X-ray Absorption Fine Structure Study on Coordination State of Implanted Gold Ions in Silica Glass
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X-ray absorption fine structure study on coordination state of implanted gold ions in silica glass Kohei Fukumi, Hiroyuki Kageyama, Kohei Kadono, Akiyoshi Chayahara, Nagao Kamijo, Masaki Makihara, Kanenaga Fujii, Junji Hayakawa, and Mamoru Satou Osaka National Research Institute, AIST, 1-8-31, Midorigaoka, Ikeda, Osaka, 563-8577 Japan (Received 11 September 1997; accepted 21 January 1998)
Coordination state of gold atoms implanted in silica glass to an energy of 1.5 MeV and a dose of 1 3 1017 ionsycm2 has been studied by x-ray absorption fine structure spectroscopy. It was found that most of the gold atoms form gold clusters in which ˚ than that in the nearest neighboring Au–Au interatomic distance is shorter by 0.05 A bulk gold. The contraction of Au–Au interatomic distance of gold clusters in silica glass is less than that reported in the previous studies on gold clusters within the other substrates. Gold atoms are coordinated by about four gold atoms in average. In addition, it was found that Au–O bonds are formed at the gold clusters/silica glass interface. It was deduced that the formation of Au–O bond at the gold clusters/silica glass interface depresses the contraction of Au–Au interatomic distance.
I. INTRODUCTION
Recently, much attention is being directed to glasses dispersed with ultrafine particles for their utilization to nonlinear optical materials.1 Since nonlinear optical properties of the glasses depend on the size of particles,2,3 it is significant to control the growth of the particles. Determination of the structure of ultrafine particles or clusters in glasses is of fundamental importance in the study of growth mechanism of particles. It is known that the structure of ultrafine particles and clusters is different from that in bulk substances. It has been shown that the mean-square displacement and the mean-square-relative displacement of atoms increase with a decrease in particle size.4,5 Moreover, it has been reported that a further decrease in particle size causes the contraction of interatomic distance and the decrease in average coordination number of atoms in particles. For example, the contraction of interatomic distance has been found in nickel and copper metal clusters on carbon substrate,7 copper clusters in solid argon,8 iron clusters in solid neon,9 gold metal clusters in Mylar films,5,6,10 and gold metal clusters prepared by the Schmid method.11 In contrast, it has been shown that platinum metal clusters prepared by an impregnation method on silica and alumina have an interatomic distance similar to ˚ although the coordination bulk platinum within 0.02 A, number in the former is smaller than that in the latter.12,13 This indicates that the contraction is depressed by the interaction between platinum metal clusters and oxide substrates. Previously, we have prepared silica glass dispersed with ultrafine gold particles by ion implantation and subsequent heat treatment, and have reported that the glass has high optical nonlinearity.14,15 Fu
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