利用掃瞄穿隧顯微鏡觀察Si(100)-2´1:Cl表面上缺陷的移動及反應。

Abstract

本論文研究Si(100)-2´1:Cl表面上的缺陷在樣品溫度300 ~ 750 K間的移動和反應現象。實驗方法是利用掃瞄穿隧顯微鏡(STM)連續觀察樣品上缺陷的變化。實驗結果顯示，在室溫時，樣品上主要的缺陷是單原子缺陷(single vacancy；SV)和雙原子缺陷(dimer vacancy；DV)，缺陷在樣品溫度650 K以下不會移動。當樣品溫度大於650 K，單原子缺陷會沿著dimer row跳動，也會在雙原子單體(dimer)內跳動，雙原子缺陷則會沿著dimer row跳動。我們觀察到有三種不同的雙原子缺陷，它們的外觀及在高溫下的行為都不同。第一種雙原子缺陷會沿著dimer row跳動，第二種雙原子缺陷會分裂成兩個單原子缺陷，第三種雙原子缺陷則不會移動。在樣品溫度650 K 時，我們亦觀察到兩個單原子缺陷相互靠近，但並沒有形成穩定的雙原子缺陷。分析在不同溫度下(300-750 K)各種缺陷的面積，顯示在樣品溫度300-650 K間，各種缺陷面積總和增加了~30%，由此推論有微量的矽從樣品表面脫附。然而樣品溫度在650-750 K間，各種缺陷面積的總和並沒有增加(~5×10-2 ML)，而n-DV(n>2)的面積增加了2.7×10-2 ML，但2-DV和SV的總面積卻減少了2.9×10-2 ML，這些結果顯示樣品溫度在650-750 K時，2-DV和SV會結合形成n-DV(n>2)。

We have observed in real-time the thermal motions and reactions of various kinds of vacancies on Cl-saturated Si(100)-2x1 surface in the temperature range between 300 and 750 K using variable-temperature scanning tunneling microscopy. The motions of various vacancies were not observed below 650 K. At the temperature higher than 650 K, various events, including both intra-dimer and intra-row hopping of single vacancies, intra-row hopping of dimer vacancies and some rare events, occur. DV strings (n-DV, n>1) are not mobile over this temperature range (300-750 K). We also found that there are three kinds of DVs, labeled Type I, II and III, respectively. Their appearances and behaviors are quite different. Type I DVs hop along the dimer rows. The activation energy Ea and the prefactor of Type I DVs hopping along the dimer row is estimated to be around 1.44 eV and 4.6×108 s-1, respectively. Type II DVs are immobile, however can split into two SVs. Type III DVs also do not move at all time. The amount of total missing silicon atoms increased by ~30 % in the temperature ranging from 300 to 650 K. Between 650 and 750 K, the total missing silicon atoms remained approximately the same (~5×10-2 ML). Whereas the amount of n-DVs (n>2) increased by 2.7×10-2 ML (from 0.7×10-2 to 3.4×10-2 ML) and the amount of both 2-DVs and SVs decreased by 1.9 ×10-2 ML (from 2.3×10-2 to 0.4×10-2) and 1.0 ×10-2 ML (from 1.8×10-2 to 0.8×10-2), respectively. These results suggest that the increase of n-DVs (n>2) may due to the recombination of 2-DV and SVs at 650 – 750 K.