Influence of Surfactants and Dissolved Gases on the Silver Nanoparticle Plasmon Resonance Absorption Spectra Formed by the Laser Ablation Processes

The silver nanoparticles were fabricated by the focused laser irradiation to silver rod immersed in various kinds of surfactant aqueous solutions. It was found that anionic and cationic surfactants showed different roles on the silver nanoparticle growth during the focused laser irradiation processes. Silver nanoparticle synthesis in an amphoteric surfactant aqueous solution was also carried out using the same techniques, and it was found that the spectral shifts for these surface plasmon bands showed complicated behaviors against the concentration of amphoteric surfactants as well as pH. Furthermore, the influence of the gas dissolved in a solution on the silver nanoparticle growth during the focused laser irradiation processes was investigated. With increasing the gas pressure of CO2, the surface plasmon bands of silver nanoparticles were shifted to longer wavelength, suggesting that the dissolved gas of CO2 in a solution enhances the silver nanoparticle growth. The plausible mechanism was proposed to understand the reason of such enhancement of silver nanoparticle growth by increasing the dissolved gas in a solution. 1. Introduction Nanoscale materials have attracted much attention due to their unique properties being different from their bulk materials [1]. For example, gold and silver nanoparticles have been used in various analytical techniques such as catalysis, biosensing, recording media, and photoscience. From the production point of view, chemical reduction of metal ions is mostly commonly employed in the preparation of metal nanoparticles in solution. In the last few years, a new methodology based on the laser ablation of bulk metal in water appeared for generating metal nanoparticles. The use of surfactants, especially, which covers the particles during their condensation, promotes improved size uniformity as well as reduces the coalescence during the fabrication of nanoparticles using such laser ablation techniques. Mafuné et al. [2] reported for the first time that the size distribution of silver nanoparticles produced by the laser ablation varied with the addition of sodium dodecyl sulfate (denoted by SDS hereafter) in water, and they also reported that the size became smaller and narrower with increasing the concentration of SDS. The authors also attempted the formation of stable platinum nanoparticles using the laser ablation of platinum plate in water and found that the particle diameter of platinum nanoparticles decreased with increasing the concentration of SDS [3]. Although the effects of the anionic surfactants of SDS on the size