Abstract
The metal nanoparticles are interesting from the point of view of their optical properties, which strongly depend on both the particle size and shape. Surface plasmon resonances in metallic nanoparticles are used for a variety of applications due to the large enhancement and localization of the electromagnetic field at the metal/dielectric interface. The plasmonic coupling of metal nanoparticles with light enhances a broad range of useful optical phenomena, such as resonant light scattering, surface plasmon resonance absorption, metal induced fluorescence enhancement and surface-enhanced Raman scattering, all of which have tremendous potential for ultrasensitive chemical and biomolecular detection and analysis. Further functionalization of metal nanoparticles can be achieved by either laser exposure or surfactant. Moreover, the surfactant increases the stability of the nanoparticles and avoids the agglomeration and sedimentation. Surface functionalization of MNPs can be monitored in real time by UV-visible spectroscopy of the plasmon resonance. The optical and catalytic properties of Ag and Au nanoparticles are useful to a diverse range of applications. By combining these two metals into a single entity or forming core-shell structures, both the stability and catalytic properties can be further enhanced and localized surface plasmon absorption can be varied. In this talk, we present recent progress in laser ablation of noble metal target in a confining liquid for the synthesis of nanocrystals and formation of nanocomposites. In the recent years laser ablation synthesis in solution has emerged as a reliable alternative to traditional chemical reduction methods for synthesis of noble metal nanoparticles (MNP). The size manipulation by laser irradiation and functionalization of MNPs will be discussed. While femtosecond laser pulses can induce a shape transformation, such as a rod-to-sphere transition, nanosecond laser pulses can cause fragmentation into smaller particles. High fluences can be powerful enough to raise the temperature of the metal above its melting point, and thereby it can be used as a convenient tool to control the shape and size distribution of nanoparticles and intermediate phase nano-soldered composites. Also, the biofunctionality of laser-ablated gold nanoparticles can be tailored through the bonding between gold and amino-group. This linkage of amino-group to gold give rise to red shift in plasmon absorption band and related to the degree oxidation of gold. Nanoaggregate structures formed by gold nanospheres of different sizes and generated by laser ablation from solid gold into water will be discussed for their potential as enhancing nanostructures in surface enhanced Raman scattering (SERS).
