F Hajiesmaeilbaigi - Laser & Optics Research School, NSTRI, P. O. Box ۱۱۳۶۵-۸۴۸۶, Tehran, Iran
A Motamedi
B. N. Mortazavi

Alloy nanoparticles have received special attention due to the possibility of tuning the optical and electronic (and thus catalytic) properties over a broad range by simply varying the alloy composition. It is well known that the surface plasmon bands are characteristic for the metal and alloy nanoparticles[1-4]. Plasmon modes in metals such as gold and silver fall in the visible spectral region. The position of the plasmon resonance maximum depends on the refractive index of environment and the size of the particles. As the particle size and its refractive index increase, the plasmon resonance shifts to the red [5]. Core-shell nanoparticles will give rise to two surface plasmon absorption bands and the individual band intensities should depend on the initial composition of the metal ions. A similar situation will arise from a dispersion containing separate gold and silver nanoparticles instead of the homogeneous alloy particles [3]. Absorption of laser radiation by metal nanoparticles is determined by the detuning of the laser wavelength from the plasmon resonance and the nanoparticle size. If the adsorb energy is sufficiently large the nanoparticle can melt. The nanoparticle in the liquid state can react with vapors of the surrounding liquid or other nanoparticles. The formation dynamics of alloy nanoparticles under laser radiation should strongly differ from the core-shell nanoparticles, because in the former case nanoparticles are not initially in contact. A core-shell structure could be readily prepared through a heteronucleation process and the metal with the faster reduction forms the core and the other is the surrounding shell. In this paper the synthesis of Ag/Au nano alloy by exposing the mixture of individual colloids to laser radiation was experimentally studied .