32 research outputs found
Deuterium adsorption on (and desorption from) SiC(0001)-(3×3), (√3×√3)R30°, (6√3×6√3)R30° and quasi-free standing graphene obtained by hydrogen intercalation
International audienceWe present a comparative high-resolution electron energy-loss spectroscopy study on the interaction of atomic hydrogen and deuterium with various reconstructions of SiC(0 0 0 1). We first show that on both the (3 × 3) and reconstructions, deuterium atoms only bind to silicon atoms, thereby confirming the silicon-rich appellation of these reconstructions. Deuterium passivation of the (3 × 3) is only reversible when exposed to atomic deuterium at a surface temperature of 700 K since tri- and dideuterides, necessary precursors for silicon etching, are not stable. On the other hand, we show that the deuteration of the is always reversible because precursors to silicon etching are scarce on the surface. Then, we demonstrate that hydrogen (deuterium) adsorption at 300 K on both the (buffer-layer) and the quasi-free-standing graphene occurs on carbon atoms justifying their carbon-rich appellation. Comparison of the deuterium binding in the intercalation layer of quasi-free-standing graphene with the deuterated surface provides some indication on the bonding structure at the substrate intercalation layer. Finally, by measuring C-H (C-D) vibrational frequencies and hydrogen (deuterium) desorption temperatures we suggest that partial sp2-to-sp3 rehybridization occurs for the carbon atoms of the buffer-layer because of the corrugation related to covalent bonding to the SiC substrate. In contrast, on quasi-free-standing graphene hydrogen (deuterium) atoms adsorb similarly to what is observed on graphite, i.e. without preferential sticking related to the underlying SiC substrate
Electronic structure of tetra(4-aminophenyl)porphyrin studied by photoemission, UV–Vis spectroscopy and density functional theory
The valence and conduction bands of a thin film of tetra(4-aminophenyl)porphyrin (TAPP) are investi-gated by direct and inverse photoemission as well as by comparison to density functional theory (DFT)calculations. By projecting the electronic eigenfunctions onto the molecular framework it was possibleto interpret the origin of each spectroscopic feature. Although the majority of the photoemission spec-trum is attributed to the unsubstituted tetraphenylporphyrin (TPP) parent molecule, several featuresare clearly due to the amino substitution. Substitution also has important consequences for the energypositions of the frontier orbitals and therefore on the low-energy electronic excitations. The measuredelectronic transport energy gap (Eg= 1.85 eV) between the highest occupied molecular orbital (HOMO)and lowest unoccupied (LUMO) in TAPP is found to be significantly reduced with respect to TPP. More-over, an increased energy separation between the two highest occupied states (HOMO and HOMO−1) isfound both experimentally and by DFT calculations. Such evidence is attributed to an increased HOMOorbital destabilization due to an enhanced electron-donor character of the phenyl substituents uponamino functionalization. Finally, the above findings together with further time-dependent DFT calcula-tions are used to interpret the effect of the amino groups on the UV–Vis absorption spectrum, namely anoverall red-shift of the spectrum and remarkable intensity changes within the Q band.© 2017 Elsevier B.V
Etude par photoémission de la structure électronique des oxydes d'étain purs et partiellement réduits
Etude des effets de corrélation aux surfaces et interfaces de semiconducteurs par spectroscopie de photoémission inverse
AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF