Kazunori Umishita

Ultraviolet photoelectron spectra of metallofullerenes, two Ca@C82 isomers

Abstract Ultraviolet photoelectron spectra (UPS) of two Ca@C 82 isomers (III and IV) were measured with a synchrotron radiation light source. The photoelectron onset energies of isomers III and IV were 0.7 and 0.8 eV below the Fermi level, respectively, which indicates their semiconductive nature. When the excitation energy is tuned, spectral intensity changes as other fullerenes have shown. Their upper valence band (0–5 eV) spectra are different from those of other metallofullerenes such as La@C 82 ,Sc@C 82 and Gd@C 82 as well as those of empty C 82 but their lower valence band spectra (below 5 eV) are almost identical. Comparison between the UPS and ab initio calculation assuming transfer of two electrons from encapsulated calcium atom to the cage (i.e. Ca +2 @C 82 2− ) suggests C 2 (c) geometry for isomer III and C s for isomer IV.

Ultraviolet photoelectron spectra of Sc@C82

Abstract Ultraviolet photoelectron spectra of the metallofullerene, Sc@C 82 are measured. The relative intensities of the band in the spectra varies with the incident photon energy change, as observed in other fullerenes. A difference spectrum between Sc@C 82 and C 82 shows two-peak components just below the Fermi level. Their intensity ratio suggests transfer of two electrons from the Sc atom to the fullerene cage.

Electrical conductivity and electronic structure of potassium doped PTCDA

Electric conductivity and ultraviolet photoelectron spectra (UPS) of potassium doped 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) were measured. The conductivity of potassium doped PTCDA film jumps up to 0.1 Scm -1 from around 10 -6 Scm -1 of pristine one. Potassium doping to PTCDA also brings change in the upper valence band UPS; spectral onset moves closer to the Fermi level (E F ). These phenomena can be attributed to electron transfer from potassium to PTCDA, which is confirmed by MNDO molecular orbital calculation.

Ultraviolet Photoelectron Spectra of Mono Metal Atom Encapsulated Fullerenes

Abstract Ultraviolet photoelectron spectra of mono metal atom encapsulated fullerenes, M@C82 (M = La, Gd and Sc), are measured with a synchrotron radiation light source. When the excitation energy is tuned, spectral intensity oscillation is observed in these mono metal atom encapsulated fullerenes as was in empty fullerene, C82. Their incident photon energy dependence is essentially the same. Their spectra deeper than 5 eV are almost identical and are similar to those of empty fullerene. The noticeable difference among the spectra is in the energy region between the Fermi level and 4 eV, which reveals the degree of electron transfer from the metal atom to the fullerene cage.

Photoelectron spectra of carbon materials containing multiwall carbon nanotubes

Ultraviolet and X-ray photoelectron spectra (UPS and XPS) of carbon materials prepared by dc arc discharge, containing multiwall carbon nanotubes (MWNTs) with high concentration, have been measured. UPS of a deposit produced on a graphite cathode have several peaks, which are observed clearly near the center of the deposit. Spectra are different between the specimens of MWNTs before and after purification. Comparison with results of other carbon materials exhibits that the spectra of MWNTs resemble that of graphite. These results indicate the variation of spectra induced by condition of alignment and direction of each MWNT in the specimen.

Ultraviolet photoelectron spectra of a higher fullerene C102 and its potassium complex

Abstract Ultraviolet photoelectron spectra of a higher fullerene C 102 has been measured with a synchrotron radiation light source. The photoelectron onset energy of pristine C 102 is 0.85 eV below the Fermi level ( E F ), which is the smallest value among the pristine fullerenes reported so far. The spectra show intensity oscillation upon the incident photon energy change as do those of other fullerenes. Spectral change upon potassium doping has been observed with the hv = 20 and 40eV incident photon energies. The 20 eV spectra reveal a formation of a new state between the E F and the band derived from the highest occupied molecular orbital (HOMO) upon potassium doping. The onset position of the new state moves toward the E F , but it does not cross the E F . This indicates the semiconductive nature of potassium doped C 102 . When the potassium is excessively doped to C 102 , the lower binding energy bands above 5 eV become faint. In accordance with this phenomenon, the hv = 40 eV spectra show an appearance of four distinct structures between 5 and 14 eV. As these bands are considered to derive from pseudo π-electrons, heavy potassium doping may correspond with reconstruction of the fullerene cage or decomposition of the cage structure.

Photoelectron spectra of metal fullerenes: Are metal fullerenes molecular crystals or not?

Ultraviolet photoelectron spectra (UPS) of GdC82 and La2C80 were measured using synchrotron radiation. The specimens for the measurement were not evaporated films but drying up films obtained from the metal fullerene solutions. Although the effect of the contamination to the specimens remains even after heat treatment, the UPS of the GdC82 film show several characteristic structures that are essentially identical to those of LaC82. This suggests that the interaction between the GdC82 molecules are small and GdC82 can be treated as a molecular crystal. The spectrum of La2C80 differs from those of other fullerenes, which indicates either that the interaction among the La2C80 molecules are too large to give a sharp spectrum or that the molecule does not have so-called cage structure.

Ultraviolet Photoelectron Spectra of Potassium Dosed Higher Fullerenes

Abstract Ultraviolet photoelectron spectra of potassium dosed higher fullerenes are measured with a synchrotron radiation light source. Potassium dosing to higher fullerenes brings a new structure between the spectral onset of pristine fullerenes and the Fermi level. As the spectral edge of the new structure does not cross the Fermi level, potassium dosed higher fullerenes are not metallic but semiconductive. When the potassium is excessively dosed to the fullerenes, the lower binding energy structures above 5 eV become faint. In contrast to this phenomenon, four distinct structures appear between 5 and 14 eV.