以飛秒脈衝雷射製備La0.7Ca0.3MnO3薄膜及其超快動力學行為之研究

Abstract

在本論文中，我們分別利用飛秒脈衝雷射，以及奈米秒脈衝雷射，以脈衝雷射濺鍍法濺鍍La0.7Ca0.3MnO3薄膜，並且藉由La0.7Ca0.3MnO3薄膜基本特性的量測，以及超快激發探測系統(optical pump-probe spectroscopy, OPOP)，比較用飛秒脈衝雷射濺鍍La0.7Ca0.3MnO3薄膜，和用奈米秒脈衝雷射濺鍍La0.7Ca0.3MnO3薄膜，兩者之間的基本特性，以及超快動力學行為的差異。在超快激發檢測光譜當中，瞬時反射率的變化率ΔR/R，可觀察到弛緩時間在次皮秒至數個皮秒的快弛緩行為，以及弛緩時間在數十到數百個皮秒的慢遲緩行為。其中，慢弛緩行為所對應的物理機制為自旋¬-晶格(spin-lattice)的弛緩行為；而快弛緩行為，根據本實驗室之前的研究發現，對應的是極化子(polaron)的行為，也因此快弛緩行為的變化趨勢，與電阻率的變化趨勢相符合。在此論文中，我們會針對快弛緩行為做一系列的討論，以進一步確認快弛緩行為與極化子行為的關聯性。

In this work, we have explored a method to prepared La0.7Ca0.3MnO3 thin film by using ultrafast-pulsed laser of 5000 Hz. We have prepared La0.7Ca0.3MnO3 thin film via two different methods: one is nanosecond-pulsed laser deposition, the other one is ultrafast-pulsed laser deposition. We compare the two resultant samples to see what factors differs the consequence. We also use optical pump-probe system(OPOP) to measure the ultrafast dynamics of the two samples produced through nanosecond-pulsed laser deposition and ultrafast-pulsed laser deposition. We deliberately discuss the two sample’s fast component behavior and slow component behavior, which respectively corresponds to polaron and spin-lattice thermalization, to see what difference exists in the La0.7Ca0.3MnO3 thin film prepared via ultrafast-pulsed laser deposition, and investigate what might cause the difference. In the end, we conclude our work with some way we can use to improve ultrafast-pulsed laser deposition.