Title : Production of colloidal Ag-Au alloy nanoparticles by nanosecond laser ablation and influence of DC electric field
The study of nanoparticles (NPs) have been interested within the past decades because of their applications such as nonlinear optics , nano-photonics , electrochemical , biological  and fiber sensors . NPs are remarkable due to their controllable electric, magnetic, optical and chemical properties. High surface to volume ratio and quantum size effects of nanostructures cause these properties. In general NPs are produced by chemical and physical methods. Chemical methods are more common and have the advantage of large scale synthesis of NPs, however toxicity, green incompatibility, and undesired radicals and products make these methods unsuitable in compare with physical methods .
Pulse laser ablation in liquids (PLAL) as a physical method has several advantages in compare with chemical methods. In PLAL a target is irradiated by laser pulse in a liquid environment. In this method, a portion of laser pulse energy is absorbed at the target surface and the target material heats up. In such condition the material may get melted, evaporated. Furthermore, when the beam intensity is high enough a plasma plume is formed on the target surface. The material is ablated by these mechanisms and NPs (and micro size particles) are formed in the environment liquid.
In this paper, synthesis of Ag-Au alloy nanoparticles (NPs) by laser post-irradiation is reported. Experimentally, in the first step colloidal of individual Ag and Au NPs were separately produced by nanosecond pulsed laser ablation in distilled water. In the second step an appropriate volume of these colloidal NPs samples was mixed and post-irradiated with the same pulsed laser beam. Finally, the post irradiation was performed in the presence of an external electric field (EEF).
The investigation was focused mainly on the size characteristics, optical properties and plasmonic properties of produced colloidal Ag-Au alloy NPs. The synthesized colloidal alloy NPs were characterized using the scanning electron microscopy (SEM) and UV-vis absorption spectroscopy. The results indicated that the EEF can reduce significantly the Ag-Au alloy formation time. The results also show that the wavelength of localize surface plasmon resonance of alloy NPs decreased by applied electric field.