原子運動の電子加速とビスムスの乱れ
Germán Sciaini1, Maher Harb, Sergei G Kruglik
1Institute for Optical Sciences and Departments of Chemistry and Physics, University of Toronto, 80 St George Street, Toronto, Ontario M5S 3H6, Canada.
Nature
|March 6, 2009
まとめ
超高速電子 difrractionは,ビスムスのレーザー誘発溶解が190フェムト秒以内に発生することを明らかにします. この急速な固体から液体への相変化は,格子に沿った原子運動の電子加速によって引き起こされる.
科学分野:
- 凝縮物質物理学 凝縮物質物理学
- マテリアルサイエンス 材料科学
- 超高速スペクトル顕微鏡
背景:
- 超高解像度X線と電子 difraktionにより,固体におけるレーザーによる構造変化の原子レベルマッピングが可能になります.
- アルミニウムと半導体に関する以前の研究では,材料の性質と刺激に基づいて,異なる融解機構 (熱対非熱) が示されています.
- ビスムートのようなピエルス歪み系はユニークな格子ダイナミクスを示しているが,そのレーザー誘発の融解反応は未調査のままである.
研究 の 目的:
- フェムト秒電子 difraktion を使用してレーザー誘発溶解中の結晶ビスムスの構造的ダイナミクスを調査する.
- 強烈な光学刺激下でのビスムスの相変化の時間スケールとメカニズムを決定する.
- ビスムートの融解力学に対する興奮強度の影響を調査する.
主な方法:
- フェムト秒電子 difrractionは,結晶ビスムスの構造的変化を調査するために使用されました.
- 溶融を誘発するために,異なる激光刺激の強度を使用した.
- 原子構成と格子ダイナミクスは,フェムト秒解像度で分析されました.
主要な成果:
- ビスムスのレーザー誘発による融解は,高興奮強度で190フェムト秒以内に発生することが観察されました.
- 融解のダイナミクスは,刺激の強度に強く依存していることが判明しました.
- 融解は,不動のA(1g) 格子モードの半期間以内に発生し,例外的に速い移行を示しています.
結論:
- ビスムートの急速な溶解は,レーザーによって誘発されたグリッドの潜在エネルギー表面の修正に起因する.
- 原子が縦格子方向に沿って強く加速し,不安定な横断モードと結合することで,迅速な相変化が容易になります.
- ビスムスの原子運動は電子的に加速され,サブ振動時間スケールで固体から液体への相転換が可能になります.
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