Topology and Electronic Structure of Onion-Like Carbon and Graphite/Diamond Nanocomposites
- PDF / 703,289 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 40 Downloads / 166 Views
Topology and Electronic Structure of Onion-Like Carbon and Graphite/Diamond Nanocomposites. Lyubov G. Bulusheva1, Alexander V. Okotrub1, Vladimir L. Kuznetsov2, Andrew L. Chuvilin2, Yuriy V. Butenko2, Malcolm I. Heggie3 1 Institute of Inorganic Chemistry SB RAS, Novosibirsk, RUSSIA. 2 Boreskov Institute of Catalysis SB RAS, Novosibirsk, RUSSIA. 3 School of Chemistry, Physics and Environmental Science, University of Sussex at Brighton, UK.
ABSTRACT
Annealing of nanodiamond at moderate temperature makes it possible to produce structures being intermediate in the carbon transformation from sp3- to sp2-state (graphite/diamond nanocomposites) and onion-like carbon (OLC). Electron microscopy shows such structures involve cage shells with spacing close to graphite. X-ray emission spectroscopy has been applied to examine the electronic structure of OLC and graphite/diamond nanocomposites. The CKα-spectra of OLC produced in the temperature range of 1600-1900 K were found to be markedly different from the spectrum of particles formed at 2140 K and characterized by better ordering of graphitic shells. The latter spectrum was shown to be very similar to the CKαspectrum of polycrystalline graphite, while the former ones exhibited a significant increase of high-energy maximum that might be caused by the holed defect structure of graphitic networks forming at the intermediate annealing temperatures. To interpret experimental spectra, the quantum-chemical semiempirical AM1 calculation of icosahedral C540 cage and that with holed defects was carried out. The lack of at least 22% atoms in an internal carbon cage was found to be essential to provide an increase of density of high-energy electronic states similar to that observed in the spectrum of OLC produced at 1900 K.
INTRODUCTION
Onion like carbon (OLC) is one of the nanostructured forms of carbon consisting of fullerene like shells enclosed each into another. It can be formed via two principally different approaches. First approach uses a condensation of carbon atoms or small clusters in gas phase during an electric arc discharge [1] or in metal matrix [2]. Another approach is based on the transformation of condensed carbon under high-energy treatment. So Ugarte has found the curling and closure of graphitic networks of carbon soot into OLC particles under electron beam irradiation [3]. Later we developed technique, which allows producing hundreds of grams OLC by heat treatment of nanodiamond (ND) [4]. Two different types of OLC carbon can be produced by these mentioned methods, one contains spherical shells another one consists of polygonized shells. The latter contains fullerene like spheres with twelve pentagons, which preferentially responsible for the formation of polygonized structure. It should be mentioned that V9.22.1
polygonized OLC is usually formed after heat treatment of carbon soot [5] or spherical OLC [4] at the temperature higher than 2000 K. To explain the sphericity of onions formed under electron beam irradiation of carbon [6] the structural models includ
Data Loading...
