Phase Separation of Gold Microcrystals in Glass with an Electric Field
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Based on static electromagnetics theory and thermodynamics theory, a new model is proposed to describe the phase separation from the glass doped with metal particles in a static electric field. This model is proved by a heat-treatment experiment of boracic silicate glass doped with gold. The results indicate that the externally applied electric field promotes the phase separation of the glass and leads to a different size of the droplet phase just as this new model has predicted.
I. INTRODUCTION
II. THERMODYNAMICS MODEL
Composite glass doped with precious metal nanoparticles is a very attractive optical nonlinear material for optical switching and computing because of its ultrafast nonlinear response.1 In recent years, much effort has been made to develop it to satisfy the requirements of high speed and the ability to communicate a large amount of data. Among the precious metals, gold exhibits many good properties. Many preparation processes have been developed for it, such as melt-quenching and heat treatment,1,2 sputtering,3 ion implantation,4 sol-gel processing,5,6 and so on. The nucleation theory of the glass doped with precious metal is studied with the progress of the preparation processes.7,8 Melt-quenching and heat treatment in an electric field is a new preparation process. Previous research has shown the pronounced effect by an electric field on the kinetics of phase separation.9 In the investigations, a marked acceleration of phase separation in a complex silicate glass is noted for low-frequency fields of modest intensities. Recent research has shown that an electric field could promote or block the phase separation process due to the difference of the dielectric constant of the metal particle and the matrix glass.10–12 However, few investigations have been systematic. In this study, we proposed a new thermodynamics model to describe the phase separation of glass with an electric field and designed an experiment to prove it.
When a metal particle separates from the glass matrix, a solute-lean region poor in metal composition is formed around it, as shown in Fig. 1. As the dielectric constant changes along with the concentration of metal, the electric field in the glass will be altered. The electric energy change affects the thermodynamics process of the phase separation in the glass. Based on static electromagnetics theory and thermodynamic theory, the electric energy change in glass by the phase separation is calculated as follows.
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0133 1024
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 4, Apr 2004 Downloaded: 14 Mar 2015
A. Energy change of the electric field during phase separation
As we know when a nucleus forms, a solute-lean region poor in metal will form around it. The nuclei and the solute-lean regions are all approximately spherical. Because the metal concentration is usually very thin in the doped glass, the nuclei are sparse and the solute-lean regions are much
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