T. Moriwaki

Isolation and identification of fullerene family: C76, C78, C82, C84, C90 and C96

Abstract A preparative high-performance liquid chromatography was examined for the isolation of higher fullerenes from CS 2 extracts of the carbon soot produced by arc heating of graphite in inert atmosphere. At least eight all-carbon compounds C 60 , C 70 , C 76 , C 78 , C 82 , C 84 , C 90 and C 96 were confirmed as a “stable fullerene”. C 82 and C 96 are new members of fullerene family which have not been reported so far. The presence of stable C 82 seems to be closely related with the recent su macroscopic quantities of production of LaC 82 reported by Smalleys group.

Neutral carbon cluster distribution upon laser vaporization

The mass distribution of neutral carbon clusters generated by a laser vaporization of graphite in He was safely determined by a single photon (10.5 eV) ionization technique. The resulting mass distribution was surprisingly different from those reported in previous articles. It was found that the carbon clusters generated under a moderate laser fluence condition (0.1–1 J/cm2) consists of mostly even-numbered monocyclic rings with the cluster sizes of n=10–18. The formation mechanism of such neutral carbon clusters upon laser irradiation is discussed.The mass distribution of neutral carbon clusters generated by a laser vaporization of graphite in He was safely determined by a single photon (10.5 eV) ionization technique. The resulting mass distribution was surprisingly different from those reported in previous articles. It was found that the carbon clusters generated under a moderate laser fluence condition (0.1–1 J/cm2) consists of mostly even-numbered monocyclic rings with the cluster sizes of n=10–18. The formation mechanism of such neutral carbon clusters upon laser irradiation is discussed.

Ultraviolet photoelectron spectroscopy on the linear conformer of negatively charged carbon clusters Cn− (10≤n≤16)

Abstract A photoelectron spectroscopy technique was successfully applied to the detection and characterization of a linear conformer of negatively-charged carbon clusters from C10− to C16−. By controlling the laser fluence for vaporization it was found that the fraction of a linear conformer was enriched. The presence of the linear form up to C16− was confirmed by the photoelectron spectroscopic evidences. On the basis of the present observations, it was also found that the observed vertical electron affinity up to C16 shows a distinct even–odd alternation, converging into the asymptotic value of ca. 5.0 eV.

A hypothetical growth mechanism of carbon five- and six-membered ring networks

Abstract One of the most prominent aspects of the novel form of carbon molecules, the “fullerenes”, is the characteristic features of the CC bond networks. The fullerene hollow closed cage consists of five- and six-membered rings, providing a spherical surface with no adjacent pentagons in the network (isolated pentagon rule, IPR). Here we describe a novel picture of growth of fullerenes, paying special attention to the initial stage of growth of five- and six-membered ring networks. Some important precursors associated with specific fullerenes are suggested in connection with the structure and stability of small carbon clusters.

Evidence of linear chain forn≧10 carbon negative ion clusters revealed by mass selected photodetachment spectroscopy

Photodetachment spectra of negative carbon clusters are reported in the size range from 5 through 20 atoms. The clusters were prepared in a supersonic beam by laser vaporization and 2nd (2.3 eV) and 3rd (3.5 eV) harmonics of Nd-YAG laser were used for photodetachment. The resultant data indicate that carbon negative cluster ions in the 10–20 range take the forms of both linear chain and cyclic ring under a certain condition.

Dynamics of cluster-surface interaction: Evidence of structural isomers of C60−

Collision induced electron detachment of the fullerene C60− and the other C60− produced through the laser vaporization of a carbon rod was studied. Both of C60− showed quite different behavior for the process. It was suggested that the laser vaporized C60− has a different structure from the fullerence C60−.

Collisional electron emission at solid surfaces induced by mass selected negative cluster ions

Electron emission efficiency induced by the collision of clusters with a solid surface was measured as a function of cluster size. Emitted electron energy distribution for the impact of mass selected negative ion clusters or mass selected neutral clusters was also measured in the energy region of 0–5 eV. The difference in the shape of the electron spectra was observed depending on the size and charge of the clusters.

Threshold electron spectra of semiconductor cluster ions

A simple threshold electron analyzer was constructed and laser photodetachment threshold electron spectra of Si− and Si4− were measured.

Size- and state-selected cluster chemistry

New aspects of size- and state-specific properties of carbon cluster are described on the basis of experimental evidences obtained by recently developed clusterbeam apparatus. The present paper consists of mainly two topics. One of which is spin states for small carbon neutral clusters. Focusing effects induced by a hexapole magnetic field were examined for the carbon clusters from C1 to C6. The second is the study of cluster-solid surface interactions. Electron emission processes induced by collision of negative cluster ions with M0S2 single crystal were investigated in detail, paying special attention on the electron emission efficiency as functions of both size and incident kinetic energy. A new collision induced phenomenon has been found, which may be closely related with an electron detachment of negative ions induced by a surface potential of the solid target.

Dynamics of the Cluster-Surface Interaction: Collisional Detachment of Size Selected Carbon Negative Cluster Ions

Size selected carbon negative cluster ions (n = 5−22, 60, and 70) were examined on the collisional electron emission at solid surface as a function of the incident kinetic energy (0–1keV). Two different mechanisms were found below 1 KeV collision energy. Electron emission occurring at high energy ( > 300 eV) is totally governed by velocity of the incoming cluster ions. The electron emission at the low collision energy, on the other hand, is considerably dependent on the molecular structures of the carbon clusters, i.e., linear chain, monocyclic ring, and hollowclosed-cage structures. The latter process is a new phenomenon which may be closely related with a collisional electron detachment of negative cluster ions.