Graphene growth on SiC and metal surfaces by solid carbon source deposition
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Graphene growth on SiC and metal surfaces by solid carbon source deposition W. C. Mitchel,1 J. H. Park,1 H. E. Smith,1 L. Grazulis,1 and K. Eyink1 1 Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, Dayton, OH 45433-7707 ABSTRACT Graphene has been grown by direct deposition of carbon from solid sources on both SiC and Ta films on SiC in an MBE environment. Carbon fluxes were obtained from thermally evaporated C60 and from a heated graphite filament. The graphene films were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Graphene films on Si-face SiC grown by carbon source MBE (CSMBE) were compared with graphene grown by the standard epitaxial graphene process using SiC thermal decomposition. CSMBE on SiC was found to grow at lower temperatures (1200ºC) and to have fewer pits and a more uniform surface. Uniform graphene films were found to grow on Ta films after exposure to both carbon sources at 1200ºC but Raman measurements showed no signs of graphene on films exposed to the same temperature without a carbon flux.
INTRODUCTION Graphene was isolated by Novoselov et al. in 2004 [1] using mechanical exfoliaton from graphite. Since then interest in this material has exploded due to its unique and exciting properties. While exfoliated graphene is relatively easy to prepare and results in some of the best material, it is limited to individual flakes less than a square millimeter in size. Two processes are now under development to make large area electronic grade graphene. Relatively high quality films of graphene have been grown by the thermal decomposition of SiC [2, 3]. In this process the SiC is heated to a temperature above 1300ºC in either vacuum [3] or atmospheric pressure argon [4], after which Si sublimes, leaving carbon which forms into graphene. This approach is referred to in the literature as epitaxial graphene because of the close lattice match between graphene and the carbon rich surface reconstruction of the Si face of SiC. Graphene can also be grown directly from gaseous carbon sources by heating metal films in the presence of hydrocarbon sources which decompose [5]. The free carbon is dissolved into the metal and subsequently precipitates out as graphene when the film is cooled. Li et al. [6] have also demonstrated growth on copper films in which it is believed the carbon forms directly into graphene without dissolving into the copper. Growth on metal films is usually referred to as CVD graphene. All of these approaches have limitations. The epitaxial graphene process lacks control since the only parameters that can be varied are the substrate temperature and the chamber pressure. CVD graphene is believed to have contaminants from the metal films. Further, the graphene has to be removed from the metal for practical applications. Recently several groups have investigated MBE-like growth of using graphite based carbon sources. Hackley et al. [7] reported growth of graphitic films directly on Si(111). AlTemimy et a
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