Laser-controlled precipitation of gold nanoparticles in silicate glasses
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We report on the observation of space-selective precipitation of gold nanoparticles in Au2O-doped silicate glass by a method of irradiation with an 800-nm femtosecond laser and further heat treatment. The irradiated region of the glass first became gray in color after irradiation with the femtosecond laser and then turned red after further heat treatment at around 520 °C, indicating that gold nanoparticles have precipitated in the irradiated region of the glass. A possible mechanism has been suggested that the Au+ ions in the region irradiated are reduced to Au0 atoms by the femtosecond laser, and then the Au0 atoms accumulate to form gold nanoparticles with the glass sample heat treated. The observed phenomenon should have potential applications in the fabrication of ultrafast all-optical switches.
I. INTRODUCTION
Gold nanoparticles, used for more than 300 years in the coloration of glass to obtain so-called gold ruby glass,1 have again aroused the interests of scientists because of their unique optical properties,2–4 such as nonlinear optical properties and ultrafast nonlinear response, which are different from those of bulk gold as well as those of individual gold atoms or ions. Materials doped with gold nanoparticles have a large optical absorption coefficient due to the surface plasmon resonance of gold nanoparticles in wavelengths from 500 to 560 nm, and consequently strong enhancement of the third-order nonlinear optical susceptibility ((3)) has been observed around the peak of the absorption band. Glasses, with the advantages of being transparent and able to be made in bulk materials, have been used as base materials to dope gold nanoparticles. Extensive studies have been made on the fabrication of the glass doped with gold nanoparticles.5,6 Conventional methods used to obtain glasses containing gold nanoparticles fabricate Au+-doped glasses through traditional melting or ionexchange techniques, combined with heat treatment or ionizing radiation of the glasses to precipitate gold nanoparticles. Other techniques, such as sol-gel, chemical vapor deposition, sputtering, and ion implantation,7–10 are also widely used in the fabrication of the glass doped with gold nanoparticles. However, it is not easy to spaceselectively control the precipitation of gold nanoparticles in glasses by using these methods. Recently, we first used a new method combining the irradiation of a femtosecond laser and successive heat treatment to produce silver nanoparticles and succeeded in the space-selective J. Mater. Res., Vol. 18, No. 9, Sep 2003
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precipitation of silver nanoparticles inside glass.11 Nice butterflies, yellow in color, composed of silver nanoparticles, were drawn inside the glass sample. In the end of the paper of Ref. 11, it is mentioned that gold nanoparticles can also be induced to space-selectively precipitate inside glass, but no details were provided. In this paper, we report in detail on the space-selective precipitation of gold nanoparticles in Au+ dope
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