Coordination structure of implanted manganese ions in silica glass
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Coordination structure of implanted manganese ions in silica glass Kohei Fukumi, Akiyoshi Chayhara, Hiroyuki Kageyama, Kohei Kadono, Naoyuki Kitamura, Hirohsi Mizoguchi, Yuji Horino and Masaki Makihara Osaka National Research Institute, AIST, 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577 Japan ABSTRACT
180 keV Mn+ ions were implanted in silica glass at doses ranging from 1x1016 to 2x1017 ions/cm2 at room temperature. The coordination structure of implanted Mn atoms was studied by X-ray absorption spectroscopy. It was found that Mn atoms were mainly coordinated by O atoms in silica glasses as-implanted at doses lower than 5x1016Mn+ions/cm2. The Mn-O bond distance was 2.07 Å and the coordination number was 4.3 in average. Mn atoms were mainly coordinated by Mn and O atoms in the glasses as-implanted at doses higher than 1x1017 Mn+ions/cm2. In all the glasses, Mn atoms which are coordinated by O atoms were present as divalent state. After heating at 700 °C in air, Mn atoms were present as trivalent state and tended to form oxide crystals.
INTRODUCTION
Implanted ions are dispersed in silica glass at low local concentration, irrespective of thermodynamic stability [1,2,3], because the mass transport process is the rate determining step [4,5]. The coordination structure of implanted ions has, however, not been studied well. It is interesting to study the coordination structure of implanted ions which are not in the thermodynamically stable state. The coordination structure of implanted Mn ions has been studied by electron spin resonance spectroscopy [6] and x-ray photoelectron spectroscopy [7]. These studies have shown that there are divalent manganese ions in silica glass. The coordination number and bond length has not been studied yet, although they are important factors to determine properties of ion-implanted materials. In the present study, the coordination structure of implanted Mn ions has been studied by x-ray absorption spectroscopy, which is known as a powerful method to study the coordination structure of dilute ions. EXPERIMENT Mn+ ions were implanted in synthetic silica glass plates (Yamaguchi Nippon Silica Glass Co. Ltd, Direct method, OH content=1000 ppm) at an acceleration energy of 180 keV, an ion current of 6.3 µA/cm2 and doses ranging from 1x1016 ions/cm2 to 2x1017 ions/cm2. The projected range and straggling range of ions were 150 nm and 45 nm, respectively, according to TRIM code calculation. Each glass plate implanted at each dose was cut into several pieces, which were used for the following heat-treatment and measurement. The glass plates were heat-treated at 700 oC and 900 oC for 30 min in air. X-ray absorption spectra at energies around the Mn K-edge were measured at a BL7C beamline of Photon Factory, the National Laboratory for High Energy Physics. X-ray absorption spectra of the glasses were measured by a fluorescence mode with a O3.1.1
Lytle detector equipped with a Cr filter. Measurements for the glasses were repeated three times. X-ray absorption spectra of reference substances such
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