Modification of nanofibrous carbon morphology under effect of laser ablation

Abstract

This paper presents the results of studies of carbon nanostructures obtained by the laser ablation of a nanofibrous carbon formed in the process of a catalytic decomposition of hydrocarbons in the presence of high-percentage catalysts containing the iron subgroup of metals. A continuous CO2 laser with a radiation density of 3.4 W/cm2 was used in the experiments. The target was placed on a cooled copper substrate in a helium medium under a pressure of 770–780 torr. Upon the impact of laser radiation, the carbon evaporated and, further, condensed on the surface of a special condenser. The samples were collected from the condenser surface and the target in the radiation-exposed area. The products were studied by high resolution transmission electron microscopy using a JEM-2010 electron microscope. A number of samples underwent a local energy dispersion X-ray microanalysis on the EDAX spectrometer. Multilayer nanotubes of diameters 14–40 nm and lengths of up to 2 μm have been found in the evaporated and condensed carbon materials. It was established that part of the nanotubes was filled by the catalyst metal. Interestingly, in the target area exposed to the radiation, the initial material comprising carbon nanofibers with the structure of inserted cones transformed into carbon nanotubes (CNTs) with an average cross-section size of 20 nm.