AVS 54th International Symposium
    Thin Film Tuesday Sessions
       Session TF-TuM

Paper TF-TuM6
Production of Large Area Graphene Sheets by Si Desorption from SiC

Tuesday, October 16, 2007, 9:40 am, Room 613/614

Session: Two-Dimensional Carbon Nanostructures
Presenter: G.G. Jernigan, U.S. Naval Research Laboratory
Authors: G.G. Jernigan, U.S. Naval Research Laboratory
J.C. Culbertson, U.S. Naval Research Laboratory
B.L. VanMil, U.S. Naval Research Laboratory
K.K. Lew, U.S. Naval Research Laboratory
R.L. Myers-Ward, U.S. Naval Research Laboratory
D.K. Gaskill, U.S. Naval Research Laboratory
P.M. Campbell, U.S. Naval Research Laboratory
E.S. Snow, U.S. Naval Research Laboratory
Correspondent: Click to Email

With DeHeer’s1 initial report of graphene formation by the thermal desorption of Si from SiC, efforts have been underway to use this method to make large area sheets of graphene for device fabrication purposes. Mobility measurements of graphene on SiC, however, have not approached the values obtained with graphene exfoliated from graphite, indicating that material issues and other factors may be affecting the quality of graphene from SiC. We will report on our efforts to produce large area graphene sheets using 2- and 3-, Si-face, 4H and 6H SiC wafers. Using x-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), atomic force microscopy (AFM), Raman spectroscopy, and electrical characterization, we have studied graphene sheets and graphite films formed on SiC by Si desorption in ultra-high vacuum (UHV). The wafers were initially subjected to hydrogen etches at 1400 °C and 1580 °C to remove polishing damage and to produce smooth surfaces prior to entrance into UHV. XPS measurements show the hydrogen-etched surfaces are initially covered by an oxide, which can be desorbed at 1000 °C in UHV resulting in a surface containing excess Si. At ~1300 °C, the surface becomes stoichiometric in Si and C and a √3 x √3 R30 LEED pattern is observed. At ~1350 °C, we observe a 6√3 x 6√3 R30 LEED pattern develop when graphene has formed, and a 1x1 LEED pattern for graphite films formed at temperatures greater than 1400 °C. AFM images show that the process of Si desorption from the surface results in the formation of hexagonal pits and that the liberation of carbon onto the surface produces the graphene layer. As more Si is desorbed from the surface, the carbon forms into 3-dimensional islands with a hexagonal shape. Interestingly, the sheet conductance remains constant while the islands coalesce into a thick graphite layer. Raman spectroscopy of the graphene sheets is complicated by strong transitions from the underlying SiC substrate. Nonetheless, D, G, and D’ lines can be distinguished, and their intensities are observed to increase with increasing sheet thickness. The frequency of the D’ line can also be used to distinguish the formation of graphene and graphitic material. We will discuss how process parameters affect the graphene quality as judged by the multiple techniques.

1J. Phys. Chem. B 108, 19912-19916 (2004).