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研究生: 張惟祐
Michael
論文名稱: 氧與氧化鈷在鈷/矽(111)超薄膜上之磁性研究
Investigations of magnetic properties for oxygen adsorption and ultra-thin CoO films on Co/Si(111)
指導教授: 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: 2008
畢業學年度: 96
語文別: 中文
論文頁數: 206
中文關鍵詞: 曝氧
英文關鍵詞: exchange bias
論文種類: 學術論文
相關次數: 點閱:153下載:0
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  • 摘要

    本實驗在超高真空的環境中,使用蒸鍍的方式將Co膜成長在Si (111)-7×7表面上,通入高純度之O2來研究曝氧效應對於Co/Si(111)超薄膜之影響,以歐傑電子能譜儀分析其表面成份,以低能量電子繞射儀以及反射式高能量電子繞射儀觀察其表面週期性結構,以表面磁光柯爾效應儀量測其磁性質。

    在純Si (111)基板以及CoSi2介面上,O2會有弱物理吸附而不形成化合態;在鍍上Co膜後,O2吸附之效應較強,且吸附效果隨著Co膜厚成正相關。而O2的吸附作用將改變Co/Si(111)超薄膜之表面磁性層的電子組態改變,故MS、MR與其磁滯曲線角型比皆呈現下降之趨勢。此外由於O2的吸附之效應,一方面降低了有效磁性Co的層數,因而降低了HC;另一方面形成了釘紮區域(pinning sites)阻礙磁化的反轉,因而提高HC,而本系統所觀測到HC之變化為此兩種效應互相競爭的結果。

    另一方面,以氧壓下鍍Co的方式製作超薄反鐵磁CoO膜於11 ML Co/Si (111)上,其易磁化軸由原本的水平膜面轉變至傾斜出膜面。且經過場冷卻至150 K可發現水平膜面與垂直膜面兩方向皆有交換偏壓的現象產生。於 CoO膜厚為20 ML時,此系統有最大水平膜面交換偏向場為258 Oe,且其阻隔溫度為200 K;而於CoO膜厚為15 ML時,此系統有最大垂直膜面交換偏向場為924 Oe,且其阻隔溫度為164 K。

    Abstract

    The purpose of this research is to study effect of oxygen exposure and ultrathin antiferromagnetic CoO films on the magnetic properties of ultrathin Co/Si(111)-7×7 surface. All experiments were in-situ performed in an ultrahigh vacuum (UHV) chamber with a base pressure of 2.5×10-10 torr, which was equipped with Auger electron spectroscopy (AES) for surface composition analysis, low-energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED) for surface structure analysis, and surface magneto-optic Kerr effect (SMOKE) for magnetic properties measurement.
    For Si (111)-7×7 surface and CoSi2 interface, it is found that oxygen is weakly adsorbed. As the thickness of Co films increases to above 5 monolayers (ML), pure cobalt islands start to accumulate on the surface and the amount of oxygen on the surface increases with increasing the oxygen exposure time. The adsorbed oxygen influences the electronic density of states of Co and leads to the decrease of saturated and remanent magnetization and poor squareness of demagnetization. The trend of coercivity with oxygen exposure is mainly governed by two competed factors: one is the reduction in the effective ferromagnetic Co films, resulting in the decrease of the coercivity; another is the action of oxygen as pinning sites to impede the magnetization reversal, leading to the enhancement of the coercivity.
    On other hand, the method to fabricate the antiferromagnetic CoO film is the evaporation of Co in oxygen atmosphere. As ultrathin CoO film is grown on 11 ML Co/Si(111) films, the direction of easy axis is transformed from in-plane to canted-out-of-plane. Interestingly, both longitudinal and perpendicular exchange bias phenomena are observed for 15 ML CoO/ 11 ML Co/Si(111) films measured at T = 150 K after cooling in a field H = 700 Oe from T = 300 K, and the maximum perpendicular exchange bias field of 924 Oe and the blocking temperature of 164 K are attained for 15 ML CoO, while the maximum longitudinal exchange bias field of 258 Oe and the blocking temperature of 200 K are obtained for 20 ML CoO.

