利用反射式高能電子繞射儀分析電沉積在鉑(111)電極上的鈷/鎳薄膜晶體結構

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题名:	利用反射式高能電子繞射儀分析電沉積在鉑(111)電極上的鈷/鎳薄膜晶體結構
作者:	蔡昇峰;Tsai,Sheng-Feng
贡献者:	化學學系
关键词:	高能電子繞射儀;掃描穿隧式電子顯微鏡;金屬薄膜;鈷;鎳;RHEED;STM;Cobalt;Nickel
日期:	2012-11-08
上传时间:	2012-12-25 13:34:56 (UTC+8)
出版者:	國立中央大學
摘要:	本研究以電化學方法沉積鈷/鎳金屬在鉑(111)電極上後，再將鉑(111)電極轉移進行RHEED繞射實驗，對照本實驗室先前in-situ STM圖像的研究結果，綜合討論出鈷/鎳薄膜的薄膜成長方式以及薄膜的晶體結構。在低覆蓋度1~2層鈷膜的情況時，鈷原子會以(111)面的排列方式吸附在鉑(111)面上，而且鈷(111)面中的原子成長方向為[-110]方向角，這與載體鉑(111)面的[-110]方向角相同，而電沉積上鈷原子傾向以自身的晶體結構(FCC,aCo=3.544Å)排列在鉑(111)電極之上，因外，我們還可以從RHEED圖中觀察到氧化鈷，而氧化鈷中鈷原子的間距為3Å，這與過去文獻氧化鈷單晶的鈷原子距離(3.01 Å)相符合，而氧化鈷中的鈷原子[-110]原子成長方向與載體鉑(111)電極相同；隨著鈷膜覆蓋度的增加，2~3層的鈷膜即可以在鉑(111)電極表面上觀察到twin結構的鈷金屬，而高覆蓋度鈷膜的三維晶格繞射點，可以在倒空間可排列出一個BCC的結構，而轉換成物理空間則為FCC晶體結構；這證明了鈷金屬沉積在鉑(111)電極表面時，鈷膜不傾向以自然界鈷金屬最穩定的HCP晶格結構排列，而是傾向以鈷(111)面FCC晶體結構成長在鉑(111)電極表面上。Ultrathin films of cobalt were electrodeposited onto a well-ordered Pt(111) electrode and were transferred into ultrahigh vacuum chamber to be characterized by reflection high-energy electron diffraction (RHEED) techniques. The morphology of these Co thin films was also investigated by in-situ STM. At a sub-monolayer coverage both pseudomorphic cobalt and bulk-like Co(111) adlayers are formed on the bare Pt(111) surface. The former tends to align itself with its [110] axis in parallel to the Pt[110] direction. The first Co (111) layer grows with the in-plane lattice constant of bulk Co and the close-packed atomic rows are aligned with its [110] axis in the Pt[110] direction. In addition, two cobalt oxide domains rotated by 30o with respect to each other are identified with an estimated interatomic spacing of 3 ?, which agrees well with that (3.01 ?) of the crystalline (111) plane of CoO whose [110] directions are aligned in the Pt[110] direction. Co twin nuclei were detected at 2-3 ML Co layers on Pt(111) by RHEED for the first time, and the deduced bcc reciprocal lattice with the fcc-related twin spots of bulk Co strongly provides evidence that Co grows with a fcc (111) rather than a hcp (0001) orientation on Pt(111).
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