Electrophysical Properties of Onion-Like Carbon

Abstract

The paper examines electrophysical properties of onion-like carbon (OLC) samples, where particles have the average size of 4-8 nm and are formed by 5-10 nested fullerene-like spheres connected by 1-3 common curved graphene shells into aggregates with a size of 50-300 nm. We measured the temperature dependence of electrical resistance from 4.2 to 300 K and dependence of magnetoresistance in magnetic fields up to 6 T at the temperature of 4.2 K. Temperature dependences of electrical resistance of samples can be described within the framework of the Mott law with variable hop length for the one-dimensional case or within the framework of the Efros-Shklovskii Coulomb gap. We observed the quadratically increasing positive magnetoresistance up to 6 T associated with compression of wave functions of conduction electrons. Negative magnetoresistance was observed in the range of magnetic fields up to 1-2 T in the case of some samples. This is due to the fact that magnetic field suppresses the contributions to magnetoresistance made by interference effects in the area of hopping conductivity. The measurements were used to estimate the localization radius that is comparable to the diameter of OLC particles (nano-onions).The prospects of new nanotechnologies are largely associated with the development of new materials based on carbon nanostructures (nanotubes, fullerenes, onion-like carbon, nano-graphene films). These carbon nano-objects possess extraordinary mechanical, electronic, emission, capillary, sorption and other properties compared to conventional carbon materials. Many applications in the field of coatings shielding electromagnetic radiation are available for carbon structures [1], composites with different carbon additives (graphites, soot, carbon fibers, carbon nanotubes [2][3][4][5][6], and carbon aerogels [7]). It was recently discovered that OLC and composite materials based thereon possess enhanced ability to absorb electromagnetic radiation in the wide range of wavelengths [8,9]. In order to understand the absorption processes, it is necessary to carefully examine electrophysical properties of such materials.The samples of onion-like carbon were synthesized by method of thermal annealing of different types of nanodiamonds at the temperature of 1800-2140 K in high vacuum [10]. One can divide the process of nano-diamond graphitization under these conditions into two stages. At the first stage, the least connected carbon atoms detach themselves from the surface of nano-diamond crystallites. This condition is met by carbon atoms located at the borders of diamond defects, as well as carbon atoms of the crystallographic plane (111). At the second stage, fullerene-like envelopes of OLC are formed from the graphene fragments. The process of graphitization starts from the surface of 1 A. V. Nikolaev

Heat-treated nano-structured shungite rocks and electrophysical properties associated

“…2b) formed by smoothly bent packets of carbon layers. Some were similar to onion-like or fullerene-like carbon spheres with promising electrophysical properties [5,6]. Additionally, similar C-hollow particles have been found in the untreated shungite rocks and the rocks subjected to heating resulted from contact metamorphism [7].…”