Zhou Xihuang

Separation of C60 and C70 fullerenes in gram quantities by fractional crystallization

Abstract A simple and inexpensive method for the purification of gram quantities of >99.5% pure C60 and > 98% pure C70 by a fractional crystallization process in carbon disulfide or o-xylene is described. This process is based on the finding that C60 was enriched in the solid deposit, whereas C70 was enriched in the mother liquor during crystallization of fullerenes due to differential solubilities of these two fullerenes, C60 and C70, in these solvents.

Superconductivity in Sn-doped C60

Abstract The superconductivity has been detected in the Sn-doped C60 samples by AC susceptibility measurements. The Sn-doped C60 sample is insensitive to air. EDS and XRD examinations show that the Sn-atoms have intercalated into the interstitial positions of the C60 lattice during a very slow diffusion reaction process.

Superconductivity and structure of alkali-doped fullerenes : K3C60 and Rb3C60

The linearly polarized Cu L3-edge x-ray-absorption near-edge structure (XANES) of Bi2Sr2CaCu2O8 + delta has been measured and the spectra are interpreted by the full multiple-scattering approach in real space. The polarized spectra over a range of 20 eV can be predicted in terms of the one-electron dipole (DELTA-l = +1) transition Cu 2p --> epsilon-d, probing the unoccupied d-like (l = 2) density of states projected on the Cu site with orbital angular momentum m(l) = 0, 1 in the E parallel-to z spectra, and the m(l) = 2, 1, and 0 in the E perpendicular-to c spectra. The oscillator strength for the dipole allowed transitions (DELTA-l = -1) Cu 2p --> epsilon-s is shown to be a factor of 100 weaker than the 2p --> 3d transitions. The Coulomb interaction in the final state between the Cu 2p core hole and the excited Cu 3d electron is found to be 5.5 eV forming a bound state below the continuum threshold, the well-known Cu L3 white line. On the contrary, the core hole induces a nearly rigid redshift about 1 eV of the high-energy conduction bands.

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.

Photoemission Evidence for Dilute K-doped Phase KxC60 with x<0.2

A shift about 0.3eV to higher binding energy is reported in the valence band and C 1s core level of KxC60(x<0.2). Analysis shows that the result could not be interpreted by a mixture of C60 and K3C60. A dulite K-doped phase and fermi level pinning near the lowest unoccupied molecular orbital derived band caused by K-doping are proposed.