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研究生： 莊家翔
Chiashain Chuang
論文名稱： 製作反鐵磁性的氧化鈷在鈷/矽(111)超薄膜上之交換偏移作用研究
Investigations of exchange bias effect for fabricating antiferromagnetic ultra-thin CoO films on Co/Si(111)
指導教授： 姚永德
Yao, Yeong-Der
蔡志申
Tsay, Jyh-Shen
學位類別： 碩士
Master
系所名稱： 物理學系
Department of Physics
論文出版年： 2009
畢業學年度： 97
語文別： 英文
論文頁數： 67
中文關鍵詞： 交換偏移 、超薄膜 、鈷 、矽 、反鐵磁性的 、鐵磁性的 、表面磁光柯爾效應
英文關鍵詞： exchange bias, ultr-thin films, Co, Si, antiferromagnetic, ferromgangetic, SMOKE
論文種類： 學術論文
相關次數： 點閱：205  下載：0 
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    • 交換偏移作用在半導體上的想法已經被初步的完成。為了完成這個想法，鐵磁性的元素-鈷，被覆蓋於半導體中最具代表性的元素-矽晶面上。研究交換偏移作用在半導體上的第一步驟是製作反鐵磁性的超薄氧化鈷膜。在此文獻中，有三種方法被用在製作反鐵磁性的超薄氧化鈷膜。它們分別是「在常溫下以氧壓下鍍鈷的方式製作超薄反鐵磁氧化鈷膜於11 ML 鈷/矽(111)上」、「在常溫下曝氧於鈷/矽(111)上」和「在常溫下以氧壓下鍍鈷的方式製作超薄反鐵磁氧化鈷膜於已曝氧4000 L達飽和的11 ML 鈷/矽(111)上」。
    在第一個方法中，不論是縱向和垂直方向的磁光柯爾效應，其阻隔溫度和交換偏向場都不遵守有限尺寸效應。這實驗結果顯示超薄反鐵磁性的氧化鈷膜或超薄鐵磁性的鈷膜中，可能有某種形式的奈米結構。
    在第二個方法中，我們得到一個指數上升的方程式，藉由這個方程式我們可以預測鈷矽化合物(CoSi2)的混合層數。在5在15的鈷原子層中，從AES強度氧鈷比飽和的強度變化換轉成氧的吸附層數，我們可以用一個指數上升的方程式曲線來近似這些數據。這個方程式可寫成IO = (IO)0 {exp[(tCo-t0)/D]-1}，其中(IO)0 = 0.41是氧的吸附比；t0 = 2.16 ML是鈷矽化合物(CoSi2)的混合層數；D = 6.98 ML是氧的平均擴散深度。
    在最後的方法中，介於鐵磁層鈷與反鐵層氧化鈷介面的氧中，形成氧阻隔層，它會降低鐵磁層鈷與反鐵層氧化鈷的交換作用。另一方面此氧阻隔層也降低反鐵層氧化鈷的形成效率。
    吾人提出三項重要的建議，它們分別是「零場冷卻過程」、「交換偏移磁性相圖」和「研究超薄反鐵磁層氧化鈷的表面形貌」。未來這三項建議若被實驗執行時，這可使我們交換偏移作用在半導體上的初步研究提升為交換偏移作用在半導體上的研究基石。

    The primitive step has already carried out for the idea about exchange bias (EB) effect on semiconductor. Ferromagnetic (FM) element cobalt was used to be the overlayers on the technologically most representative semiconductor silicon surface for the purpose. The first step to study the EB effect on semiconductors is to fabricate the antiferromagnetic (AFM) ultra-thin CoO films. In this thesis, three methods were used to fabricate the AFM ultra-thin CoO films. There are “evaporation of Co in oxygen atmosphere at room temperature (RT) on 11 monolayer (ML) Co/Si(111)” method, “exposure oxygen for oxidation at RT on Co/Si(111)” method, and “evaporation of Co in oxygen atmosphere at RT on 4000 Langmuirs (L) O2/11 ML
    Co/Si(111)” method.
    In the first method, for both polar Mogneto-optic Kerr effect (P-MOKE) and longitudinal magneto-optic Kerr effect (L-MOKE) on y ML CoO/11 ML Co/Si(111), the blocking temperature (TB) and exchange bias field (HE) are not related to the finite size effect. The results indicate that the FM ultra-thin Co layer or AFM ultra-thin CoO
    layer might have certain kinds of nanostructures.
    In the second method, we have an exponential growth equation to predict the thickness of compound layer – CoSi2. Between 5 and 15 monolayer of Co, the evolution of the experimental AES data are consistence with the exponential growth equation, IO = (IO)0 {exp[(tCo-t0)/D]-1}, where (IO)0 = 0.41 is related to the adsorption ratio of oxygen; t0 = 2.16 ML corresponds to the thickness of compound layers; D =
    6.98 ML corresponds to the average diffusion length of oxygen into the surface.
    In the final method, the adsorbed oxygen between the interface of FM ultra-thin Co films and AFM ultra-thin CoO films formed an oxygen blocking layer to decrease the exchange coupling between the FM ultra-thin Co films and AFM ultra-thin CoO
    films. On the other hand, it also decrease the efficiency for forming AFM ultra-thin CoO.
    Three important opinions were suggested by the author. There are “zero field-cooling process”, “exchange bias phase diagram” and “study the surface morphology on AFM ultra-thin CoO films by scanning tunneling microscopy (STM)” for advancing the primitive step to become a concrete step for the idea about
    exchange bias coupling on semiconductor.

    Contents 1 Introduction…………………………………………………………1 2 Basic concepts………………………………………………………3 2.1 Growth of thin films……………………………………………3 2.2 Magnetic anisotropy……………………………………………6 2.3 Exchange bias coupling…………………………………………9 3 Experimental instruments and methods…………………………13 3.1 Muti-functional ultra-high vacuum (UHV)systems………15 3.2 Auger electron spectroscopy (AES)…………………………16 3.3 Low-energy electron diffraction (LEED)………………17 3.4 Reflection high energy electron diffraction (RHEED)..18 3.5 Surface magneto-optical Kerr effect (SMOKE) ……………19 4 Results……………………………………………………………22 4.1 y L O2/x ML Co/Si(111)………………………………………22 4.1.1 Surface composition for y L O2/x ML Co/Si(111)………22 4.1.2 Crystalline structure for y L O2/x ML Co/Si(111)……27 4.1.3 Exchange bias coupling for y L O2/x ML Co/Si(111)…35 4.2 y ML CoO/11 ML Co/Si(111)…………………………………39 4.2.1 Surface composition for y ML CoO/11 ML Co/Si(111)…39 4.2.2 Crystalline structure for y ML CoO/11 ML Co/Si(111)41 4.2.3Exchange bias coupling for y ML CoO/11 ML Co/Si(111)44 4.3 y ML CoO/4000 L O2/11 ML Co/Si(111)……………………46 4.3.1 Surface composition for y ML CoO/4000 L O2/11 ML Co/Si(111)……………………………47 4.3.2 Crystalline structure for y ML CoO/4000 L O2/11 ML Co/Si(111)………………………………………………49 4.3.3 Exchange bias for y ML CoO/4000 L O2/11 ML Co/Si(111)…54 5 Discussion…………………………………………………………58 5.1 Correspondence with the thickness of compound layer – CoSi2 from y L O2/x ML Co/Si(111)…………………………………58 5.2 The magnetic properties of exchange bias coupling in nanostructures from y ML CoO/11 ML Co/Si(111)……………61 5.3 Outlook…………………………………………………………64 6 Summary…………………………………………………………65 References……………………………………………………………67

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