以場離子顯微鏡研究鎢表面上鈀吸附原子間的交互作用

Abstract

在這個研究報告中，研究了在鎢(211)面及鎢(110)面上，鈀吸附原子間的交互作用。在鎢(211)面上的同一通道中，二個鈀原子易形成距離最小（2.74埃）的雙原子團且以此結構在通道中擴散，二者間的交互作用能與次靠近結構的交互作用能相差為-110.2meV，雙原子團的擴散活化能為Ed＝0.59±0.01eV。當二個原子間的距離越大，其交互作用呈現有吸引也有排斥的震盪現象。在鎢(110)面上，我們加以探討原子間多體的效應，選擇F3lin＝-80meV、F3tri＝F3bent＝-8meV，其他如四個原子以上彼此之間的多體交互作用，在探討多個吸附原子的自由能時，是很重要的。除此之外，我們也探討了鈀原子團在鎢(110)面上擴散的機制，在雙原子團的擴散中，轉向且質心位移分別為2.23埃及1.58埃的機率與平移（質心位移為2.74埃）的機率差不多，它們都是原子向最鄰近位置運動二步而成，這也可由鈀三原子團發生平移（質心位移為2.74埃）的機率比轉向（質心位移為0）的機率大，而得到輔證。鈀雙原子團在鎢(110)面上的擴散活化能為0.65±0.01eV，鈀三原子團為0.68±0.01eV，當原子數目越多，擴散活化能越大，成單調增加，顯示鈀原子團的擴散皆為沿鄰近位置跳動組合而成，而無特別的交換機制。In this report, we study Pd adatom-adatom interactions on W(211) and W(110) surfaces. When two Pd adatoms are in the same channel of W(211) surfaces, they tend to be a dimer separated by 2.74angstrom and the dimer always diffuses along the channel. The interaction energy difference between a dimer and two adatoms separated by 5.48angstrom is –110.2meV. The diffusion activation energy of the dimer is 0.59±0.01eV. The interaction energy of two adatoms appears oscillation as the distance is increasing. A small Pd cluster on W(110) surfaces can form either a one-dimensional linear-chain structure or a two-dimensional island-like structure. From the probability of observing different structure on W(110) surfaces approach- ing thermal equilibrium, we discuss the importance of the many-body effect in the adatom-adatom interactions. In this study, we choose F3lin＝-80meV and F3tri＝F3bent＝-8meV. In addition, we measure diffusion parameters of small Pd clusters with 2 to 9 Pd adatoms on W(110) surfaces. From the probability of observing different atomic configurations of Pd dimers and Pd trimers, we discuss the possible cluster diffusion mechanisms. The diffusion activation energy of center of mass of Pd clusters increase with the number of atoms in cluster.