegne Teweldebrhan, has now discovered that irradiating graphene with a low-energy electron beam transforms the graphene crystal lattice into a nano-crystalline form and then eventually into an amorphous material. "This transformation is accompanied by a drastic change in the properties: graphene goes from being a good conductor of electricity and heat to being an insulator," he told nanotechweb.org.
The finding will be important for making graphene devices, which are often imaged using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and focused ion beam (FIB) processing. "Our result indicates that just visualising graphene using electron beams may lead to a change in the material's properties. This has to be taken into account by those who are trying to make devices from it."
The result also opens up a new way to process graphene because some areas of the material might be converted into insulators using controlled electron beam irradiation, he says.
The scientists are now determining the exact electron beam doses and energies needed to transform graphene into its nanocrystalline form so that the size of the nanocrystals produced can be controlled. "We are planning to use this knowledge to build better graphene transistors and advanced graphene interconnects and heat spreaders," revealed Balandin.
The researchers are working on projects sponsored by the Semiconductor Research Corporation and DARPA through the Focus Center Research Program and its Functional Engineered Nano Architectonic Center and Interconnect Focus Center.
The work was reported in Applied Physics Letters.
About the author
Belle Dumé is contributing editor at nanotechweb.org