Xu Ya-Bo

Electrical conductivity studies of a pure C60 single crystal

Single crystals free from solvent up to millimetre size were grown. The temperature dependence of the electrical conductivity of a C60 single crystal was reported. A sharp decrease in conductivity related to the phase transition at 251 K was confirmed. A drop in the activation energy of around 274 K was observed for the first time. This activation energy drop suggests that the rotational dynamics of the C60 molecule above 251 K are more complex than the uncorrelated diffusion reported by Neumann et al.

Evidence for Local Interaction of Cs and CO on Ru(0001)

Ultra-violet photoemission spectroscopy measurements for CO adsorption on the (2×2)-Cs precovered Ru (0001) surface were performed. The Cs 5p (5p3/2) level (Cs state) locates at 11.3 eV in binding energy for the (2×2)-Cs overlayer on Ru (0001). Upon the CO adsorption, a new peak, which is associated with the Cs 5p state for the Cs adatoms influenced by the neighbouring CO adsorbed (the Cs+CO state), appears at the lower binding energy side of the Cs state. This new peak is at 10.8 eV for the CO saturation where the (2×2)-Cs+2CO compound layer is formed. This result gives clear evidence for local interaction of Cs and CO on the Ru (0001) surface. PACS: 73. 20. At, 82. 65. My, 68. 35. Bs

Anomaly of high temperature conductivity on C60 single crystal

Abstract The anomalous conductivity behavior in high temperature of a C 60 single crystal is reported for the first time in this paper. The results showed an anomaly of the conductivity above 425 K. Two mechanisms which may be responsible for this anomaly have been discussed. Moreover, this anomaly found may be instructive to the growth of C 60 single crystal.

Electronic Structure of Eu6C60

We study the valence band of Eu-intercalated C60 by synchrotron radiation photoelectron spectroscopy to understand the ferromagnetism (FM) and the giant magnetoresistance (GMR) of Eu6C60. The results reveal the semiconducting property and the remarkable 5d6s-π hybridization. Eu-C60 bonding has both ionic and covalent contributions. No more than half the 5d6s electrons transfer from Eu to the LUMO derived band of C60, and the LUMO+1 derived band is not filled. The remaining valence electrons of Eu, together with some π (LUMO, HOMO and HOMO-1) electrons, constitute the covalent bond. The electronic structure implies that the magnetic coupling in Eu6C60 should be through the intra-atomic f-sd exchange and the medium of the π electrons. The possibility of the GMR being tunnelling magnetoresistance is ruled out.

Angle-resolved UPS investigation of co-adsorption of CO and K on Fe(110) surface

A symmetry plane for K-CO co-adsorbate at low coverage on Fe(110) surface was found using angle-resolved UPS with polarized light. This plane is parallel to the 110 azimuth of the crystal surface. The dependence of the CO 4σ peak intensity on incidence angle was found to be nearly the same as in the case without K, where the molecular axis of CO is perpendicular to the surface.

Preparation and photoemission spectra of Rb3C60 single-crystal thin films

Rb3C60 single-crystal thin films were prepared on the cleaved (111) surface of C60 single crystal. The photoemission spectrum line shapes of the lowest unoccupied molecular orbital (LUMO) derived band at room temperature and 150 K were established by synchrotron radiation photoemission spectrum measurements. The density of states near the Fermi level was distinctly affected by temperature. No less than six sub-peaks of the LUMO band were observed even at room temperature. The existence of so many sub-peaks offered the opportunities to analyse in more detail the orientational structure and the electron-Boson interactions of the narrow-band metallic Rb3C60.

Study of the reactivity of surface oxygen species on SmMnO3 and SmFeO3 catalysts

Abstract The reactivities of surface oxygen species of SmMnO 3 and SmFeO 3 were determined by the thermodesorption spectroscopy method. They show quite different reactivities.

Residual compressive stress and intensity of infrared absorption of cubic BN films prepared by plasma enhanced chemical vapor deposition

Theoretical and experimental investigations on the dependence of the intensity of infrared (IR) absorption of polycrystalline cubic boron nitride thin films under the residual compressive stress conditions have been performed. Our results indicate that the intensity of the IR absorption is proportional to the total degree of freedom of all the ions in the ordered regions. The reduction of interstitial Ar atom concentration, which causes the increase in the ordered regions of cubic boron nitride (cBN) crystallites, could be one cause for the increase in the intensity of IR absorption after residual compressive stress relaxation. Theoretical derivation is in good agreement with the experimental results concerning the IR absorption intensity and the Ar interstitial atom concentration in cubic boron nitride films measured by energy dispersion X-ray spectroscopy. Our results also suggest that the interstitial Ar is the origin of residual compressive stress accumulation in plasma enhanced cBN film deposition.

Synchrotron radiation photoemission spectrum study on K 3 C 60 film

K3C60, single crystal film was prepared on the cleaved (111) surface of C60, single crystal. Synchrotron radiation angle-resolved photoemission spectra were measured at normal emission with sample temperature at × 150K. Up to four subpeaks of LUMO-derived band were observed. These sub-peaks exhibit distinct energy dispersions which resemble in general the theoretical ones calculated for K3C60 at low temperature with the so-called one-dimensional disordered structure. But there is large deviation of experimental sub-band intervals from the theoretical values. This result is meaningful for the studies of the physical properties of alkali-doped C60 solids, e.g. the mechanism for superconductivity.

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.