Raman spectra of nickel-carbon nanocomposites

Abstract

ABSTRACT By using the solid-phase pyrolysis of phthalocyanines the nickel–carbon nanocomposites have been synthesized. The composition, structure, and morphology of samples were investigated by scanning electron microscopy and Raman spectroscopy. The first-order Raman shifts of prepared materials were measured with laser excitation at 514.5 nm in the frequency range from 900 to 2000 cm -1 . It is shown that the degree of graphitization in nanocomposites essentially depends on the pyrolysis temperature. By analyzing the intensity ratio of Raman D- and G-bands the mean sizes of graphitic nanocrystallites in prepared samples were estimated. Key words: solid-phase pyrolysis, nickel, carbon, nanocomposites, SEM, Raman spectra 1. INTRODUCTION In resent years, metal–carbon nanocomposites have attracted great interest both from the fundamental point of view and for many applications. In particular, they can be used in medicine, biology, as catalysts, sensors, magnetic paints, green materials, for gas storage, in lithium-ion batteries, etc. In our previous works [1,2] it was shown that the method of solid-phase pyrolysis of phthalocyanines is efficient for preparation of nickel–carbon nanocomposites with a sufficiently narrow distribution of sizes of Ni nanoparticles. It is essential that by changing the pyrolysis conditions one can fabricate ferromagnetic Ni nanoparticles of different sizes (from 10 to 500 nm) in different carbon structures: in amorphous carbon, carbon nanotubes, graphitic capsules, and carbon fibers. In particular, with increasing pyrolysis temperature, due to nickel–carbon catalytic interaction, the graphitization of carbon structures take s place, which was studied by scanning el ectron microscopy an d X-ray diffraction technique. Another efficient method for investigation of structure of materials is Raman spectroscopy. In particular, it is well-known that it is very useful in studies of carbon and gr aphitized structures (see, e.g., [3-16]). There is many works on Raman spectra of carbon thin films (including metal-doped films), however, only a few number of works is known related to bulk metal–carbon nanocomposites. The goal of this work was to investigate structural features of nickel–carbon nanocomposites with use of Raman spectroscopy.