Wu Sicheng

Electronic structure of Sn-doped C60 film

Abstract The Sn-doped C 60 film was obtained by annealing a 100A˚thick C 60 film with 6A˚thick Sn overlayer at 200°C. Photoelectron spectra show that the ration of Sn atoms to C 60 molecules in the film is about 3:1. The valence band and C 1s core level spectra of the Sn-doped C 60 film are similar to that of C 60 film. In contrast with the expectation of the reported superconductive phase of Sn- doped C 60 , no metallic conduction band with a distinct Fermi level cutoff has been observed in the valence bands portion.

Atomic and Electronic Structures of Submonolayer In on Cu(111)

We have studied the atomic and electronic structures of submonolayer In on Cu(111) using synchrotron radiation photoemission and scanning tunnelling microscopy. At very low coverage, In atoms were favourable to occupy substitutional sites and to be distributed evenly on the Cu(111) surface. At a higher coverage of 0.33 and 0.50 ML, two ordered reconstructed phases of ((3)1/2×(3)1/2)R30o and (2×1) have been observed for the first time. The two-dimensional states of In-induced valence bands in the ((3)1/2×(3)1/2)R30o phase were measured by angle-resolved photoemission. The result is in good agreement with theoretical calculations.

Pb Surfactant-Assisted Co Film Growth on Cu (111)

Surfactant-assisted Co film epitaxy growth on Cu (111) using Pb as a surfactant was studied by means of Auger electron spectra and synchrotron radiation photoemission spectra. The results reveal that with increasing the Co thickness most of the Pb atoms always float on the surface. Compared with 0.7 ML (monolayer) Pb, the Co film with 1.5 ML Pb surfactant has more layer-by-layer growth on Cu (111). The predeposited Pb layer can suppress the intralayer diffusion on the Cu (111) surface and effectively increase the Co island density at the initial stage of Co growth. On the contrary, a Pb-Co surface alloy was found during the Co film growth; this may hinder the interlayer diffusion of the deposited Co atoms, which is unfavorable to the layer-by-layer growth. The Pb-Co is also considered to be the main reason why some Pb atoms have been buried in the Co films.

Different interdiffusion characteristics between Ag/YBa2Cu3O7−x and Al/YBa2Cu3O7−x contact interfaces

Abstract The differences between the interdiffusion characteristics of Ag YBa 2 Cu 3 O 7−x and Al YBa 2 Cu 3 O 7−x contact interfaces have been revealed by secondary ion mass spectrometry (SIMS). The different electrical properties of Ag YBa 2 Cu 3 O 7−x and YBa2Cu3O7−x films after high temperature treatment are well understood by the SIMS results.

Plasmon Excitation in 2D and 3D C60 Studied by Photoemission

For near monolayer (ML) C60 condensed on Sn substrate, x-ray photoemission studies of C1s level reveal a feature centered about 22eV below the main peak. Analyses show that the feature is caused by the plasmon loss of the two dimensional C60 film. Bulk plasmon loss peak (similar 28eV blow the main peak), which has been observed on thick C60 films, was not observed on the C60 films with coverage θ < 2 ML. It indicates that the 28eV energy loss feature is due to a bulk plasmon associated with the solid C60 but not a single C60 molecule.

Valence band photoemission behavior of Pr1-xSrxMnO3

Valence band photoemission experiments on Pr1-xSrxMnO3 polycrystalline system with x ranging from 0.0 to 0.4 show that the density of states of the bands appearing in the ranges between Fermi level and similar to 12 eV below Fermi level have a substantial change with the doping level x. These features are discussed in terms of charge transfer in the ground states of Pr1-xSrxMnO3 system. A nonlinear charge transfer with the doping amount x is evidenced and a possible second order phase transition mediated by the charge transfer is proposed

Surface State at bar K Point of Surface Brillouin Zone on Cu{111} Surface

Electronic structure of Cu{111} surface along - line of surface Brillouin zone (SBZ) was studied using synchrotron radiation angle-resolved photoemission. A surface state located at 3.0 eV below Fermi level, near point of SBZ was observed for the first time. It is described by localized d-electron Tamm surface state.

Electron Band Structure of C60 Single Crystal Using Synchrotron Radiation

Electron band structure of C60 single crystal has been investigated using synchrotron radiation. On the cleaved (111) surface of the C60 single crystal the angle-resolved ultraviolet photoelectron spectra were measured at normal emission with varying photon energy from 12.7 to 28.2 eV. The valence band dispersions in L-Γ-L direction were successfully observed. The dispersions are 0.14 and 0.17 eV for the highest occupied molecular orbitals (HOMO) and HOMO-1 derived band respectively.

Development of Valence Bands of C60 from Submonolayer to Two and Three Dimensionality

For submonolayer amounts of C60 condensed on Sn substrate, the peaks derived from top two occupied molecular orbitals were broadened by 0.3 eV in comparison with solid C60. For coverage θ < 1 monolayer, the broadenings are independent of the coverage. It indicates that the delocalizations of electrons in valence bands of C60 are weak and the widths do not reflect the true band dispersions.

Adsorption of Oxygen on KxC60 Studied by Photoelectron Spectroscopy

Photoemission spectra of vacuum deposited K-incorporated C60–KxC60 (x ≈ 6), before and after exposure to oxygen, show that the interaction between oxygen and potassium forms an overlayer of 40 A K-O complex with stoichiometry near to that of potassium peroxide K2O2 on the surface. In contrary to the oxidation of potassium film, no potassium oxide K2O has been observed.