Far-ultraviolet to near-infrared optical properties of carbon nanoparticles produced by pulsed-laser pyrolysis of hydrocarbons and their relation with structural variations

The optical properties of carbon black nanoparticles produced by infrared (pulsed-) laser pyrolysis (IRLP) of gaseous hydrocarbons and their relation with particle morphological and structural variations were studied. Different pulsed-IRLP samples were produced by changing the hydrocarbon precursor from chain-like (acetylene and ethylene) to aromatic (benzene) as well as by modifying the incident laser power and the photosensitiser/precursor ratio. The samples were characterised by infrared (IR) and near-infrared to far-ultraviolet (NIR/FUV) spectroscopy and by transmission electron microscopy (TEM). Typical parameters such as particle diameter, graphene layer size (La), energy gap (Eg), and π–π∗ band position were determined from the experiments and correlated to each other. The scattering contributions to the extinction were measured in the NIR/ultraviolet (UV) range for most of the samples, and in the FUV range for two of them. The use of benzene as precursor led to larger particles that also showed higher conductivity than those produced from acetylene or ethylene, with Eg values of the order of 0.8–1.5 eV depending on the experimental conditions. A slight decrease of the particle size with increasing laser power was also observed. Variations of particle size due to the precursor’s nature were found to be determinant in terms of the spectroscopic variations. Scattering losses appeared small in the case of the acetylene- and ethylene-based samples (up to 20% at 4 μm−1), whereas they increased in the case of the benzene-based samples (up to 56% at 4 μm−1). Laser power induced variations were found to be weak compared with the variations induced by the nature of the precursor.