Thermal exfoliation of fluorinated graphite

International audienceThe thermal exfoliation of graphite fluoride was investigated using two starting materials: fluorinated HOPG and powdered room temperature graphite fluoride (RTGF) post-treated in pure F2 gas in order to adjust the relative contents of intercalated species, the carbon hybridization and the C–F bonding. Firstly, the thermal exfoliation of HOPG sample (of composition CF0.57) at the nanoscale is highlighted using scanning tunneling microscopy (STM). Such process involves a defluorination, which is accelerated by disruption of the graphene sheets. Similar breaking occurs during the exfoliation of post-treated RTGF and evolves CF4 and C2F6 gases. Moreover, the exfoliation using a thermal shock is assisted by the fast deintercalation of the catalyst species in the region where the covalence of the C–F bonds is weakened. In such way, exfoliation occurs with the quasi-total defluorination

Highly n-doped graphene generated through intercalated terbium atoms

We obtained highly n-type doped graphene by intercalating terbium atoms between graphene and SiC(0001) through appropriate annealing in ultrahigh vacuum. After terbium intercalation angle-resolved-photoelectron spectroscopy (ARPES) showed a drastic change in the band structure around the K points of the Brillouin zone: the well-known conical dispersion band of a graphene monolayer was superposed by a second conical dispersion band of a graphene monolayer with an electron density reaching 10(15) cm(-2). In addition, we demonstrate that atom intercalation proceeds either below the buffer layer or between the buffer layer and the monolayer graphene. The intercalation of terbium below a pure buffer layer led to the formation of a highly n-doped graphene monolayer decoupled from the SiC substrate, as evidenced by ARPES and x-ray photoelectron spectroscopy measurements. The band structure of this highly n-doped monolayer graphene showed a kink (a deviation from the linear dispersion of the Dirac cone), which has been associated with an electron-phonon coupling constant one order of magnitude larger than those usually obtained for graphene with intercalated alkali metals

Morphology and composition of Au catalysts on Ge(111) obtained by thermal dewetting

International audienceWe investigate the chemical and morphological structure of the Au nanodots on Ge(111) which serve as catalysts for the formation of epitaxial Ge nanowires. The spatial localization of Au is investigated by X-ray spectromicroscopy and transmission electron microscopy. We show that dewetting of an Au film on Ge(111) gives rise to a thin Au-Ge wetting layer and Au-Ge dots. These dots are crystallized but not with a single crystallographic orientation. Thanks to the spatially resolved X-ray and transmission electron microscopy measurements, a chemical characterization of both binary Au-Ge catalysts and wetting layer is obtained at the nanoscale. We show that Ge vertical growth is achieved even without external Ge supply