Characteristics of graphite films on silicon- and carbon -terminated faces of silicon carbide.

摘要

Ultrathin graphite films grown on silicon carbide (SiC) form a promising platform for ballistic-carrier devices based on nano-patterned epitaxial graphene [11]. Graphite films with thickness from 1--30 atomic layers are grown on the Si-terminated (0001) face and C-terminated (0001¯) face of 6H-SiC and 4H-SiC via thermal desorption of silicon in an ultrahigh vacuum (UHV) chamber or in a high-vacuum RF furnace. The growth of graphite films is investigated with low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and scanning tunneling microscopy (STM). Graphite LEED patterns and atom-resolved STM images on graphite films prove that epitaxial growth is achieved on both faces of the SiC substrate. The thickness of graphite films is estimated with two methods, modeling the Si:C Auger peak to peak intensities with simplified assumptions and curve-fitting of synchrotron X-ray diffraction peaks.;Through LEED and STM investigations of monolayer graphite grown on the Si-face of 6H-SiC(0001), we show the existence of a SiC 63x63 R30° reconstructed layer between graphite films and the SiC substrate. The graphite films prepared on the Si-face have less than 0.2A vertical amplitude corrugation following a SiC 6x6 periodicity. We prove that this assumption is related to the SiC 63x63 R30° reconstruction layer. We also prove that the kinematic scattering from the SiC 63x63 R30° interfacial structure gives a good interpretation of the complicated 63x63 R30° LEED diffraction patterns, which traditionally are regarded as the result of double-scattering from the graphite film and SiC substrate. The graphitized surfaces show structurally coherent 50nm2 domains with surface height difference between adjacent domains in the same terrace varying from 0.5A to 3.0A. The minimum corresponds to the Si-C vertical separation within one SiC bilayer and the maximum to the graphite interlayer spacing. Further scanning tunneling spectroscopy (STS) measurements and low temperature STM show that the graphite films remain continuous over the steps between domains.;Ultrathin graphite films grown on the C-face of 6H-SiC(0001¯) in the UHV chamber or in the RF furnace are also investigated. Some areas of the surface prepared in RF furnace are covered by nanocaps or nanotubes, and the remaining areas are flat graphite films. The huge nanotube-like bumps often form common boundaries of the domains. The graphitized C-face surface generally has larger size domains and terraces than Si-face according to AFM and X-ray experiments. LEED patterns from the thinnest C-face films show epitaxial growth on the SiC substrate, however split diffraction arcs in the LEED pattern from thicker films indicate azimuthal disorder.