Abstract
Electronic structures of C 60 polymer crystals (dimerized C 60: dimer-C 60, one-dimensionally polymerized C 60: 1D-C 60 and two-dimensionally polymerized C 60: 2D-C 60) were studied by using a high energy-resolution electron energy-loss spectroscopy microscope. Spectra were obtained from single crystalline specimen areas of 180 nm in diameter. The dielectric functions of the materials were derived from valence electron excitation spectra by using Kramers–Kronig analysis. The onset energies of the imaginary parts of the dielectric functions ɛ 2 (bandgap energies) were 1.6 eV (dimer-C 60), 1.4 eV (1D-C 60) and 1.5 eV (2D-C 60). Those energies are smaller than that of the monomer C 60 (mono-C 60) crystal of 1.7 eV. Energies of interband transition peaks observed in each ɛ 2 of polymerized C 60 material were smaller by amounts of 0.5 eV than those of corresponding peak energies of mono-C 60. Excitation spectra of 1s electrons to the conduction band showed that the intensity of 1s → π * transitions compared to that of 1s → σ* transitions was smaller than that of mono-C 60. It may due to that a part of π-bonds of a C 60 cluster changed to σ-bonds to form covalent bonds with neighboring C 60 clusters in the polymerization process.
Published Version
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