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 (SEAS) and scanning electron microscopy (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 mu 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.