We present a novel method for the direct metal-free growth of graphene on sapphire that yields high quality films comparable to that of graphene grown on SiC by sublimation. Graphene is synthesized on sapphire via the simple decomposition of methane at 1425-1600 °C. Film quality was found to be a strong function of growth temperature. The thickness, structure, interface characteristics, and electrical transport properties were characterized in order to understand the utility of this material for electronic devices. Graphene synthesized on sapphire is found to be strain relieved, with no evidence of an interfacial buffer layer. There is a strong correlation between the graphene structural quality and carrier mobility. Room temperature Hall effect mobility values were as high as 3000 cm(2)/(V s), while measurements at 2 K reached values of 10,500 cm(2)/(V s). These films also display evidence of the quantum Hall effect. Field effect transistors fabricated from this material had a typical current density of 200 mA/mm and transconductance of 40 mS/mm indicating that material performance may be comparable to graphene on SiC.
We report results from two-dimensional Raman spectroscopy studies of large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large variation in Raman peak position across the sample resulting from inhomogeneity in the strain of the graphene film, which we show to be correlated with physical topography by coupling Raman spectroscopy with atomic force microscopy.We report that essentially strain free graphene is possible even for epitaxial graphene.Graphene exhibits extraordinary electronic properties including an unusually high mobility of the charge carriers. 1 While significant progress toward understanding the properties of graphene has resulted from studying graphene flakes mechanically exfoliated from bulk graphite, 2 these small flakes (< 100 µm 2 ) are most suited for studying the fundamental science of graphene, and are not practical for the development of graphene-based technologies. Alternatively, the sublimation of silicon (Si) from silicon carbide (SiC) to form epitaxial graphene is a promising route for the production of wafer size graphene films. 3 -45678 9 However, rapid characterization and precise control of properties of epitaxial graphene over a wafer-size area are yet to be achieved. Micro-Raman spectroscopy is a rapid, highresolution optical characterization technique that yields important information on the thickness, the charge carrier density, and the strain of epitaxial graphene. 10,11,12,13 However, no studies of Raman topography, the two-dimensional mapping of Raman spectrum over large-area epitaxial graphene, have been carried out to date.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.