鈀和銥原子團在鎢(110)面上成長初期結構變化之研究

王雅慧

指導教授 ： 傅祖怡

國立臺灣師範大學/理學院/物理學系在職進修碩士班/碩士(2002年)

摘要

摘要
我們使用場離子顯微鏡直接觀察到鈀和銥原子團在鎢(110)面上成長時的各種結構變化，同時也討論了這些結構間發生變化的條件以及銥原子團在鎢(110)面上的擴散運動。鈀和銥原子團的成長最初期穩定結構是沿基底原子最密堆積的方向排列；接著鈀原子團在原子個數8顆以上時會轉變成以二維原子島為穩定結構，銥原子團在足夠的原子鏈密度及650K以上加熱溫度時也會形成穩定的二維結構。二維鈀和銥原子島的原子是按照基底排列為bcc(110)的假晶結構。當二維的鈀原子島成長至鎢(110)面的邊界後，會開始往三維方向成長，此三維原子島結構中的第二層鈀吸附原子排列，開始轉變成fcc(111)晶面上的原子排列方式。銥原子團則在二維原子島的成長就觀察到不易擴大的現象，有三維原子島的結構出現，但並非很穩定的狀況。1~7顆銥原子團在鎢(110)面上的擴散在原子個數5顆以下，和原子個數5顆以上的銥原子鏈有不同的擴散機制，我們以自由能討論了此不同之擴散機制，推論5~7顆銥原子鏈可能如鈀原子鏈一般發生原子一顆顆脫開的方式進行擴散；而3、4顆銥原子鏈則是發生整體的運動擴散。然而，是否仍有造成不同的擴散機制的其他因素，還需要更進一步的研究。

關鍵字

場離子顯微鏡 ； 結構轉變 ； 鈀 ； 銥 ； 鎢(110)

並列摘要

Abstract
The arrangements and structural transformations of Pd and Ir clusters on W(110) were observed directly by field ion microscope . When the transformations occur and how the Ir clusters diffuse on W(110) were also discussed .At the initial stage , the most stable structures of Pd and Ir clusters are linear chains which are parallel to the nearest-neighbor stacking directions of the substrate . For Pd linear chains beyond a length of about 8 atoms ,the preferred structure is a 2-D island configuration ; the linear Ir chains are more stable than Pd chains . The greater coverage and higher temperature(＞650K) are necessary conditions for transform to 2-D island . Both of Pd and Ir 2-D islands are pseudomorphic structure . When the 2-D Pd island continue growing to the size of 2-D Pd island is as large as the substrate plane of the W(110), we could observe the 3-D structures occur .The arrangement style of the second layer of Pd adatoms transform to fcc(111) crystal . The size increasing for Ir 2-D islands is difficult . The stable structure of Ir 3-D islands was not observed . The diffusion mechanisms of Ir chains on W(110) surface with number of atoms above and below 5 are different . By analyzing the free energies of the intermediate state , the diffusion mechanisms are concluded to two types for Ir chains . For Ir chains with 5~7 atoms , the most possible mechanisms is that one atom of the cluster moves to the nearest-neighbor site by hopping and the other atoms then follow in sequence . For Ir cnains with 3 or 4 atoms diffuse with a whole unit .

並列關鍵字

chain ； FIM ； iridium ； palladium ； structural transformation ； tungsten ； two dimensional island