兆赫輻射時析頻譜於釔鋇銅氧薄膜及基板之研究

Abstract

在本論文中，我們以兆赫輻射時析頻譜研究鑭鋁氧（LaAlO3）、氧化鎂（ＭgO）、釹鎵氧（NdGaO3）、鈦酸鍶（SrTiO3）四種基板及釔鋇銅氧（YBa2Cu3O7）薄膜在兆赫輻射波段之高頻介電性質及釔鋇銅氧薄膜之倫敦穿透深度等超導性質。 我們以自行架設之兆赫輻射源及電光取樣系統架設兆赫輻射時析穿透頻譜系統，此系統含有一低溫真空腔體及一除水氣設備，可進行樣品的變溫及低濕度量測；在樣品的製備上，我們以脈衝雷射蒸鍍技術製備在鑭鋁氧、氧化鎂及釹鎵氧三種不同基板上之釔鋇銅氧薄膜，並將鈦酸鍶基板以機械研磨的方式研磨至0.1mm；同時我們由電磁理論出發進行相關之理論推導計算及頻譜分析研究，並撰寫程式以完成其數學運算過程。 最後，我們可得樣品之複數透射係數比、複數折射率、複數介電常數、複數導電率等物理參數在兆赫輻射頻段下隨頻率及溫度變化之行為，並進行相關討論，而在釔鋇銅氧薄膜的研究上，我們可由二流體模型下的複數導電率求得其倫敦穿透深度之變溫行為。

In this thesis, we analyze the high frequency dielectric properties of LaAlO3、ＭgO、NdGaO3 and SrTiO3 substrates and YBa2Cu3O7 thin films in terahertz frequency with terahertz time domain spectroscopy and the superconductive properties of YBCO thin films such as London penetration depth. We setup the terahertz time domain spectroscopy system by the terahertz source and the electro-optic sampling system by ourself. This system which contains a cryostat and a dewater system, and the measurement can be work in different temperatures and low moisture. The YBCO thin films are deposited on LAO, MgO and NGO substrates by pulsed laser deposition, and we thin the STO substrates to 0.1mm by mechanical polishing. Meanwhile, we prove the equations from the electromagnetics and analyze the spectroscopy. We write the programs to complete the mathematic calculating procedure. Finally, we get the frequency and temperature dependent physical constants of samples, such as complex transmittance, complex index of refractions, complex dielectric constant, and complex conductivity, in terahertz radiation, and make discussions. In the YBCO thin films study, we can get the temperature dependent London penetration depth from the complex dielectric constant under the two-fluid model.