Graphene single crystals with dimensions of up to 0.5 mm on a side were grown by low-pressure chemical vapor deposition in copper-foil enclosures using methane as a precursor. Low-energy electron microscopy analysis showed that the large graphene domains had a single crystallographic orientation, with an occasional domain having two orientations. Raman spectroscopy revealed the graphene single crystals to be uniform monolayers with a low D-band intensity. The electron mobility of graphene films extracted from field-effect transistor measurements was found to be higher than 4000 cm(2) V(-1) s(-1) at room temperature.

The fundamental properties of graphene are making it an attractive material for a wide variety of applications. Various techniques have been developed to produce graphene and recently we discovered the synthesis of large area graphene by chemical vapor deposition (CVD) of methane on Cu foils. We also showed that graphene growth on Cu is a surface-mediated process and the films were polycrystalline with domains having an area of tens of square micrometers. In this paper, we report on the effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy. On the basis of the results, we developed a two-step CVD process to synthesize graphene films with domains having an area of hundreds of square micrometers. Scanning electron microscopy and Raman spectroscopy clearly show an increase in domain size by changing the growth parameters. Transmission electron microscopy further shows that the domains are crystallographically rotated with respect to each other with a range of angles from about 13 to nearly 30°. Electrical transport measurements performed on back-gated FETs show that overall films with larger domains tend to have higher carrier mobility up to about 16,000 cm(2) V(-1) s(-1) at room temperature.

The effects of residues introduced during the transfer of chemical vapor deposited graphene from a Cu substrate to an insulating (SiO 2) substrate on the physical and electrical of the transferred graphene are studied. X-ray photoelectron spectroscopy and atomic force microscopy show that this residue can be substantially reduced by annealing in vacuum. The impact of the removal of poly(methyl methacrylate) residue on the electrical properties of graphene field effect devices is demonstrated, including a nearly 2 Â increase in average mobility from 1400 to 2700 cm 2 /Vs. The electrical results are compared with graphene doping measurements by Raman spectroscopy. V

The contact resistance of metals on backgated graphene field-effect transistors is studied. The residual resistance obtained at high backgate voltage is found to be in excellent agreement with the extracted values of contact resistance from transfer length measurements on graphene flakes. The contact resistance is found to be a significant contributor to the total resistance of graphene-based devices. The specific contact resistance is shown to be independent of the applied backgate voltage and the number of graphene layers.

Field-effect transistors fabricated on graphene grown by chemical vapor deposition (CVD) often exhibit large hysteresis accompanied by low mobility, high positive backgate voltage corresponding to the minimum conductivity point (V(min)), and high intrinsic carrier concentration (n(0)). In this report, we show that the mobility reported to date for CVD graphene devices on SiO(2) is limited by trapped water between the graphene and SiO(2) substrate, impurities introduced during the transfer process and adsorbates acquired from the ambient. We systematically study the origin of the scattering impurities and report on a process which achieves the highest mobility (μ) reported to date on large-area devices for CVD graphene on SiO(2): maximum mobility (μ(max)) of 7800 cm(2)/(V·s) measured at room temperature and 12,700 cm(2)/(V·s) at 77 K. These mobility values are close to those reported for exfoliated graphene on SiO(2) and can be obtained through the careful control of device fabrication steps including minimizing resist residue and non-aqueous transfer combined with annealing. It is also observed that CVD graphene is prone to adsorption of atmospheric species, and annealing at elevated temperature in vacuum helps remove these species.