臺灣博碩士論文加值系統

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.

摘要………………………………………………i
Abstract……………………………………… ii
Acknowledgements……………………………iii
Contents………………………………………iv

Chapter 1 Introduction................ 1
1.1 Motivation......................... 1
1.2 The Clean Si(100)-(2x1) Surface................................ 3
1.3 Vacancy Structure................. 8
1.4 Diffusion Mechanisms............. 13
1.4.1 Data Analysis…………… 14
1.4.1.1 Unrestricted Random Walk........ 14
1.4.1.2 Arrhenius Relations............. 16
1.4.1.3 Jump Length Distributions....... 18
1.4.2 Transport Mechanisms.... 19
1.4.2.1 Hopping Mechanism............... 19
1.4.2.2 Vacancy-Mediated Diffusion Mechanism............................................. 20
1.4.2.3 Exchange Mechanism.............. 21
1.5 Literature Reviews............... 22
1.5.1 Cl-terminated Si(100)-(2x1) Surface.... 22
1.5.2 Case Studies-Vacancy Diffusions........ 24
1.5.3 Enhancement of surface diffusion with adsorbed H............................................ 29
1.5.4 Cl Extraction by H-atoms from Cl-terminated Si(100) Surface....................................... 30

Chapter 2 Experimental Setup......... 34
2.1 The Vacuum System................ 34
2.2 Scanning Tunneling Microscope (STM)....... 36
2.2.1 An Introduction........ 36
2.2.2 The STM System................................ 37
2.2.3 Principles of Electron Tunneling....... 38
2.3 Tip Preparation.................................. 40
2.4 Sample Preparation............................... 42



Chapter 3 Results and Discussion..... 43
3.1 The Dynamics of H-Hopping............................... 45
3.1.1 Motion of H atoms at Various Temperatures. 45
3.1.2 Arrhenius Plot and Activation Energy for the H-exposed Set......................... 59
3.2 Statistics of H-exposed Hoppings.............................. 61
3.2.1 Raw Data....................... 61
3.2.2 Preference of Hopping Movements............................. 63
3.3 Results on Non H-exposed Hoppings............ 70
3.4 Conclusion................................... 73

Chapter 4 Conclusions................ 74

Appendix A............................ 76
A.1 Previous Experimental Results. 76

Appendix B............................ 79
B.1 Flow Charts................. 79

References............................ 83

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