Study of the electronic structure and properties of 13C-isotope-based composites

The morphology and electronic structure of 13C-isotope-based graphite composites were studied by transmission electron microscopy (TEM), x-ray diffraction, and x-ray fluorescence spectroscopy. High-resolution TEM images showed that composites contain several forms of carbon particles. According to an x-ray diffraction analysis, the size of graphene stacks of graphite particles is 20 and 40 A. The CK α x-ray fluorescence spectra of the initial 13C isotope powder and composites based on it detected an increase in the density of high-energy occupied states in comparison with the graphite spectrum. Ab initio quantum chemical calculation of the structure of C150 graphene showed that the increase in the density of states stems from the electrons of dangling bonds of boundary carbon atoms of particles ∼20 A in size. Electrical properties of 13C-isotope-based samples were studied by analyzing the temperature dependence of the conductivity. It was assumed that the change in the logarithmic dependence of the conductivity observed at liquid-helium temperatures to the linear dependence as the temperature increases is caused by carrier transfers between the disordered graphene layers forming a nanocomposite.