臺灣博碩士論文加值系統

此篇論文分為兩大主題,第一部分是透過斜角度之方式鍍鐵於藍寶石基板(0001)上,最後覆蓋上鈀約30 ML,目的是保護基板上的鐵磁層避免氧化。所有的樣品皆在超高真空腔(UHV:10-9torr)之下用熱蒸鍍原理製程,隨後破真空於大氣下量測,包含磁光柯爾效應(MOKE)、X光繞射(XRD)、邊緣X射線吸收系微結構(EXAFS)、掃描穿隧式電子顯微鏡(STM) 等等。藉由改變鍍膜鐵的角度和鐵的厚度,可以控制鐵薄膜的磁性行為;當鍍膜的傾斜角度越大的時候,會使得表面粗糙度和原子排列的亂度越大。
第二部分是鈀吸附氫氣的實驗,於UHV系統下製備n ML Pd/Fe,接著用MOKE量測曝氫後的磁性行為。發現曝氫於一大氣壓後,會產生消光角的位移以及p方向電場平方(|E_p |^2)的改變。隨著鈀厚度的增加,消光角位移程度越大, |E_p |^2的變化量也越大,在特定檢偏鏡角度下,發現MOKE訊號會隨著Pd的厚度(30 ML~60ML) 而增加10%~40%。之後我們固定Pd的厚度在 60 ML,改變中間的鐵磁層,比較Pd/Fe、Pd/Co、Pd/Ni曝氫的行為,發現MOKE訊號的增加量分別增加約40%、35%、和60%。同時也量測吸附和脫附氫氣所需的時間以及飽和所需之氫氣壓力,三個樣品的氫氣飽和壓力都在100 mbar 以下,當氫氣壓力於1 atm 所需飽和時間皆小於10分鐘,但氫氣脫附的時間, Pd/Fe、Pd/Co 約需要8小時, Pd/Ni 只需不到2小時,而且其反應都是可逆的。
關鍵字:斜向鍍膜,磁光柯爾效應  

This study is separated into two parts:
(1) Using oblique deposition to change the surface morphology. (STM measurement) We investigated the corresponding magnetic behavior (MOKE measurement), and the crystalline structure (XRD, EXAFS measurement) in Pd/Fe/Al2O3(0001) system.
(2) H2 effect in MOKE, we absorption H2 from 10-3 mbar to 1013 mbar and measured MOKE in Pd/Fe,Co,Ni/Al2O3(0001) systems.

In many studies, surface morphology plays an important role in magnetic behavior. They are many methods to change it, like ion-sputtering, different stepped substrate…etc. One of the feasible methods is changing the surface morphology by different deposit angle.
In Pd/Fe/Al2O3(0001) system. In normal deposition, Fe atoms were follow the sapphire (0001) growth, and the corresponding magnetic hysteresis loop was almost square, it was isotropy. In oblique deposition, Fe grains were connected to form a 1-dimenstorn ripple structure, and habited interesting magnetic behavior. The easy axis is parallel to the ripples, and the hard axis is perpendicular to the ripples. In easy axis, the magnetic hysteresis loop was also square but the coercivity was much bigger than normal deposition. In hard axis, we could see the obvious uniaxial magnetic anisotropy.
Another ideal in this experiment was H2 absorption effect on MOKE. We capped Pd films on the top surface after Fe deposition. There are two reasons for the Pd capping layer, one is to protect Fe films oxidation, the other is Pd can adsorption H2 and the optical of MOKE is changed.

key words: oblique deposition, magnetic optical Kerr effect

Abstract……………………………………………………………………….1
1. Introduction
1.1 Uniaxial Magnetic Anisotropy in Pd/Fe/Al2O3 (0001) by oblique deposition. …………………………………………………………………...5
1.2 H2 absorption effect in room temperature by MOKE measurement in Pd/Fe,Co,Ni/Al2O3 (0001) system………………………………………….7
2. Basic Concepts
2.1 Magnetic material…………………….……………….…………………….8
2.2 Hysteresis loop………………………….…………………….…………….8
2.3 Kerr Rotation and Intensity……………………………………………….10
2.4 Shadowing effect by oblique deposition…………………………………11 2.5 Magnetic Anisotropy Energy (MAE)……………………………………...12 2.6 H2 absorption effect with Pd thin films……………………………………15
3. Experimental instrument
3.1 Ultra High Vacuum (UHV) system………………………………………..17 3.2 Low Energy Electron Diffraction (LEED)…………………………………20 3.3 Auger Electron Spectroscopy (AES)……………………………………..25 3.4 Magneto Optical Kerr Effect (MOKE)…………………………………….28 3.5 Scanning Tunneling Microscopy (STM)………………………………….33 3.6 X-Ray Diffraction (XRD)…………………………………………………...35 3.7 Extended X-ray Absorption Fine Structure (EXAFS)…………………...37
4. Experiment and Result (Part 1.)
Uniaxial Magnetic Anisotropy in Pd/Fe/Al2O3(0001) by oblique deposition.
4.1 Preparing Pd/Fe(0,45,65-deg)/Al2O3(0001)………………………………39
4.2 MOKE-magnetic behavior………………………………………………….40
4.3 XRD- crystalline structure……………………………………………….....44
4.4 EXAFS- crystalline structure……………………………………………….47
4.5 STM-morphology…………………………………………………………....49
4.6 MOKE-magnetic behavior in Pd/Fe(25ML)-0,45,65˚/Al2O3(0001) ……..51
4.7 Hc and Mr ration V.S. Azimuthal angle……………………………………53
4.8 Hc in easy axis V.S. Fe thickness, deposition angle 0, 45, 65˚…………55
4.9 Ku in Hard axis V.S. Fe thickness, deposition angle 45, 65˚……………57
5. Experiment and Result (Part 2.)
H2 absorption effect in room temperature by MOKE measurement in
Pd/Fe,Co,Ni/Al2O3(0001) system
5.1 Preparing Pd/Fe,Co,Ni/Al2O3(0001)……………………………………....60
5.2 To proofread the Precise Rotator………………………………………….60
5.3 How to measure Kerr rotation curve and correspond intensity…………61
5.4 n ML Pd/Fe/Al2O3(0001) + H2………………………………………………63
5.5 60 ML Pd/Fe,Co,Ni/Al2O3(0001) + H2………………………………….….70
6. Discussion and Questions….………………………………...74
7. Summary……………………………………………………………….…..77
8. Bibiography……………………………………………………………….79

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