Structure transformation of palladium and iridum clusters on the W (110) surface at intial stage

• Main Author: 王雅慧
• Other Authors: 傅祖怡
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/45332875598718159147

碩士 === 國立臺灣師範大學 === 物理研究所 === 91 === 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 .