D. M. Poirier

Electron stimulated polymerization of solid C60

Electron‐stimulated modifications to pure C60 films grown on GaAs(110) have been induced by ∼3 eV electrons from a scanning tunneling microscope (STM) and from 1500 eV electrons from an electron gun. In the STM‐modified area, a variety of apparent molecular sizes and shapes were observed with intramolecular contrast and a blurring of intermolecular distinction. Surfaces bombarded by 1500 eV electrons showed modifications over larger areas and these results suggested a growth mode for polymerization. Annealing of such modified surfaces restored the ordered fcc structure.

Formation of fullerides and fullerene-based heterostructures.

Two potassium fulleride phases, metallic K3C60 and nonmetallic K6C60, are formed when potassium is incorporated into thin C60 films under ultrahigh vacuum conditions. Phase separation is observed for intermediate stoichiometries. Results obtained for the C60-K3C60 heterostructure demonstrate that it is stable against potassium migration from the K3C60 phase. In contrast, the C60-K6C60 interface is not stable and K3C60 is formed.

Occupied and unoccupied electronic states of solid C70 with comparison to C60

Abstract The distribution of the valence and conduction band electronic states of solid C70 have been studied with synchrotron radiation photoemission and inverse photoemission. The results show 16 features in the valence band and 10 in the conduction band. The s- and p-character of these states is identified, with those closest to the Fermi level being attributed to pπ-derived levels. Comparison to results for C60 shows differences due to molecular symmetry and configurational disorder of the solid.

Solid State Properties of Fullerenes and Fullerene-Based Materials

Publisher Summary This chapter provides an introduction of fullerenes by comparing gas phase and solid state properties, examining thin film and bulk crystal growth, and doping with alkali metals and other atoms. The fullerenes are all-carbon molecules with a closed-cage structure and nearly spherical appearance. These cages are derived from 12 pentagons and an appropriate number of hexagons. The chapter also discusses the electronic structure of correlated-electron systems in fullerenes, relating the electronic properties and vibrational properties to superconductivity. Early descriptions of fullerene formation suggested that small carbon chains would grow by the sequential addition of carbon radicals. Finally, the chapter discusses the latest additions to the fullerene family—namely, endofullerenes, tubes, and the buckyonions.

KxC60 : nonequilibrium thin film growth and spectroscopic results

Abstract This paper examines the electronic structure of the K-C 60 system. High resolution photoemission results show multiple phase formation, even for stoichiometries close to nominal single phase fields. The results are interpreted in terms of the nonequilibrium conditions for growth by vapor phase deposition.

Isolation of fulleride phases by distillation

A technique for the synthesis of phase pure alkali‐metal fullerides is demonstrated. The fulleride compounds are distilled from mixed phase samples or from other pure phases by the preferential evaporation of either fullerenes or alkali‐metal atoms. Distillation has been used to form K3C60, K4C60, RbC60, and Rb4C60 which exhibit core level photoemission spectra that are consistent with bulk structure measurements. The KxC70 system, for which structural information has not been reported, was also examined and the compounds KC70, K3C70, and K4C70 were found.

KxC60 Structural evolution: Scanning tunneling microscopy and low energy electron diffraction

Abstract Epitaxial films of C 60 were grown on GaAs (110), doped with K. under ultrahigh vacuum conditions, and studied using scanning tunneling microscopy and low energy electron diffraction. C 60 condensation at 470 K resulted in the growth of commensurate c (2 × 4) islands that converted to a two-domain, incommensurate close-packed structure by one monolayer. This close-packed layer acted as a template for layer-by-layer growth of fcc C 60 . The resulting multilayer films exposed nearly defect-free (111) surfaces when deposition was done at elevated temperature. When doped with K, these crystalline thin films maintained their fcc structure until x = 3. When x exceeded 3, the films transformed to body-centered structures and exposed (110) surfaces. The K 60 C 60 , phase exhibited a multi-domain bcc (110) surface with bcc [001] aligned with close-packed directions of the original fcc (111) surface, i.e. fcc [110]. This is consistent with lattice stretching along one of the three equivalent fcc (111) close-packed directions to achieve the transformation. Potassium doping was also accompanied by an increase in the surface vacancy concentration and a reduction in structural quality.

K-C60:Growth Structures, Phase Formation, and Electronic Properties

This paper focuses on K-C60 thin films. Scanning tunneling microscopy shows that high quality films can be grown epitaxially on GaAs(110), ultraviolet photoemission shows the complex nature of the electronic states of the K3C60 phase, and x-ray photoemission reveals the phase diagram for this system.