Electronic structure and optical properties of concentric-shell fullerenesfrom electron-energy-loss spectroscopy in transmission - art. no. 155415

We present momentum-dependent measurements of the loss function of bulk sam ples of concentric-shell fullerenes using electron-energy-loss spectroscopy in transmission. It is shown that the pi and pi+sigma plasmons of these so -called carbon onions exhibit a significant momentum dependence, with a dis persion coefficient of about two-thirds of that of the corresponding plasmo ns in graphite. The optical properties derived from a Kramers-Kronig analys is are reminiscent of those found for polycrystalline disordered graphite. Furthermore, we find no changes of the electronic properties by alternating the average diameter of these carbon nanoparticles between 4 and 8 nm. Con sequently, concentric-shell fullerenes can be regarded as spherical graphit ic nanoparticles, whose electronic structure and optical properties, down t o a particle size of at least 4 nm, are strongly governed by the band struc ture of graphite.