Graphene growth on SiC and other substrates using carbon sources
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Graphene growth on SiC and other substrates using carbon sources W. C. Mitchel,1 J. H. Park,1 Howard E. Smith,1 L. Grazulis,1 S. Mou, D. Tomich1, K. Eyink1 and Said Elhamri2 1 Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, Dayton, OH 45433-7707, USA 2Department of Physics, University of Dayton, Dayton, OH 45469, USA
ABSTRACT Direct deposition of graphene from carbon sources on foreign substrates without the use of metal catalysts is shown to be an effective process with several advantages over other growth techniques. Carbon source molecular beam epitaxy (CMBE) in particular provides an additional control parameter in carbon flux and enables growth on substrates other than SiC, including oxidized Si and sapphire. CMBE using thermally evaporated C60 and a heated graphite filament on SiC is reported here. The graphene films were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and Hall effect. Graphene films on Si-face SiC grown using the C60 source have Bernal-like stacking and n-type conduction while those grown using the graphite filament have turbostratic stacking and p-type conduction. The sheet concentration for both n- and p-type doping is linearly dependent on film thickness. INTRODUCTION Since the isolation of single layer graphene was reported by Novoselov et al. in 2004 [1] a variety of techniques have been used to grow or fabricated this material. Novoselov et al. used mechanical exfoliation from natural or artificial graphite. The technique for removing a few layers from the top of a graphite sample with tape was well known in the scanning tunneling microscopy community for some time but the graphene was always discarded with the tape. Mechanical exfoliation still produces the highest electrical quality graphene but the largest areas exfoliated to date are about 100 Pm x 100 Pm and no one has yet developed a reliable process for precisely depositing graphene at specific locations on the substrate by this approach. Perhaps the oldest approach for producing graphene is chemical vapor deposition on metal films. Karu and Beer [2] reported growth of “crystalline films of graphite by pyrolysis of methane on hot single crystal nickel” in 1966. However, this technique did not become a viable means of producing electronic grade graphene until the work of Kim et al. [3] and Li et al. [4]. Growth on both Ni [3] and Cu [4] foils has produced high quality graphene. However, the technique requires somewhat elaborate processes to transfer the graphene from the conductive metal foils to more useful substrates such as oxidized Si and damage can result. Chemical exfoliation of graphene oxide from graphite and subsequent deposition and reduction back to graphene has been reported [5]. This technique is inexpensive and useful for applications that do not require high mobility, such as transparent conductors and interconnects. It was long known in the SiC community that annealing SiC at high temperatures resulted in the sublimation of Si and the fo
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