矽晶表面上氫和氯原子的換位運動觀察與熱力學研究

Abstract

利用掃描穿襚顯微鏡(STM)，本論文報導我們在Si(100)- (2×1):Cl樣品表面上氯和氯原子的換位運動觀察與其熱力學的探討。首先，我們觀察原本存在Si(100)-(2×1):Cl表面上的Cl位置”缺陷”並進一步觀察這種”缺陷”於樣品溫度570~650K之間的移動現象，我們發現這種缺陷有兩種動態，一種是沿著dimer row方向產生跳動稱為inter-dimer跳耀、另一種則是在同一個dimer內跳動稱為intra-dimer跳耀。接著我們曝上氫原子於Si(100)-(2×1):Cl表面。在570 K時，氫原子幾乎很少移動或久久移動一次，但當溫度增加到650K時，氫原子移動的速度較溫度在570K時快，並且在兩張影像間已有多次跳耀的現象發生。這些現象和移動的速度跟未曝氫原子於表面時所比較是相吻合的。由Arrhenius 關係線，我們推算出氫-氯原子交換運動的動力能障，即對於曝氫而言inter-dimer跳躍的動力能能障為1.23 eV、至於intra-dimer跳耀的動力能則為0.70 eV，相對的，在對於沒有曝氫的inter-dimer跳耀的動力能為1.14 eV，intra-dimer跳耀的動力能則是0.62eV。從此結果我們可以更加的確定在未曝氫的Si(100)-(2×1):Cl表面上產生移動的”缺陷”是樣品處理中殘留的氫原子或Cl2氣體中殘存的HCl分子吸附。

We have observed in real-time the motion and behavior of hydrogen atoms on Cl-saturated Si(100)-(2x1) surfaces with temperatures ranging from 570 to 650 K using ultra-high vacuum variable-temperature scanning tunneling microscopy (STM). We have taken STM movies with and without additional exposure of hydrogen atoms onto the Cl-terminated surface. The STM images show that there were two types of H-Cl exchange movement: inter-dimer and intra-dimer. By observing the H-exposed Cl sample we traced the movements of H sites. At 570K, hydrogen atoms seldom moved and their motions were mainly single jumps. As the temperature increases, the frequency of the movement becomes higher. At 650K, hydrogen atoms move at a fast pace and multiple jumps dominate in our sequential images. We obtained similar results from the non H-exposed Cl sample. By plotting the Arrhenius relations we were able to obtain the activation energies for each set. From the set with H-exposure we obtained 1.23eV for inter-dimer hoppings and 0.70eV for intra-dimer hoppings respectively, while for the set without H-exposure we obtained 1.14eV and 0.62eV for the inter-dimer and intra-dimer hoppings respectively. Therefore, we were able to confirm from these results that the vacancies we have seen moving on the non H-exposed Si(100) Cl-terminated surface as the residual hydrogen atoms got on the surface during sample preparation and/or from the HCl impurities in the Cl2 gas source.