Production and structural characterization of carbon soot with narrow UV absorption feature

In the present study, by a simple method, carbon soot with a narrow absorption features at around 220 nm was produced by pyrolysis of methane gas at a hot (1400-2800 °C) filament. A detailed correlation between the structure and the optical spectra of carbon soot was carried out using a high-resolution transmission electron microscope. It appears that the origin of the narrow absorption peak is an onion-like graphitic structure. Interestingly, we found that the absorption peak position and the size of the soot can be controlled by the production temperature. The absorption peak is located at 217.5 nm, i.e., at the position of an intense interstellar absorption, when the onion structure has about 5 nm diameter. Infrared spectroscopy was applied to further elucidate the chemical composition of the obtained soot.