Carbon-based nanostructures obtained in water by ultrashort laser pulses

An ultrashort (100 fs) Ti:Sapphire pulsed laser has been employed in order to produce nanostructures by pulsed ablation of a graphite target in water. Different (10-100- 1000 Hz) repetition rates have been used, and the features of material produced have been investigated by surface enhanced Raman spectroscopy (SERS) and scanning electron micro- scopy (SEM). SERS spectra show that a broad asymmetric band associated with diamond-like carbon (DLC) is observed when repetition rates of 10 or 100 Hz are used. On the contrary, ablated species produced with 1 kHz pulses present a narrow peak at 1333 cm -1 , the typical mode of diamond, which is, however, embedded in a DLC band centered at 1540 cm -1 . SEM images show the presence of dispersed octahedral-shaped structures having a size from 1 to 5 ?m, in the case of 10 or 100 Hz repetition rates, and agglomerates of particles having a dimension below 300 nm, when 1 kHz pulses are used.