    目錄 第一章 序論 10     1-1 前言 10     1-2 文獻回顧 12        1-2-1 交換偏壓 12        1-2-2 薄膜的交換偏壓 14     1-3 實驗動機與目的 16 第二章 基本理論 24     2-1 磁性物質 25        2-1-1 磁性物質的種類 25     2-2 磁異向性理論 31     2-3 交換磁異向性 38        2-3-1 理想鐵磁/反鐵磁介面模型 38        2-3-2 交換偏向場的理論模型 40     2-4 薄膜成長理論 43        2-4-1 成長過程 43        2-4-2 薄膜磊晶形式 45 2-5 表面物理 47 第三章 實驗儀器與工作原理 49     3-1 真空理論 50        3-1-1 真空定義 50        3-1-2 真空材料與封合 50        3-1-3 超高真空系統的設置 53     3-2 樣品的備置 68        3-2-1 Si單晶 68        3-2-2 試片座 68        3-2-3 樣品清潔 71     3-3 超薄膜蒸鍍系統 75     3-4 歐傑電子能譜儀 76        3-4-1 歐傑電子的產生機制原理 76        3-4-2 歐傑電子能譜儀的設置 82     3-5 表面磁光柯爾效應(SMOKE) 84        3-5-1 表面磁光柯爾效應原理 84        3-5-2 表面磁光柯爾效應儀之配置 88 3-5-3 調校柯爾訊號最大訊噪比之步驟 91     3-6 低能量電子繞射儀 93        3-6-1 低能量電子繞射儀之原理 93        3-6-2 低能量電子繞射裝置 97     3-7 反射式高能電子繞射儀(RHEED) 99        3-7-1 反射式高能電子繞射儀原理 99        3-7-2 反射式高能電子繞射儀之配置 101 第四章 實驗結果與討論 103 4-1 樣品表面分析與膜厚之計算 104 4-1-1 表面成分分析 104 4-1-2 膜厚計算 107 4-2 氧與氧化鈷在Co/Si(111) 超薄膜上之表面結構 108 4-2-1 乾淨的Si (111)-7×7 樣品表面結構 108 4-2-2 x ML Co / Si (111) 超薄膜的表面結構 110 4-2-3 氧在Co/Si (111) 超薄膜上之表面結構 113 4-2-4 氧化鈷在11 ML Co/Si (111)上之表面結構 116 4-3 曝氧效應對於x ML Co/Si (111)超薄膜表面成份之影響 119 4-3-1 曝氧於純Si (111) 基板上之表面分析 119 4-3-2 曝氧於CoSi2 上之表面分析 122 4-3-3 曝氧於 x= 5、8 ML Co/Si (111)之超薄膜表面分析 125 4-3-4 曝氧於x=11、13、15ML Co/Si (111)超薄膜表面分析 136 4-3-5 曝氧於x ML Co/Si (111)超薄膜表面成份綜合討論 149 4-3-6 5000 L O2/15 ML Co/Si(111)之深度分析 154 4-4 曝氧於x ML Co/Si (111)超薄膜之磁性研究 156 4-4-1曝氧於 x= 5、8 ML Co/Si (111)超薄膜之磁性研究 156 4-4-2曝氧於 x=11、13、15 ML Co/Si(111)超薄膜之磁性研究 163 4-4-3曝氧於x ML Co/Si(111)超薄膜之磁性影響綜合討論 172 4-5 x ML CoO/11 ML Co/Si (111) 超薄膜之研究 175 4-5-1 x ML CoO/11 ML Co/Si (111) 之表面分析 175 4-5-2 x ML CoO/11 ML Co/Si (111) 之磁性質 178 4-5-3 x ML CoO/11 ML Co/Si (111) 於不同溫度下之磁性質 182 4-5-4 x ML CoO/x ML Co/Si(111) 磁性質之綜合討論 189 第五章 結論 192 參考資料 196 附錄1. 以歐傑電子能譜儀 (AES) 觀測化學偏移 203 附錄2. Error Bar 205

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