Counting graphene layers: researchers from NTT and University of Tokushima
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.