Structure and Electronic States of Carbon Onions

点击翻译按钮获取中文摘要

In this research project, we have performed a systematic study on the structure, and electronic states of carbon onions and carbon nanocapsules. Major results obtained are summarized as :1) Structure and electronic states of carbon onions : By annealing the nanodiamond particles 5nm in size in high vacuum, we could mass produce while spherical onions at around 1700℃ and polyhedral onions above 2100℃. Combining the results of high-resolution TEM, EELS, ESR, Raman spectroscopy and X-ray diffraction, we could conclude that the spherical onions have defective structures rather than the perfect fullerene structure. They possess dangling bonds and localized electronic states. On the other hand, the polyhedral onions are more graphitic and contain de-localized πelectrons.2) Thin films of carbon nanocapsules containing magnetic metallic particles : By means of co-sputtering and post-annealing, we could prepare thin films of carbon nanocapsules containing Ni, and NiCo alloy nanocrystals. By adjusting the alloy composition, the optimum magnetic characteristics could be achieved.3) Carbon onions as a candidate of interstellar dust : We measured the UV-Visible extinction spectra for carbon onions prepared from nanodiamonds and dispersed in pure water. Measured spectra could successfully be reproduced by theoretical calculations, which assume the aggregation of defective onions dispersed in water. Extending the calculation to an isolated spherical onion placed in vacuum, we could obtain an extinction spectrum that agrees very well with a measured interstellar extinction spectrum. This good agreement strongly suggests that the defective onions are one of the components of the interstellar dust.