Probing the electronic properties of graphene on C-face SiC down to single domains by nanoresolved photoelectron spectroscopies

Abstract

Graphene samples with thicknesses ranging from monolayer to few layer graphene grown on the C-face of SiC by Si flux-assisted molecular beam epitaxy were studied to understand their stacking structure. Particular attention was put on determining the size, thickness, spatial distribution, and orientation relative to the SiC of the graphene domains. A complete electronic characterization of the graphene films down to submicrometer grains was obtained by using synchrotron-based conventional and nanoresolved photoelectron spectroscopies. These measurements were completed with scanning probe techniques like atomic force and scanning tunneling microscopies. By probing exactly the same region of the samples using angular-resolved and core-level photoelectron spectroscopy imaging and point modes, we were able to identify two types of grains constituting the graphene films with radically different thickness, stacking and orientation. The size, distribution, and registry with the substrate for each type of grain were determined. Most interestingly, we have evidenced that multilayer graphene grains with Bernal stacking coexist with areas composed of twisted bilayer graphene grains.

NanoARPES of twisted bilayer graphene on SiC: absence of velocity renormalization for small angles

“…The N and W bandwidths are large, which may originate from nearly aligned different grains considering that the beam size is larger than the grain size. The N width is 0.06 Å −1 26 , and the W width is even larger, because its continuous orientation distribution is much wider. To overcome this limitation, we have utilized the state-of-the-art high spatial resolution scanning photoemission k-microscope at the ANTARES beamline.…”

“…Consequently, using the point mode acquisition, we could measure the band structure within any single N or W grain. After correlated nanoARPES and nano core-level experiments 26 , we showed that N grains only involve AB stacked multilayers (typically 4–6 ML, see supplementary information Fig. S1 ) while W grains mainly include TBG.…”

“…Graphene single grains on SiC(000 ) are oriented along two preferred azimuths 26 27 28 29 . The low energy electron diffraction (LEED) pattern in Fig.…”

“…The novelty of this work lies in the direct measurement of the band structure within individual TBG grains with small twist angles, thus leading to an accurate determination of band velocity. These experiments were achieved in exactly 2 monolayer (ML)-thick grains, calibrated by simultaneous core-level and ARPES measurements with nanometric lateral resolution 26 . Because the photon spot size was much smaller than the TBG grains, we were able to measure the band structure close to the Dirac point of single TBG grains for small twist angles: no velocity renormalization occurred at 2.1° and 1.8° ± 0.6° twist angles.…”

Growth of 3C-SiC and Graphene for Solar Water-Splitting Application

“…It has been extensively found that graphene grown on the C-face hexagonal SiC presents smaller domains with a larger distribution of graphene thickness than on the Si-face [39,[53][54][55][56][57]. Unlike the Si-face, there is no evidence to manifest the existence of a buffer layer on graphene/C-face SiC samples so far, although (2  2), (3  3) surface reconstructions were observed [58].…”