學位論文
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Item 鐵超薄薄膜在銥(111)上之表面結構與磁學性質研究(2014) 陳暐翔; Wei-Hsiang ChenMagnetic properties and surface structure of ultrathin Fe/Ir(111) films have been investigated using the surface magneto-optic Kerr effect and low-energy electron diffraction. Layer-by-layer growth of Fe/Ir(111) is observed for the first three monolayers at room temperature. For Fe thinner than three monolayers, pseudomorphic growth of Fe films is observed. The layer distance is close to that of fcc(111) Fe. For Fe thicker than three monolayers, the surface structure can be identified to be related to the bcc(110) arrangement of Fe atoms in Kurdjumov-Sachs orientation. As the Fe thickness increases, the linear increase of the Kerr intensity is observed. The Kerr intensity comes from the bcc-Fe and a thin magnetic dead layer is observed at the interface. The magnetic properties and surface structure of ultrathin Fe/Ir(111) films after high temperature annealing treatment have also been investigated. The Fe atoms diffuse into the Ir(111) substrate to be a FexIr1-x alloy as annealing temperature increases. For annealing temperature between 750 K and 800 K, there is a blocking of the interdiffusion behavior for Fe atoms into the Ir(111) substrate and the existence of the specific concentration of Fe of the FexIr1-x interface alloy which shows a stable state at this annealing temperature region. Combining the experimental results of Auger analysis, LEED patterns and the theoretical calculations, one can conclude that the specific concentration of Fe of the FexIr1-x interface alloy at the stable state is Fe0.5Ir0.5 as annealing temperature between 750 K and 800 K. For 5~9 ML Fe/Ir(111) films, a layered structure of Fe/FexIr1-x/Ir(111) could be obtained after high temperature annealing treatment. The surface of this layered structure becomes flatter after the high temperature annealing treatment. The structure of the top Fe films can be identified to be related to the bcc(110) arrangement of Fe atoms in Kurdjumov-Sachs orientation, however, strained by the underneath Fe0.5Ir0.5 interface alloy since this interface alloy is also strained by Ir(111) substrate which leads to the change of the lattice parameter of the unit cell of Fe bcc(110) at the surface from 0.248 nm to 0.272 nm. The surface structure transition between the KS orientation to strained KS orientation for 5~9 ML Fe/Ir(111) at annealing temperature from 300 K to 700 K have also been investigated. For annealing temperature less than 550 K, the KS orientation shows low periodicity. The periodicity of this KS orientation gets better as annealing temperature increases and become stable as annealing temperature larger than 700 K. Finally, the structural, compositional and magnetic phase diagram of Fe/Ir(111) is constructed. For Fe film thinner than 3 ML at annealing temperature between 300 K and 900 K, no Kerr intensity is observed due to the fcc arrangement of Fe films and FexIr1-x alloy. For Fe films thicker than 3 ML, Kerr intensity could be observed owing to the bcc arrangement of Fe films. The coercivity and saturation magnetization enhanced abruptly (higher than Fe/Pt(111) system) after the high temperature annealing treatment which is because of the compositional and structural change of this system.Item 超薄氧化鈷膜在銥(111)表面上的製備與物性探討(2008) 李佳憲本論文內容將探討Co/CoO/Ir(111)超薄膜的薄膜成長與組成、表面磁性以及薄膜表面結構變化，並利用歐傑電子能譜儀、深度組成分析、表面磁光柯爾效應、低能量電子繞射等方法進行上述的研究。從薄膜成長與深度組成分析得知，在一定層數下的CoO會形成良好的化合狀態；將薄膜進行熱退火步驟後，O與Co的歐傑電子訊號比值會下降。CoO/Ir(111)超薄膜表面鍍上Co後，形成Co/CoO介面，零場冷卻後利用表面磁光柯爾效應儀測量磁滯曲線，發現隨著溫度的降低，矯頑力有增加的趨勢，但磁滯曲線呈現對稱的情況；在場冷卻下的表面磁性分析中，發現除了矯頑力增加，並且有交換偏移現象發生；從薄膜表面結構的觀察中，顯示出其結構週期性變強。經由系列化研究超薄膜系統在不同膜厚下的行為，可以得到鐵磁層與反鐵磁層間交換耦合的最佳條件。