研究生: |
蔡志申 |
---|---|
論文名稱: |
鈷超薄膜在鉑(111)表面之成長模式及和合金形成論文名稱 Growth Mode and ALloy Formation of Co Ultrathin Films on Pt(111) Surface |
指導教授: | 沈青嵩 |
學位類別: |
博士 Doctor |
系所名稱: |
物理學系 Department of Physics |
畢業學年度: | 85 |
語文別: | 中文 |
論文頁數: | 111 |
中文關鍵詞: | 鈷超薄膜 、鉑 |
論文種類: | 學術論文 |
相關次數: | 點閱:160 下載:1 |
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本論文的主題是以低能量電子繞射術、歐傑電子能譜術以及紫外光電子能譜術,研究鈷超薄膜在鉑(111)表面上的成長行為和合金形成;其內容包含起初的成長、交互擴散的動態研究、退火後的表面組成和結構相圖。在室溫及低溫下鈷超薄膜的成長呈現非同調性的磊晶,而在五個原子層的鍍量以上,低溫狀態下成長出的超薄膜其表面結構較粗糙;由交互擴散的動態研究可得到擴散活化能為0.9電子伏特,指數前擴散參數為6.6x10-11cm2/s;一個原子層的鈷超薄膜經過退火處理後,第一原子層和第二原子層各佔百分之五十的鈷原子;在此系統上,第一次發現兩個原子層的鈷超薄膜經過退火處理後,出現旋轉4.9度的區域;由低能量電子繞射術決定出的結構相圖展現出此系統多樣化的結構,有假性(1x1)、非同調性的磊晶、額外的p(2x2)、旋轉的非同調性的磊晶以及合金化的(1x1)結構。此外也研究銀超薄膜在鉑(111)表面上的成長行為和合金形成作為對比;銀在鉑(111)表面上的成長是依SK模式;一個原子層以內的銀超薄膜經過退火處理後,由於二維的銀鉑表面合金形成,會造成表面結構有異常的變化;一個原子層以上的銀超薄膜則不形成表面合金。
Low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and ultraviolet photoelectron spectroscopy (UPS) were used to study the growth behavior and the alloy formation of the cobalt ultrathin film on a Pt(111) surface. Initial growth, kinetics of inter-diffusion, surface composition after annealing and structural phase diagram have been represented in this thesis. Cobalt ultrathin film shows an incoherent epitaxy for depositing on Pt(111) at room and low temperatures. A rougher surface structure is observed for high coverages at low temperature. From the kinetic study of the inter-diffusion, activation energy and pre-exponential diffusion coefficient are obtained to be 0.90 eV and 6.6x10-11 cm2/s respectively. After annealing the one-monolayer Co ultrathin film on a Pt(111) surface at 600 K, both the topmost and the second layers contain 50 % of Co atoms. Rotated Co domains of rotation angle 4.9° with respect to the aligned substrate are observed for 2 monolayers of Co/Pt(111) af-ter annealing treatment. The structural phase diagram is obtained from LEED observation. Some structural phases of this system were observed: pseudo (1x1), incoherent epitaxy, extra p(2x2), rotational incoherent epitaxy, and alloying (1x1) structures. The changes in valence band structures during initial and phase transitions are studied by UPS. The Ag/Pt(111) ultrathin films are studied to compare with the Co/Pt(111) system. The growth of Ag/Pt(111) belongs to the Stranski-Krastanov (SK) mode. The surface structure has abnormal change between 550 K and 650 K in a submonolayer range because a disordered 2D Ag-Pt alloy is formed on the top layer.