Electronic structure of fullerene and alkali-fulleride films

Miscellaneous · Fri Jan 01 00:00:00 EST 1993

OSTI ID:7112255

Benning, P J

Photoemission and inverse photoemission spectroscopy have been used with low energy electron diffraction (LEED) and resistivity measurements to examine the electronic structure, transport properties, and crystallinity of A[sub x]C[sub 60] thin films where A = Na, K, Rb, and Cs and 0 [le] x [le] 6. These measurements demonstrate the highly molecular character of fullerene and fulleride films. For undoped C[sub 60] films, temperature dependent LEED studies show changes that correspond to the lattice transformation from the simple cubic to the face centered cubic structure. For doped C[sub 60] films, the LEED results show a decrease in the quality of the LEED pattern upon the nucleation of the body-centered A-C[sub 60] phases. Alkali doping produces changes in the emission spectra that can be related to the occupation of bands derived from the lowest unoccupied molecular orbital of the fullerenes. The effects of electron correlation are important in each fulleride phase. The A[sub 1]C[sub 60] phases of Rb and Cs are characterized by an occupied valence band feature that is [approximately]0.5 eV wide centered [approximately]0.25 eV below E[sub F] derived from the lowest unoccupied molecular orbitals (LUMO) of C[sub 60]. For these phases there is also emission at the Fermi level. The A[sub 3]C[sub 60] phase of K and Rb exhibit a metallic Fermi level cutoff. Spectroscopic features 0.3 and 0.7 eV below E[sub F] are observed that are not reproduced in one-electron band structure calculations. The A[sub 4]C[sub 60] phases of K, Rb, and Cs all exhibit insulating character with a split LUMO band. All of the A[sub 4]C[sub 60] phases are insulators with a filled LUMO band. For Na-C[sub 60], the valence band spectra show no emission at E[sub F] for any Na concentration. Resistivity measurements for K[sub x]C[sub 60] show a resistivity minimum for K[sub 3]C[sub 60] and a dependence on stoichiometry indicative of dispersed conducting micrograins in an insulating medium.

• Research Organization: Minnesota Univ., Minneapolis, MN (United States)
• OSTI ID: 7112255
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
36 MATERIALS SCIENCE
ALKALI METAL COMPOUNDS
CRYSTAL STRUCTURE
ELECTRIC CONDUCTIVITY
ELECTRONIC STRUCTURE
FULLERENES
CRYSTAL DOPING
CRYSTAL-PHASE TRANSFORMATIONS
ELECTRON DIFFRACTION
PHOTOEMISSION
TEMPERATURE DEPENDENCE
CARBON
COHERENT SCATTERING
DIFFRACTION
ELECTRICAL PROPERTIES
ELEMENTS
EMISSION
NONMETALS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SCATTERING
SECONDARY EMISSION
664500* - Special Atoms & Molecules- (1992-)
360600 - Other Materials