Shojun Hino

Ultraviolet photoelectron spectra of C84 and KxC84

Abstract Ultraviolet photoelectron spectra of C 84 , one of the fullerene family compounds, and of potassium-dosed C 84 have been measured with synchrotron radiation. The spectra of C 84 are compared with those of C 60 and C 70 . The photoemission spectral onset of C 84 is 1.3 eV below the Fermi level, which is smaller by 0.5 eV than that of C 60 or C 70 . This indicates its small band gap, which was expected from its absorption spectra. Upon potassium dosing, a new band becomes distinct between the Fermi level and the highest occupied molecular orbital band. The new band edge does not cross the Fermi level, which indicates that potassium-dosed C 84 is not metallic but a semiconductor.

Ultraviolet photoelectron spectra of C76 and KxC76

Abstract Ultraviolet photoelectron spectra of C76, one of the fullerene family of compounds, have been measured with a synchroton radiation light source. The photoemission spectral onset is 1.3 eV below the Fermi level, which is equal to that of C84 but is about 0.5 eV smaller than that of C60 or C70. The relative intensity of the photoemission spectral features is independent of the incident photon energy change. Photoemission spectral changes for C76 during potassium dosing are also measured. A new band becomes distinct between the Fermi level and the HOMO band, when the potassium content (x in KxC76) is equal to or greater than 1.1. The spectral onset moves toward the Fermi level with increasing potassium dosage, approaching it but never crossing it. This indicates that potassium-dosed C76 could be a narrow gap semiconductor.

Comparative photoemission study of RbxC60, RbxC70 and RbC8. A pseudo-gap at the Fermi level in the fulleride

Abstract A comparative photoemission study on RbxC60, RbxC70 and RbC8 (graphite intercalation compound) is reported. It was found that the Fermi level of Rb3C60 is located at the bottom of a valley of the density of states, while that of RbC8 is at a maximum point of the occupied states. This experimental result is explained in terms of the existence of a pseudo-gap at the Fermi level in the fulleride. This indicates that a rigid-band picture is not a good starting point for understanding the change of the electronic structure upon the alkaline-doping. It was also found that the density of states at the Fermi level is much smaller in RbxC70 than in RbxC60. This accounts for the less conductive nature and the absence of superconductivity in RbxC70.

Dimeric and trimeric tetrathiafulvalenes with strong intramolecular interactions in the oxidized states.

New dimeric and trimeric TTF derivatives with methylenedithio spacers (1a,b, 2a, and 2b) have been synthesized. X-ray structure analysis revealed that TTF units of the dimer 1b adopted distorted face-to-face overlapping arrangement both in intra- and intermolecular stacking. Cyclic voltammetric study indicated that trimeric 2a was in favor of taking di- and tetracationic states, while the dimeric 1a was in favor of taking a monocation. The absorption spectroscopic study suggested an existence of the strong face-to-face interaction particularly in di-, tri-, and tetracationic state of the trimeric TTF derivatives.

Potassium-oxygen graphite intercalation compounds

Abstract Intercalation of potassium superoxide KO 2 into graphite in the presence of potassium metal was studied. Graphite intercalation compounds of stage 1 (assigned formula C 4 KO 2 , c -axis repeat distance 8.44 A) and stage 2 (assigned formula C 8 KO 2 , c -axis repeat distance 11.75 A) were synthesized and isolated for the first time. A quadruple intercalate layer KOOK is supposed. In-plane structure of the intercalate layer is discussed mostly on the basis of X-ray diffraction intensity analysis and transmission electron microscopy electron diffraction. A metal-like temperature dependence of c -axis resistivity was obtained in the 1.5–300 K temperature range where the resistivity values at room temperature are 0.07 and 0.81 Ω cm for stage-1 and stage-2 compounds, respectively. The results of magnetic susceptibility measurements suggest that the oxygen species are in nonmagnetic states.

Fabrication of field-effect transistor devices with fullerodendron by solution process

n-channel field-effect transistor (FET) devices have been fabricated with thin films of fullerodendron on SiO2∕Si, polyimide/Au/poly(ethylene terephthalate), and polyvinyl alcohol/Au/poly(ethylene terephthalate) substrates by using solution processes. The value of field-effect mobility μ of the fullerodendron FET reaches 1.7×10−3cm2V−1s−1 at 300K. The mobility gap and optical gap have been estimated to be 0.15 and 1.4eV, respectively. The channel conduction in the FET device follows thermally activated hopping-transport mechanism below 300K.

Ultraviolet photoelectron spectra of electropolymerized polymers: polyazulene, polypyrene and polycarbazole☆

Abstract Ultraviolet photoelectron spectra (UPS) of electrochemically synthesized conducting polymers, polyazulene, polypyrene and polycarbozole, are measured. When the polymers are doped with either ClO4− or BF4−, the spectral onsets move toward the Fermi level (EF), which is related to an improvement of the electric conductivity upon doping. As the bandgaps of both doped polycarbazole and polypyrene estimated from UPS are more than 1 eV, their expected conductivities are poor. On the other hand, doped polyazulene gives virtually 0 eV bandgap, which agrees well with its reported high conductivity. UPS of polycarbazole and polypyrene correspond with those of gaseous carbazole and pyrene, respectively, which suggests a small interaction between the monomer molecules in these polymers. UPS of polyazulene and azulene show poor correspondence, which indicates a strong interaction between the azulene units in the polymer. The difference between these two groups is discussed from the point of view of molecular conformation derived from steric hindrance.

Electronic structures of cumulene type carbyne model compounds: a typical example of one-dimensional quantum well

Ultraviolet photoelectron spectra of linear chain cumulene type carbyne model compounds with phenyl terminal groups to stabilize the chain have been measured and assigned with semi-empirical molecular orbital (MO) calculation. The spectra can be basically divided into two parts; contributions from phenyl groups and the chain part. The longer the chain length becomes, the lower the binding energy of the highest occupied molecular orbital (HOMO). The MO calculation reveals that the HOMO of these compounds derives from the carbon chain part and supports experimental results on chain length dependence of the HOMO. The HOMO and the lowest unoccupied molecular orbital (LUMO) of the model compounds are considered in terms of one-dimensional quantum well.

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.

Photoemission study of C60 and its alkali-metal compounds

Abstract Photoemission spectroscopy was performed for solid C60 and its alkali-metal(K and Rb) compounds produced by successive vapor-deposition of alkali metal (K or Rb) on an evaporated C60 film. A series of photoemision spectra show a unique variation against the alkali-metal content which is not explained in terms of a simple band-filing picture with alkali s electrons. The correlation between the photoemission spectra and the electrical resistivity of the film was also studied.