Fabrication of gold nanoparticles in intense optical field by femtosecond laser irradiation of aqueous solution
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Gold particles were fabricated by the high-intensity femtosecond laser irradiation of gold (III) chloride trihydrate (HAuCl4) aqueous solution. The structure and size distribution of the prepared particles were evaluated by transmission electron microscopy. The configuration of the gold particles varied with the concentration of the HAuCl4 aqueous solution. The mean particle size and size distribution were changed by the addition of polyvinylpyrrolidone (PVP), which acted as a dispersant, and monodispersed gold nanoparticles with a diameter of about 3 nm were successfully fabricated. The formation process of the nanoparticles is discussed in terms of the optical decomposition of molecules in the highly intense optical field generated by femtosecond laser irradiation.
I. INTRODUCTION
A femtosecond laser is able to produce an intense optical field of 1016 to 1018 W/cm2, which is close to the electric field inside a hydrogen molecule generated by the electrons. After the pioneering work on the Coulomb explosion by Cornaggia and co-workers,1–3 the photoionization and fragmentation induced by an intense laser field have been studied by numerical approaches.4–6 At the same time, experimental studies were carried out for many materials. The photoionization and fragmentation of inert gases, hydrocarbons, and organic gases were investigated mainly by time-of-flight (TOF) mass spectroscopy.7–11 Soft x-ray produced by higher-order harmonic generation7 intense enough to detect the Coulomb explosion were demonstrated,8 and the Coulomb explosion of benzene molecules were observed.9,10 However, these studies were mainly performed in an extremely low concentration of gas, for instance, at a pressure of 1.0 × 10−7 Torr for benzene.10 On the other hand, studies of intense laser irradiation of condensed matter such as liquid and solid have been also carried out. When an intense optical field of 1016 to 1018 W/cm2 is generated in the condensed matter, the resulting phenomena will be very complicated, and pure physical processes will be difficult to distinguish from other processes. Nevertheless, a lot of interesting phenomena under high-intensity optical field have been reported. For example, x-ray emission from water, CsCl and RbCl aqueous solutions,12,13 and the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0115 968
J. Mater. Res., Vol. 23, No. 4, Apr 2008
self-focusing and filamentation in liquid14,15 and solid16 media accompanying a chirped white light generation were also investigated. Accordingly, it is expected that such an intense optical field will strongly interact with molecules and produce highly charged ions resulting in significant optical decomposition of molecules and succeeding formation of different molecules or particles. Since this process is applicable to many types of molecule, the femtosecond laser irradiation of a liquid has the potential to be a novel method of material processing. In this work, we investigate the fabrication of gold particles by the
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