矽氧極化奈米結構非線性光學特性之研究

Abstract

在本論文中我們利用非線性光學技術探討新型材料『二氧化矽孔洞陣列嵌入矽奈米晶體』 的鐵電特性。我們估計材料的有效二階非線性係數為 deff =3.7 pm/V，並發現材料在波長480 nm 附近有強烈的共振現象。此材料的SFG訊號是來自於二極化項 (dipole)，確定樣品為具有鐵電性質的材料。改變材料溫度，我們發現其合頻訊號隨溫度增加，合頻訊號遞減，到達623K時，合頻訊號強度降為零。也就是說，材料的鐵電性質完全消失。由此實驗，我們用理論擬合出本材料之居里溫度為567K，此外樣品回溫過程中其鐵電性質亦具有恢復性。

A novel material of Si nanocrystals (Si-nc) embedded in a three-dimensional array of mesoporous silica matrix has been studied by nonlinear optical techniques. A resonance features around 480 nm were observed in the dipole induced sum frequency generation (SFG) from as grown samples. The effective second-order nonlinear coefficient is estimated to be deff =3.7 pm/V. The effect of optical SFG signals from this material by heating and cooling processes has also been investigated. The Curie temperature of the material was thus determined to be 567K. Our result confirms room-temperature ferroelectricity in Si-nc for the first time to our knowledge.