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

The ablation of a carbon target immersed in deionized water, in absence and in presence of ultrasonic waves is reported, and the differences investigated. The obtained nanostructures are characterized by transmission electron microscopy, Raman spectroscopy and photoluminescence. Transmission electron images reveal that the produced carbon nanostructures, with and without ultrasonic excitation, are graphene-like sheets with improved quality in the first case. Samples prepared with ultrasounds show graphene layers with large sizes (several microns) and regular shapes, whereas the samples prepared without ultrasounds show smaller sizes and irregular shapes; additionally, some dispersed quasi-spherical nanoparticles are observed in the samples prepared without ultrasound. Photoluminescence measurements of the obtained nanostructures reveal emission in the blue spectral region.