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The effect of hydrogenation on the conduction bands of the Si-rich 6H-SiC(0001)-(3×3) reconstruction is studied using inverse photoemission spectroscopy in order to distinguish surface from bulk states. These results are exploited for the comparative study of the interaction of C60 adsorbed on (3×3) and on hydrogen-terminated (3×3). For the latter, as in the case of hydrogen-terminated Si, C60 is electronically decoupled from the substrate. Upon annealing a C60 thick film deposited on hydrogenated (3×3) up to 670 K, there is a hint for a possible hydrogen transfer to the C60 molecules. The initially physisorbed molecules then adopt covalent bonding with Si, forming the contact layer. Part of the substrate is already found uncovered at this temperature. By further annealing up to 860 K all H atoms have desorbed. Finally, at 1100 K the remaining covalently bound C60 have desorbed. Unexpectedly, the structural damages caused by H and C60 deposition and by the successive annealing steps do not prevent a final restoration of the initial (3×3) reconstruction at about 1100 K.

The desorption or fragmentation temperature of C-60 bound to Si-rich-(3 x 3) and (root 3 x root 3) R30 degrees. reconstructions of 6H-SiC(0001) is investigated using inverse photoemission spectroscopy (IPES) and LEED experiments. On SiC-(3 x 3), C-60 film is found desorbed after annealing at a high temperature of 1140 K, supporting covalent bonding. Meanwhile, the Si tetramers of the (3 x 3) nanostructured substrate are recovered, as can be inferred from the full reappearance of the Mott-Hubbard surface state in the IPE spectra. SiC-(3 x 3) behaves in a singular way among the other semiconducting substrates, which covalently bind to C-60. This remarkable feature is attributed to the low density of Si dangling bonds and to the highly corrugated character of this reconstruction.

International audience; Using angle-resolved inverse photoemission spectroscopy (KRIPES), we have investigated the unoccupied electronic structure of the model interface Sn/Si(1 1 1)-a-  3 p at room temperature. In addition to a ``metallic'' surface state crossing the Fermi level (E F) near the K H point, we unambiguously assign a second feature of our KRIPES spectra, located around 1.5 eV above E F , to a second surface state U H 2. We will experimentally show that U H 2 is an intrinsic feature of the a-  3 p reconstruction which cannot be associated with defects. The existence of these two surface states is not compatible with the ideal T 4 model which would show either a single, half-occupied metallic band crossing E F , or an insulating phase if strong correlation effects, important for these narrow surface bands, are considered. Rather, both U H 1 and U H 2 receive a natural explanation, once many-body effects are introduced, in the framework of a dynamical ¯uctuations model, where two kinds of Sn adatoms sites reminiscent of a low-temperature 3  3 phase do persist at room temperature. Correlated surface bands incorporating many-body effects in a non restricted way provide a complete description of the experimental surface bands and their dispersions. #

International audience; This work presents a detailed comparison of the electronic properties of two phases a and g. of the prototypicalSi111.–'3 ='3 –Sn system, focussing on the empty surface states. The latter reconstruction has been studied at roomtemperature with inverse photoemission KRIPES.. For the g-phase characterised by an equal amount of Sn and Si adatoms,a charge transfer towards the Sn adatom leaves an empty surface state localised on Si adatoms, and observed in KRIPES 0.4eV above the Fermi level EF. at the surface Brillouin zone SBZ. center. The band gap of this semiconducting g-phase isestimated around 0.5 eV. In contrast, the a phase with only Sn adatoms shows a metallic behaviour and two distinctadatom-derived empty surface states.

Three-dimensional unoccupied band structure of graphite : very-low-energy electron diffraction and band calculations / R. Claessen ... - In: Physical review. B. 61. 2000. S. 4994-5001

Physical review / B 42(18), 11914 - 11925 (1990). doi:10.1103/PhysRevB.42.11914, The electronic properties of tin dioxide single-crystalline (110) surfaces have been studied in correlation with their structure by low-energy electron diffraction, angle-integrated and resonant photoemission using synchrotron radiation [ultraviolet photoemission spectroscopy (UPS)]. Energy distribution curves were measured from the Sn 4d core levels and from the valence band. The experimental valence band is compared with the theoretical density of states (DOS) from perfect and defective surfaces. UPS difference curves, normalized to the Sn 4d intensity, reflect mainly the increase in the oxygen partial DOS when the sample is annealed at increasing temperatures up to 1000 K after sputtering. Their comparison with simulated theoretical difference curves favors a bridging oxygen termination for annealing temperatures above 900 K. After argon-ion bombardment, band-gap defect states that are not predicted by the calculations are found at a maximum density 1.4 eV above the valence-band maximum (VBM). Various degrees of resonant enhancement occur throughout the valence band when the photon energy crosses the Sn 4d→5p photoabsorption threshold, and these are used to establish the tin-derived character of the gap states, for which a tin 5s origin is proposed. Partial-yield spectra allow the localization of unoccupied Sn 5p states in the conduction band starting from 8 eV above the VBM with a maximum at 10 eV. The Sn 4d→5p absorption threshold also shows possible core exciton formation for sputtered surfaces only., Published by Inst., Woodbury, NY