在(100)鑭鍶鎵氧基板成長a軸釔鋇銅氧薄膜之特性研究

Abstract

本實驗是利用脈衝式雷射( Pulsed Laser Deposition )鍍膜方式，在鑭鍶鎵氧(LaSrGaO4，LSGO )拋光基板上成長(100)釔鋇銅氧薄膜(Y1Ba2Cu3O7-x ， YBCO ) ，我們使用X-ray θ-2θ繞射掃瞄與晶體轉動曲線來分析薄膜結晶結構，及利用f方位掃瞄來分析薄膜晶粒平面排列方向的有序度；我們將薄膜製成沿著b 軸及沿c軸的微橋，並利用四點量測法(R-T)做薄膜電性的量測；使用原子力顯微鏡(AFM)、掃描式電子顯微鏡(SEM)、掃描式穿隧電子顯微鏡(STM)來分析薄膜表面狀態；利用X光吸收光譜(XAS)量測(100)YBCO薄膜的電子結構，因薄膜成長方向固定的緣故，有些入射角度並無法直接探測，如YBCO(001)薄膜，即無法探測垂直c軸(亦即90° )的吸收光譜，只能探測平行ab平面的吸收光譜，在此情況之下，YBCO(100)薄膜即可提供絕佳的互補，因為同步輻射X光的偏振方向是固定的，所以我們提供兩塊樣品，如此即可探測到不同晶軸方向(即平行c軸及平行b軸方向)的X光吸收光譜，在經由計算得到平行a軸的X光吸收光譜；及利用飛秒級鎖模鈦-藍寶石雷射，配合激發探測系統及一套開放式冷卻系統，以不同極化方向的激發探測光研究在不同溫度下，(100)YBCO薄膜的超快光學反應，這些特性量測的結果顯示(100)YBCO薄膜具有顯著的各向異性性質。

a - axis oriented Y1Ba2Cu3O7 (YBCO) superconducting thin films grown on (100) LaSrGaO4 (LSGO) substrates was investigated systematically by pulsed laser deposition technique. It was found that, in order to obtain high degree of preferred orientation growth, the use of P1Ba2Cu3O7 (PBCO) heterotemplate layer in desiralble. The obtained YBCO thin films were examined by using X-ray diffraction (XRD) with rocking curve measurement to check for the crystallinity. The in-plane orientation of the films was investigated by Φ-scan. The rocking curve of (100) diffraction peak was about 0.33o-0.58o with the in-plane alignment is about 95.3%, indicating the good quality of the obtained films. The temperature properties of the films were measurement by the standard four - probe method, and the surface morphology of the films was examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM) and Scanning Tunneling Microscope (STM). Furthermore, the anisotropies of the electronic structure and quasiparticles relaxation dynamics of the (100)YBCO films with X-ray absorption spectroscopy (XAS) and femtosecond pump-probe technique.