利用飛秒雷射脈衝在BiFeO3(001)薄膜中產生與偵測同調聲頻聲子之研究

Abstract

若材料具有有序共存及強烈的鐵電-(反)鐵磁耦合，我們將此類材料稱為「多鐵材料」，多鐵材料展現豐富的物理性質，因此近年來吸引了科學家們爭先投入了磁電交互作用的尖端研究領域。在眾多的多鐵材料中，鉍鐵氧為室溫多鐵材料，其有高鐵電居里溫度與高尼爾溫度之特性，擁有製作成儲存元件之潛力。在本論文中，我們與朱英豪老師的團隊合作，委託他們提供我們良好的鉍鐵氧薄膜，透過超快激發-探測實驗，我們在ΔR/R訊號中發現一個週期為數十皮秒的振盪。此振盪的特性可透過由Thomsen 研究團隊所提出的「超快激發形變脈衝」理論模型來做解釋。最後，透過實驗結果我們推算出鉍鐵氧薄膜不同溫度時的聲速。

In recent years there has been an increasing interest in a new class of materials, in which both electrical and magnetic ordering can coexist. Such so-called multiferroic materials have many potential applications including a new type of memory device based on the combination of ferromagnetism and ferroelectricity. BiFeO3 is one such material and has attracted a wide attention. In the thesis, we cooperated with Y. H. Chu. They supplied BiFeO3 thin films to us. We have measured the transient reflectivity (ΔR/R) as a function of a pump probe delay at various temperatures. We found that a oscillation with a period of tens of tens of ps. The characterization of the oscillation can be elucidated by C. Thomsen [5]. Moreover, the sound velocity at various temperature has been calculated in the BiFeO3 thin films.