2-dimensional carbon nanostructures obtained by laser ablation in liquid: effect of an ultrasonic field

Abstract

The ablation of carbon targets immersed in deionized water, in absence and in presence of ultrasonic waves is reported, and the differences investigated. The lasers used were an excimer laser emitting 20 ns pulses at 193 nm and a Nd:YAG laser at 355 nm..The obtained nanostructures were characterized by Transmission Electron Microscopy (TEM) and Raman spectroscopy. Transmission electron images reveal that the produced carbon nanostructures obtained at 193 nm, with and without ultrasound, are graphene-like sheets. The samples prepared without ultrasound have larger sizes of several microns and more regular shapes whereas those prepared with ultrasound have sizes of less than a micrometer and irregular shapes; additionally, in this last case, some quasi-spherical particles with sizes around 10 nm are observed. Irradiating at 355 nm results in the production of small nanoparticles in both cases. Figure 1 a, and 1b, show the graphene-like structures obtained without and with ultrasound respectively. In figure 1c the crystalline character of the graphene-like structures is shown. Additionally, the targets were analyzed in the irradiated zone by Raman spectroscopy in both cases (with and without ultrasound). Some differences were found indicating local structural changes in the case of ultrasound presence.