Fabrication of gold and silver nanoparticles by femtosecond laser ablation. Size determination by optical extinction spectroscopy

D. C. SCHINCA; L. B. SCAFFARDI; G. A. TORCHIA; F. VIDELA; P. MORENO; L. ROSO

Kobe, Japan

Congreso; The 5th International Congress on Laser Advanced Materials Processing LAMP 2009; 2009

JLPS- Japan Laser Processing Society, Japan

Noble metal nanoparticles (Nps) were produced by femtosecond (fs) laser ablation of solid targets immersed in different liquid media. Different production conditions were explored to optimize fabrication of Nps with radii smaller than 10 nm.  Gold nanoparticle colloids in water were fabricated and subsequently fragmented in a two-step procedure, using the fundamental emission of a Ti: Sapphire fs laser (800 nm). Silver nanoparticles in water were fabricated and fragmented in a one-step procedure with the second harmonic of the same laser (400 nm).  For ethanol as surrounding medium, a combination of fundamental and second harmonic was used respectively to perform the two-step procedure.                 Plasmon peak position and its full width at half maximum (FWHM) was used to analyze the UV-visible extinction spectra of the different colloids obtained and to determine the size distribution of the produced Nps.  From this analysis, it can be concluded that radii under 20 nm were obtained for gold. In this case, the plasmon peak shows a blue shift after fragmentation, suggesting a noticeable reduction in radius under 10 nm. For silver, the plasmon resonance peak remains fixed around 400 nm after fragmentation, depending on media. However its FWHM is larger than that of the non fragmented sample, also suggesting a decrease in size.   There is a good agreement between extinction spectroscopy results and those from TEM analysis.  For gold, different mechanisms involved in the decrease of particle size due to fragmentation, together with the possible role of supercontinuum absorption are discussed.