nanotimes News in Brief
10-09 :: September 2010
Graphene // New Fabrication Method Uses Silicon Carbide Template
esearchers at the Georgia Institute of Technology, USA, have developed a new “templated growth”
technique for fabricating nanometer-scale graphene devices.The technique involves etching patterns into the silicon carbide surfaces on which epitaxial graphene is grown. The patterns serve as templates directing the growth of graphene structures, allow- ing the formation of nanoribbons of specific widths without the use of e-beams or other destructive cutting techniques. Graphene nanoribbons produced with these templates have smooth edges that avoid electron-scattering problems.The new technique has been used to fabricate an array of 10,000 top-gated graphene transistors on a 0.24cm2
believed to be the largest density of graphene de- vices reported so far.
In creating their graphene nanostructures, De Heer and his research team first use conventional microe- lectronics techniques to etch tiny “steps” – or con- tours – into a silicon carbide wafer. They then heat the contoured wafer to approximately 1,500° Celsius (2.732° F), which initiates melting that polishes any rough edges left by the etching process. They then use established techniques for growing graphene from silicon carbide by driving off the silicon atoms from the surface. Instead of producing a consistent layer of graphene one atom thick across the surface of the wafer, however, the researchers limit the he- ating time so that graphene grows only on the edges
of the contours. To do this, they take advantage of the fact that graphene grows more rapidly on certain facets of the silicon carbide crystal than on others. The width of the resulting nanoribbons is proportio- nal to the depth of the contour, providing a mecha- nism for precisely controlling the nanoribbons. To form complex graphene structures, multiple etching steps can be carried out to create a complex tem- plate, de Heer explained.
In nanometer-scale graphene ribbons, quantum con- finement makes the material behave as a semicon- ductor suitable for creation of electronic devices. But in ribbons a micron or more wide, the material acts as a conductor. Controlling the depth of the silicon carbide template allows the researchers to create these different structures simultaneously, using the same growth process.
“By using the silicon carbide to provide the template, we can grow graphene in exactly the sizes and sha- pes that we want,” he said. “Cutting steps of vari- ous depths allows us to create graphene structures that are interconnected in the way we want them to be. The same material can be either a conductor or a semiconductor depending on its shape,” noted de Heer, who is also a faculty member in Geor- gia Tech’s National Science Foundation-supported Materials Research Science and Engineering Center (MRSEC). “One of the major advantages of graphene