Synthesis of core–shell copper–graphite submicronic particles and carbon nano-onions by spark discharges in liquid hydrocarbons

Spark discharge in hydrocarbon liquids is considered a promising method for the synthesis of various nanomaterials, including nanocomposites. In this study, copper–carbon particles were synthesized by generating spark discharges between two Cu electrodes immersed in heptane, cyclohexane, or toluene. The synthesized particles were characterized using scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. Overall, two families of particles were observed: Cu particles (diameter < 10 nm) embedded in a carbon matrix and submicrometric Cu particles encapsulated in a carbon shell. The obtained results indicate that the size distribution of the Cu nanoparticles and the degree of graphitization of the carbon matrix depend on the liquid. Indeed, discharges in heptane lead to Cu particles with diameters of 2–6 nm embedded in a carbon matrix of low graphitization degree, while discharges in toluene result in particles with diameters of 2–14 nm embedded in carbon matrix of high graphitization degree. Based on the obtained experimental results, it is proposed that the Cu nanoparticles are produced in the plasma core where Cu (evaporated from the electrode surface) and carbonaceous species (decomposition of the liquid) are present. When the plasma hits the electrode surface, hot (thousands of Kelvin) Cu particles are ejected from the electrode, and they propagate in the liquid. The propagation of the hot particles in the liquid results in the local evaporation of this liquid, which leads to the formation of a C-shell around each Cu particle. In few cases where the shape of the Cu particle is not spherical, carbon nanoonions are detected between the C-shell and the Cu core. These nanoonions are supposedly formed under the effect of the fluid vortices generated close to the particle surfaces when these latter are ejected into the liquid.

Двухстадийная конверсия кремния в наноструктурированный углерод методом согласованного замещения атомов

Abstract—A fundamentally new method of obtaining epitaxial layers of nanostructured carbon on silicon substrates has been considered. Epitaxial growth in the case of seemingly incompatible lattices has been achieved by converting the crystal by the method of coordinated substitution of atoms, in which the overall structure of the bonds between the atoms is not destroyed. In the first stage of conversion, the first half of the silicon atoms are concertedly replaced by the carbon atoms due to the reaction of silicon with CO gas, during which an epitaxial layer of SiC–3C cubic silicon carbide is obtained. In the second stage of conversion, the remaining half of silicon atoms is concertedly replaced by carbon atoms due to the reaction of SiC with CF_4 gas. Carbon structures with different properties from nanodiamonds to nanotubes and carbon nanoonions have been obtained depending on the orientation of the silicon surface, pressure of the reagent gas, and temperature and growth time. A key feature of this method is that the substrate orders the resulting structures using the original chemical bonds between the atoms in silicon. The term “concertedly” means that new chemical bonds are formed simultaneously and concertedly with the destruction of old bonds. Data on electron diffraction and analysis of Raman and ellipsometric spectra of the obtained samples of nanostructured carbon on silicon substrates have been presented. Two competing growth mechanisms have been discussed.