H：Si(100)-3x1 to 2x1 表面結構相變化的觀察

Abstract

長久以來對於人們對於對於氫氣在矽表面的吸附反應已經有很多研究，但是對於氫脫附的動力學機制一直不是很瞭解；同時對於H：Si(100)-3×1 至 2×1 之間的相變機制一直存在疑惑。本論文研究利用H：Si(100)-3×1 至 2×1的相變化觀察中試圖去解決一些問題。實驗方法是利用化學氣象沉積方式吸附氫氣在Si樣品上，並讓樣品保持在400 K以形成H：Si(100)-3×1 結構後，加熱樣品到583 K以形成H：Si(100)- 2×1 結構，之後再利用掃描穿隧顯微鏡 ( STM ) 觀察樣品變化。實驗結果顯示H：Si(100)-3×1 在583 K時，會慢慢變成 2×1結構。在相變的初期裡，表面上H：Si(100)- 1×1區域會先直接造成氫原子結合脫附而產生2×1區域，在原本的H：Si(100)-3×1區域則會產生兩種相變機制，一種是兩個氫原子直接從一個H：Si(100)-3×1單位中結合脫附造成兩列 dimer ，且之後會往 dimer row 方向擴散。另一種是會造成H：Si(100)-2×1區域的聚集，而有σ鍵偏移一個晶格位子的現象，之後也是會延著 dimer 擴張H：Si(100)-2×1區域。

同時我們發現在相變過程中，H：Si(100)- 1×1區域會產生單原子缺陷( single vacancy；SV )與雙原子缺陷( double vacancies；DV )。本實驗對於氫氣的脫附與Si原子的再鍵結提出一些解釋，此外在形成H：Si(100)-2×1 的過程中原子的重新排列生長擴張以及錯位現象提供證據與解釋。

The adsorption of atomic hydrogen on the Si(100) surfaces has been widely studied for many years, but the detailed desorption mechanism remains a mystery. The mechanism of the structure transition from H：Si(100)-3×1 to 2×1 phase is also not yet clear. This work investigated dynamics and kinetics of H：Si(100)-3×1 to 2×1 phase transition. The H：Si(100)-2×1 surfaces were exposed to atomic H at sample temperature of 600 K and 400 K to obtain the H：Si(100)-2×1 and H：Si(100)-3×1 surface structure, respectively. Then, we heated the H：Si(100)-3×1 sample to 583 K and applied scanning tunneling microscopy (STM) to observe the surface morphology. The conversion of H：Si(100)-3×1 to 2×1 could occur slowly at the temperature and H：Si(100)-1×1 to 2×1 could be converted directly. Two H atoms must desorb in order to convert a sequence of dihydride-monohydride-dihydride(DMD) to a sequence of monohydride-monohydride(MM). The fact that σ-bond shift was found in this pathway. During the conversion of H：Si(100)-3×1 to 2×1, etching vacancies had always been found in H：Si(100)-1×1 domain. There were two kinds of vacancies, labeled SV (single vacancy) and DV (double vacancies). This thesis proposed the mechanism of desorption and H：Si(100)-3×1 to 2×1 rearrangement.