Sizing gold nanoparticles obtained by laser ablation using Optical Extinction Spectroscopy

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

Québec City, Canada

Simposio; 9th International Symposium on Laser Precision Microfabrication (LPM 2008); 2008

Optical extinction for determining size distribution of gold nanoparticles fabricated by ultrashort pulsed laser ablation G. A. Torchia1,2,  L. B. Scaffardi1,3, C. Méndez2, P. Moreno2, J. O. Tocho1,4  and L. Roso2 1Centro de Investigaciones Ópticas (CIOp) Casilla de Correo 124 La Plata (1900), Argentina 2Servicio Láser Universidad de Salamanca Plaza de la Merced s/n 37008 Salamanca, Spain.3 Departamento de Ciencias Básicas, Facultad de Ingeniería, Universidad Nacional La Plata, Argentina 4 Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina gtorchia@usal.es; gustavot@ciop.unlp.edu.ar 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. It is well known that by means of femtosecond  laser ablation using moderated fluences (< 1000 J/cm2) a large number of small nanoparticles (<10 nm diameter) can be obtained by pure and clean fabrication method [1]. In this work we present 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. By using an improved theoretical model that modifies the contribution of the free electrons to the dielectric function introducing a size-dependent term, it is possible to fit the full experimental extinction spectrum considering a determined size distribution [2]. Figure 1: Solid line represents the optical extinction for gold Nps fabricated by fs laser ablation in deionized water.  Full circles correspond to the best fit including a size distribution of gold Nps of 1, 4 and 11 nm. Triangles and squares correspond to different bimodal distribution. Figure 1 shows the experimental data (solid line) and several theoretical curves made considering a distribution of several monomodal size particles. The best fit to the experimental data using a calculated curve which includes three Nps sizes: 1 nm (92%), 4 nm (7.8%) and 11 nm (0.2 %). Additionally, we also show results for two other bimodal distributions: 1 nm (92%) and 4 nm (8%) particles (triangles) and 4 nm (90%) and 11 nm (10%) (squares). The latter was included to show the influence of the addition of particles smaller (triangles) and larger (squares) than the average on the shape of the extinction spectrum.  In summary, we present an effective optical extinction method to determine a mix of several monomodal size distributions of gold Nps in water solution obtained by fs laser ablation with high fluence. We also show that optical extinction method is extremely sensitive for distinguishing slightly different size contributions for fitting the experimental spectra. [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.