Robust methods to tune the unique electronic properties of graphene by chemical modification are in great demand due to the potential of the two dimensional material to impact a range of device applications. Here we show that carbon and nitrogen core-level resonant X-ray spectroscopy is a sensitive probe of chemical bonding and electronic structure of chemical dopants introduced in single-sheet graphene films. In conjunction with density functional theory based calculations, we are able to obtain a detailed picture of bond types and electronic structure in graphene doped with nitrogen at the sub-percent level. We show that different N-bond types, including graphitic, pyridinic, and nitrilic, can exist in a single, dilutely N-doped graphene sheet. We show that these various bond types have profoundly different effects on the carrier concentration, indicating that control over the dopant bond type is a crucial requirement in advancing graphene electronics.

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Imaging ellipsometry studies of graphene on SiO 2 / Si and crystalline GaAs are presented. We demonstrate that imaging ellipsometry is a powerful tool to detect and characterize graphene on any flat substrate. Variable angle spectroscopic ellipsometry is used to explore the dispersion of the optical constants of graphene in the visible range with high lateral resolution. In this way, the influence of the substrate on graphene's optical properties can be investigated.

The growth of single layer graphene nanometer size domains by solid carbon source molecular beam epitaxy on hexagonal boron nitride (h-BN) flakes is demonstrated. Formation of single-layer graphene is clearly apparent in Raman spectra which display sharp optical phonon bands. Atomic-force microscope images and Raman maps reveal that the graphene grown depends on the surface morphology of the h-BN substrates. The growth is governed by the high mobility of the carbon atoms on the h-BN surface, in a manner that is consistent with van der Waals epitaxy. The successful growth of graphene layers depends on the substrate temperature, but is independent of the incident flux of carbon atoms. Studies of atomic layers of graphene attract enormous interest for their impact in fundamental science and for their potential to revolutionize applications in diverse areas such as electronics and optoelectronics [1,2]. Much of the exciting research has been reported on high quality graphene obtained by micromechanical exfoliation of graphite. Advances in fundamental and applied research and technology would be greatly enhanced by implementation of scalable fabrication methods. While chemical vapor deposition (CVD) creates the potential for production of large area graphene layers [3,4], device performance of CVD grown films remains low with mobilities as much as 10 times smaller than that measured in exfoliated devices. A promising alternative is the growth of graphene by molecular beam epitaxy (MBE). MBE growth of graphene on substrates patterned at the nanoscale, to give an example, could lead to fabrication of nanostructures with controlled doping and energy gaps [5,6,7,8]. The remarkable potential of MBE grown graphene has resulted in numerous challenging developments [9,10,11,12,13].Single crystal hexagonal boron nitride (h-BN) has been proposed as an ideal substrate for epitaxial growth of graphene by MBE [14,15]. The hexagonal lattice structure yields an atomically flat surface with lattice constant close to that of graphene (less than 2% mismatch). h-BN is also an inert large-band-gap insulator that can withstand very high temperatures. Further, it has been recently demonstrated that h-BN is an ideal substrate for electrical transport devices fabricated from exfoliated graphene flakes [16,17,18].In this letter we report the MBE growth of single layer graphene on single crystal h-BN flakes. Characterization of the MBE grown graphene layers by Raman-scattering spectroscopy and atomic-force microscope (AFM) imaging indicate that the graphene layers consist of nanoscale domains. The non-uniformity of the growth suggests that the individual characteristics of the h-BN flakes, such as surface morphology, may play a significant role. The maximum substrate temperature that can be reached before the SiO 2 substrate decomposes is a key parameter limiting the growth conditions in this work. The quality of the layers depends critically on the substrate temperature during growth. The best results are obtained at growth temperat...

We demonstrate the growth of graphene nanocrystals by molecular beam methods that employ a solid carbon source, and that can be used on a diverse class of large area dielectric substrates. Characterization by Raman and Near Edge X-ray Absorption Fine Structure spectroscopies reveal a sp