OPTICAL EXCTINTION TO DETERMINE A SIZE DISTRIBUTION OF GOLD NANOPARTICLES FABRICATED BY ULTRASHORT PULSED LASER ABLATION

G. A. TORCHIA; L. SCAFFARDI; P. MORENO; C. MÉNDEZ; L. ROSO; J. O.TOCHO

Tenerife, Spain

Conferencia; 9th International Conference on Laser Ablation (COLA 2007); 2007

Nowadays, the fabrication and manipulation of nanoparticles is a sounding topic in applied physics which is demanded from different research areas such as biology, medicine, photonic, etc. Traditionally, chemical methods are the main way to generate nanoparticles which require special laboratory conditions and are not environmentally clean. Also, in order to control shape, size and to avoid agglomeration of the generated nanoparticles, these kind of processes need to use chemical compounds such as stabilizer agents and surfactants, which are not suitable for biological applications or physics studies when pure nano-system are required. Laser ablation represents an alternative clean method which has been efficiently used during the last years to produce small metal particles with size control [1]. As it is expected, this method constitutes a simple and a safe way to preserve the environment and boostering the biological or medical applications. This work presents the advantages of optical extinction technique to fit gold nanoparticles size distribution corresponding to a colloidal solution fabricated by using femtosecond pulsed laser ablation within deionized water. The Au nanoparticles used in this work were obtained with a CPA Ti:Saphire (l = 796 nm) system which has a 120 fs pulse width, 1 KHz repetition rate and up to 1 mJ of output energy per pulse. It is well known that by means of fs laser ablation using moderated fluences (< 1000 J/cm2) a large number of small nanoparticles (<10 nm diameter) can be obtained [1]. By using an improved theoretical model that takes into account the size effect on the  contribution of free electrons to the dielectric function for Au nanoparticles [2], the experimental UV-visible extinction spectrum for a given size distribution could be reproduced. Complementary, in order to support the particles size distributions obtained, SAXS using synchrotron radiation and TEM spectroscopy were used. These results showed good agreement with the optical data and revealed that the predominant nanoparticles sizes were 4, 6 and 11 nm radius. Optical extinction measurement plus theoretical model presented in reference [2] represent an efficient, simple, low cost, fast and easy method to describe any broad size distribution for Au nanoparticles independent of the fabrication process. [1] A. V. Kabashin and M. Meunier, Synthesis of colloidal nanoparticles during femtosecond laser ablation of gold in water, J. Appl. Phys. 94 7941 (2003). [2] L.B. Scaffardi N. Pellegri , O. de Sanctis and J.O. Tocho, Sizing gold nanoparticles by optical extinction spectroscopy. Nanotechnology, vol.16, no.1, Jan. 2005, pp. 158-63.