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.