Sep 7, 2010
Counting the number of graphene layers grown on SiC
Graphene is a two-dimensional sheet of sp2-bonded carbon atoms in a honeycomb lattice. Graphene sheets comprising from one to a few layers of graphene (few-layer graphene) exhibit many fascinating properties and have various potential applications. In particular, because the miniaturization of silicon transistors is approaching its limit, many people are anticipating a new paradigm of carbon nanoelectronics in which graphene could play a central role due to its superior transport properties and compatibility with the standard lithographic techniques.
Counting graphene layers: researchers from NTT and University of Tokushima
However, a large-scale graphene-production method, which is indispensable to the practical applications, has not yet been established. Thermal decomposition of SiC is a simple, easy way of fabricating graphene on a wafer scale. Graphene always grows epitaxially on a Si-face SiC substrate, and in addition, graphene layers continuously cover the substrate like a carpet, possibly everywhere on the sample. We believe epitaxial graphene on SiC is the most viable route to producing a single-crystal graphene substrate.
By optimizing the growth conditions in ultrahigh vacuum on the basis of in situ LEEM observations, we have succeeded in growing epitaxial bilayer graphene with the largest uniform area to date. The uniform bilayer region is large enough for the transport properties of pure bilayer graphene to be examined using devices fabricated by photolithography.
Recently, we also grew monolayer graphene with a micrometre size by thermal decomposition in Ar atmosphere, a known method of growing a uniform monolayer. This enabled us to compare the transport properties of epitaxial monolayer and bilayer graphene using top-gate Hall devices. Quantum Hall effects were observed in monolayer graphene Hall devices under gate control. Bilayer graphene transistors provided higher on/off ratios than monolayer ones. Relatively uniform monolayer and bilayer graphene sheets were confirmed to span several millimeters. These graphene substrates should have a strong impact on both the basic research and device applications of graphene.
The researchers presented their work in J. Phys D: Appl. Phys.
About the author
Dr Hibino has been studying dynamical processes on semiconductor surfaces using various microscopic techniques such as LEEM. Currently, his main interest is epitaxial graphene growth. Dr Kageshima has been studying physics in semiconductor nanostructures and computational physics technologies. He is investigating theoretically the atomic and electronic structures of graphene using the first-principles method. Dr Nagase has researched fabrication processes for mesoscopic devices. He is investigating electrical properties of epitaxial graphene using the scanning probe techniques. Drs Hibino and Kageshima are senior Research Scientists at NTT Basic Research Laboratories. Dr Nagase has been a professor in the Department of Electrical and Electronic Engineering at the University of Tokushima since 2010. This work was partly supported by KAKENHI (19310085, 21246006) from the Japan Society for the Promotion of Science.