脈衝雷射沉積法製備釔銩鐵石榴石薄膜的探討：結構、光學與磁性研究

Abstract

本論文以脈衝雷射蒸鍍法在c方向單晶藍寶石基板上製備100nm厚的TmxY3-xFe5O12薄膜，並探討薄膜鍍膜速率、薄膜的結構特性、光學性質及磁性的關係，其中單位面積雷射能量為3.5 J/cm2，鍍膜氧壓分別為3×10-1 mbar，Tm取代比例為x=0~3，基板溫度為750℃。 TmxY3-xFe5O12薄膜鍍膜速率不隨著取代比例增加而加快，鍍膜速率並無特定趨勢。X光繞射及拉曼散射光譜顯示隨著取代比例增加，薄膜由多晶轉為非晶結構，代表基板與薄膜的晶格失配度過大而無法形成單晶結構，薄膜在x=1.5時結晶品質最好。X光電子能譜分析，取得薄膜的銩與釔的實驗比例與理論值不符。利用原子力顯微鏡來看表面形貌與粗糙度，表面有許多柱狀晶體與粗糙度大約為20nm粗糙表面。超導量子干涉磁量儀測定與柯爾磁光顯微鏡結果顯示所有薄膜都沒有表現出磁性。

In this paper, a 100nm thick TmxY3-xFe5O12 film was prepared on a c-oriented single crystal sapphire substrate by pulsed-laser deposition. The relationship between the film coating rate, the structural properties, optical properties and magnetic properties of the film was investigated. The laser energy fluence is 3.5 J/cm2, the coating oxygen pressure was 3×10-1 mbar, the Tm substitution ratio was x=0~3, and the substrate temperature was 750 °C. The coating rate of TmxY3-xFe5O12 film does not increase with the increase of the substitution ratio, and there is no specific trend of coating rate. X-ray diffraction and Raman scattering spectroscopy show that the structure of thin films changes from polycrystalline to amorphous as Tm concerntration increases,and the film has the best crystal quality at x=1.5. According to the x-ray photoelectron spectroscopy, the experimental ratio of thulium to yttrium of the film is not in agreement with the theoretical value. The surface topography and roughness were observed by atomic force microscopy with a number of columnar crystals and a rough surface of approximately 20 nm roughness. The results of SQIUID and Kerr Magneto-Optical Microscopy showed that all films showed no magnetic properties.