鈀在鎢(211)表面一維通道上之長程交互作用

Abstract

在先前場離子顯微鏡的研究，發現兩顆鈀原子在鎢(211)表面，在相同通道以及相鄰通道上吸附原子的交互作用具有振盪的形式，即為Friedel Oscillation。FIM受到空間限制，只能看到局部的範圍，因此希望藉由掃瞄穿隧顯微鏡來觀察鈀原子在鎢(211)表面上，受到基底引發的交互作用影響，是否會形成特殊的表面結構。在我們的實驗中，利用離子濺射的方式來清潔樣品表面，接著曝氧氣搭配機械手臂上的加熱板和樣品座中的PBN加熱板加熱退火數次，可得到乾淨的基底表面。利用液態氮使得樣品降至低溫100K之後再蒸鍍鈀原子，觀察鈀吸附原子的分佈；由於在110K單顆的鈀原子會開始擴散，而鈀的雙原子團亦會在250左右發生擴散的行為，因此在我們的實驗中，讓樣品回溫至120K、200K以及RT，再降至低溫100K來觀察鈀吸附原子的分佈，並且統計在相同通道上不同吸附位置出現的次數，然後計算出鈀吸附原子之間的交互作用能。實驗結果發現在低溫或是回溫之後，都可以看到交互作用能有振盪的情況，表示即使回溫至室溫，基底引發的交互作用依舊存在；受到此交互作用的影響，在回溫至120K的實驗中發現鈀吸附原子會形成特殊的拉鍊結構。隨著回溫的溫度提高，也觀察到鈀原子聚集形成島的現象，而且島的數量有增加的趨勢，不過島的大小卻沒有明顯的增減。

Previous FIM studies showed that the interaction energy between two Pd adatoms on W (211) surface in the same and the nearest channels had oscillation form. It is called Friedel Oscillation. However、FIM was confined by space and it could only see a limited range. Therefore、a special surface structure could be observed by means of STM when Pd adatoms was on W (211) surface. In the present study、ion sputtering was used to clean the sample. The sample was annealed in an oxygen environment several times by two heaters simultaneously in order to obtain clean W (211) surface. After the sample was cooled down to 100K with liquid nitrogen、Pd adatoms was deposited and the distribution was observed. The single Pd atom would start to diffuse at 110K and so did the Pd dimmers at 250K. In the experiment、we raised the temperature of the sample to 120K、200K and RT and then cooled it down to 100K to observe and counted the times of different adsorption cites in the same channels. Next、we evaluated the interaction energies of Pd adatoms. It was found that whether at the low temperature or high temperatures、the interaction energies with the oscillatory behavior in different cases existed. Even if the temperature were raised to RT、the substrate mediated interaction continued to exist. In addition、Pd adatoms formed special zip structure at 120K due to the substrate mediated interaction. Finally、Pd adatoms were assembled to form islands with the rise in temperature. The numbers of islands increased but the size of islands almost remained the same.