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 超薄鐵銥合金的成分比例與結構研究(2011) 李亞倫; Ya-Lun Li本論文主要研究鐵超薄膜在銥(111)基底上的成長模式、表面結構、化學偏移及合金成分比例。樣品製備與實驗均在超高真空環境下進行，並透過低能量電子繞射與歐傑電子能譜進行實驗觀測。在室溫300 K鐵超薄膜的成長方面，我們首先以歐傑電子能譜觀察一系列不同厚度之鐵薄膜，發現鐵薄膜在銥單晶上的化學偏移與塊材電負度所預期的結果有相反的趨勢。當鐵薄膜厚度超過2 ML時，其L1M1M2歐傑電子動能隨厚度增加而下降，銥N1N2N7歐傑電子動能隨厚度增加而上升，介面效應仍然明顯；厚度超過4 ML時，鐵L1M1M2歐傑電子動能變化趨於平緩，介面效應減弱，此時樣品的化學狀態以塊材鐵為主。從室溫300 K鐵超薄膜成長之低能量電子繞射實驗結果發現，當鐵薄膜厚度超過5.8 ML時，鐵原子主要是以bcc(110)在fcc(111)上的Kurdjumov-Sachs (KS)模式進行磊晶；當厚度小於1.8 ML時，鐵原子則以基底fcc(111)的方式進行磊晶。鐵超薄膜樣品加熱退火至800 K時，我們從歐傑電子能譜的強度分析可以得到穩定的鐵銥成分比例為1:3；化學偏移的分析發現銥N1N2N7歐傑電子動能比起乾淨銥單晶有下降的趨勢，因此排除鐵原子退吸附的可能；在低能量電子繞射實驗結果中，電子入射動能120 eV時可以發現清楚的(2×2)亮點。由以上三個實驗結果我們推測鐵銥形成規則合金FeIr3，最後透過氬離子濺射實驗進行深度分析，發現實驗所得之濺射效率與FeIr3模型的計算結果相差3%，顯示鐵銥確實形成規則合金FeIr3。另一方面，在低能量電子繞射實驗結果中，電子入射動能75 eV時，可以發現鐵銥合金表面上存在有鐵的兩種結構：bcc(110) KS與bcc(111) (3/2×3/2)R20°。當鐵超薄膜樣品厚度大於5.8 ML時，此兩種結構會同時存在於加熱退火後的FeIr3合金表面；當厚度小於1.8 ML時，合金表面將只剩下bcc(111)結構。Item 鈷在鉑上形成超尖磁性奈米針尖之研究(2009) 江佳倫; Chia-lun, Chiang我們利用場離子顯微鏡在超高真空的環境中觀察兩種磁性奈米針尖的成長，一種是利用表面皺化機制形成的鈷鉑合金金字塔形奈米針尖；另一種是藉由鈷在鉑(111)面的S. K. mode長成以鉑為基底的鈷奈米針尖。前者針尖生長於皺化形成的鈷鉑合金多面體之稜線交接處，分別位於{531}及{210}切面，{531}切面的金字塔是由擴張的{111}、{110}、{311}切面堆積，{210}切面的金字塔則由擴張的{110}及兩個{311}切面組成。而後者針尖是在室溫及20K時鍍鈷4～5ML於鉑(111)面，鈷原子先依鉑基底以FCC結構排列，再於其上堆積單顆、雙顆或三顆原子團，這些在鉑(111)面成長的鈷原子團即是一種無特定針形的奈米針尖。Item 透過氫氣作用控制磁性層間交互耦合效應(2017) 陳宜樺; Chen, Yi-Hua長期以來，鈀一直作為氫氣解離和吸附的高效催化劑。在鈀合金或內米結構中，鈀的氫化容易引起相鄰材料有顯著的鄰近效應。在本實驗中，我們在超高真空中使用電子束蒸發磊晶法，在MgO (001)的基底上製備了磁性界面耦合系統。通過退火處理，可以得到平坦的MgO (001)表面，用來沉積Fe/Pd/Fe三層膜。 在一定鈀的厚度下，通過磁光柯爾效應在平行(In-Plane)方向，可以在Fe/Pd/Fe/MgO(001)系統中觀察到清楚的雙磁滯曲線。這現象說明頂層和底層鐵層之間的反鐵磁耦合。隨著室溫下的氫氣脫吸附，反鐵磁層間耦合有明顯的變化，如雙磁滯曲線的矯頑場變化所示。這結果表示，鐵/鈀多層膜系統未來可以應用為敏感性高的氫氣感測GMR傳感器