學位論文
Permanent URI for this collectionhttp://rportal.lib.ntnu.edu.tw/handle/20.500.12235/73905
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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 鋪覆超薄膜於針狀金屬表面之現象研究(2013) 陳晏清; Chen Yen Ching本實驗藉由場離子顯微鏡，觀察超薄膜鋪覆於針狀金屬表面之現象。其實驗現象可分為兩方向討論，其一為覆鉑於鈷針狀結構，由於切面擴張產生皺化現象。加熱退火至600K，可發現由於鉑之鋪覆，增加表面能異向性、降低皺化所需之加熱退火溫度，使得表面自由能較低的(0001)、(1013)、 (1013)切面擴張，並形成單條稜線，但由於鈷為非耐火性之材料，因此易受加熱退火影響，使得稜線成長不完整，難以觀察到金字塔堆疊。 另一方向為，覆矽於銥及鉑針狀結構，成長單層皺形之蜂巢結構-Silicene。由於場離子顯微鏡可看到同一樣品之各個切面，因此可觀察矽於各個切面成長之穩定結構：覆矽於銥(111)切面可發現，同時蒸鍍及加熱退火，可成長較特殊的結構；於銥(100)切面可觀察到矽原子排列成(3×2)之結構；於(311)、(310)及台階邊緣可成長帶狀、六角結構。 覆矽於鉑(111)切面，可觀察切面上可成長六角結構，與現在備受討論的議題-「Silicene」具有相似結構，因此推測鉑也可能成為成長Silicene之基底。Item 矽原子在銥(100)切面上的動態行為與交互作用(2016) 張琬喻; Chang, Wan-Yu本實驗利用場離子顯微鏡觀察吸附矽原子在銥(100)切面上的動態行為及交互作用。利用單顆吸附矽原子在不同溫度下的熱擴散運動，並配合Arrhenius plot求得擴散活化能E_d=0.91±0.02 eV。雙顆吸附矽原子在加熱到400 K以上時，彼此間的距離較低溫時的大，也間接證明在此溫度下，原子有足夠的能量去排列成有序結構。觀察雙顆吸附矽原子在銥(100)切面上的動態分布，顯示出矽原子在銥(100)切面上會位於不同佔位上(例如：四重對稱站位、橋位和上位)，也表示矽原子彼此間的交互作用力大於矽原子與基底間的交互作用。雙顆吸附矽原子會在相距三個銥基底的晶格常數下處在最低的交互作用能0.086 eV。原子間的交互作用會受到基底的二維自由電子氣影響，產生Fridel oscillation的現象，藉由理論公式與實驗數據擬合，可以得到銥(100)切面上的費米波向量應該為1.35 Å。當加熱到431 K時，蒸鍍在銥(100)切面下的矽原子會發生上行運動。