非平衡液相・固相ガス原子クラスターの構造・状態分析に関する研究

Abstract

結晶性材料に強制的に注入・析出された原子クラスタの原子レベルの構造を、米国アルゴンヌ国立研究所と共同で研究した。Alの電子顕微鏡試験片中にXe(+)を注入し、析出した微粒子を高分解能観察し、その形態を解析した。その結果Xe析出物は約4nm以下のFCC(面心立方)構造を持った微結晶であった。(011)結晶軸の方向から観察すると、AlとXeの両者の格子定数の違いに起因する2次元モアレが認められ、その間隔はほぼAl格子縞3本おきであった。高分解能観察結果は制限視野回折像と一致し、これに基づいて析出物の3次元モデルを構築した。8つの(111)面と6個の(100)面に囲まれた14面体を作り、これをAl結晶中に埋め込んで、マルチスライス法によるイメージシミュレーションを行うと、得られた結果は実験結果をよく説明した。さらに軸上照射からわずかに結晶軸を傾斜させた高分解能観察では、Alの格子縞が観察されずXeのみの格子縞が観察でき、析出物の正確な形状が3次元モデルと良く一致していることがわかった。

An atomic level structure of atomic cluster precipitated after ion implation in crystalline material was investigated in an joint study with National Argonne Laboratories, USA. The fine particle of Xe(+), which was precipitated after implantation in Al specimen, was observed by a high resolution electron microscope in order to analyze its morphology. As a result, it was shown that the Xe precipitate was crystallite smaller than 4 nm with FCC (Face Centered Cubic) structure. When observing it from (011) direction, two-dimensional moire fringes caused by the difference in lattice constant between Al and Xe was observed. They appeared approximately every three lines of Al lattice pattern. The result of high resolution microscopy agreed with selected-area electron diffraction pattern. Based on these observed results, the three dimensional model of precipitate was constructed. The image simulation using multislice method was performed on the following model. The tetradecahedron with eight (111) planes and six (100) planes was constructed and buried in aluminum crystal. The obtained results explained well the experimental results. In the high resolution observation in which the crystal axis was slanted from the irradiation axis, the lattice pattern of Xe could observed separately without that of Al. The exact shape of precipitate agreed well with the three dimensional model.