利用蒸鍍沉積外來原子調控準獨立鍺烯的形成

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研究生：	陳亭宇 Chen, Ting-Yu
論文名稱：	利用蒸鍍沉積外來原子調控準獨立鍺烯的形成 Triggering the formation of quasi-freestanding germanene by foreign-atoms deposition
指導教授：	唐述中 Tang, Shu-Jung
口試委員:	鄭澄懋 Cheng, Cheng-Maw 鄭弘泰 Jeng, Horng-Tay
學位類別：	碩士 Master
系所名稱：	理學院 - 物理學系 Department of Physics
論文出版年：	2018
畢業學年度：	106
語文別：	英文
論文頁數：	69
中文關鍵詞：	鍺烯、銀(111)
外文關鍵詞：	germanene, Ag(111)
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石墨烯的發現激起大家對於相關二維材料研究的極大興趣，包含最直覺的與碳元素同為第四族元素的鍺所構成的鍺烯。本論文的基礎建立於鍺烯在銀(111)上的兩個不同相，其一為條紋相(striped phase)，它結構的其中一個方向被拉長以與銀基底的晶格長度相稱；另一個相為準獨立相(quasi-freestanding phase)，它與理論上的獨立鍺烯相近，但與銀基底晶格長度有著較大的差異，因此較為無序。我們以角解析光電子能譜、低能量電子繞射儀和掃描穿隧式顯微術來研究一個有趣的想法：利用蒸鍍沉積外來原子調控準獨立鍺烯的形成。適當選擇的外來原子如同界面活性劑，若它能不破壞鍺烯的結構，反而促使條紋相鍺烯的張力被釋放，形成準獨立鍺烯，並且藉由夾擠作用使準獨立鍺烯更為穩定有序。我們以鉛做為外來原子，於鍺烯在銀(111)的樣品上進行一系列的實驗，其結果啟發也驗證了我們的想法，這樣的機制也可望有更廣泛的用途。

The discovery of graphene has spurred great interest in the exploration of novel 2D materials, including the intuitive graphene’s siblings, germanene, made of group IV element Ge. This work is the further study of the single-layer dual germanene phases on Ag(111). One such phase, striped phase (SP), is tensile strained and partially commensurate with the substrate. The other, a quasi- freestanding phase (QP), which is very close to the freestanding germanene predicted by the first-principles calculation, fully relaxes the tensile strain at the cost of more lattice mismatch. The interesting idea of this study is triggering the formation of QF germanene from SP germanene by foreign-atom deposition. The experimental techniques such as low energy electron diffraction (LEED), angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) were employed in the research of this thesis. Foreign atoms, as surfactants, play a role in relaxing the tensile strain of SP germanene, and stabilizing the QP germanene by squeezing effect. We have done a series of experiments using Pb as the foreign atom to verify not just the idea but the very interesting mechanism.

Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 2 Basic background knowledge . . . . . . . . . . . . . . . . 3
1 Crystal structure. . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Ag(111) . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
1.2 Reciprocal lattice . . . . . . . . . . . . . . . . . . . . . . 7
1.3 Honeycomb structure . . . . . . . . . . . . . . . . . . . . . 10
2 Surface and superstructure . . . . . . . . . . . . . . . . . . .11
2.1 Surface Brillouin Zone . . . . . . . . . . . . . . . . . . . .11
2.2 Surface state . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3 Wood’s notation . . . . . . . . . . . . . . . . . . . . . . . 13
2.4 Monolayer . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.5 Moiré pattern . . . . . . . . . . . . . . . . . . . . . . . . 14
3 Photoemission Spectroscopy . . . . . . . . . . . . . . . . . . .15
3.1 Photoelectron effect . . . . . . . . . . . . . . . . . . . . .15
3.2 Basic principle . . . . . . . . . . . . . . . . . . . . . . . 16
3.3 Angle-Resolved Photoemission Spectroscopy . . . . . . . . . . 18
4 Scanning tunneling microscope . . . . . . . . . . . . . . . . . 21
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . .21
4.2 Scanning tunneling spectroscopy . . . . . . . . . . . . . . . 21
Chapter 3 Introduction to experimental Instruments . . . . . . . . .23
1 Ultra High Vacuum system . . . . . . . . . . . . . . . . . . . .23
2 Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . .  24
3 Low Energy Electron Diffraction . . . . . . . . . . . . . . . . 26
4 Source of photons . . . . . . . . . . . . . . . . . . . . . . . 27
4.1 Helium lamp . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2 Synchrotron radiation . . . . . . . . . . . . . . . . . . . . 28
5 Energy analyzer . . . . . . . . . . . . . . . . . . . . . . . . 29
Chapter 4 Introduction to the single-layer dual germanene phases
on Ag(111) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
1 The growth of Germanium on Ag(111) . . . . . . . . . . . . . . .32
1.1 Preparation of samples . . . . . . . . . . . . . . . . . . . .32
1.2 The three evolving stages . . . . . . . . . . . . . . . . . . 32
2 “Striped phase” germanene . . . . . . . . . . . . . . . . . . . 38
3 “Quasi-freestanding phase” germanene . . . . . . . . . . . . . .42
4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Chapter 5 Triggering the formation of germanene by depositing
foreign atoms . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
1 Basic idea . . . . . . . . . . . . . . . . . . . . . . . . . . .49
1.1 The overnight evolution . . . . . . . . . . . . . . . . . . . 49
1.2 Model of the idea . . . . . . . . . . . . . . . . . . . . . . 50
2 Results and discussion of the experiments . . . . . . . . . . . 51
2.1 Experimental parameters . . . . . . . . . . . . . . . . . . . 51
2.2 Deposition of Pb on the 0.9-ML Ge-Ag(111) . . . . . . . . . . 52
2.3 Deposition of Pb on the 0.5-ML Ge-Ag(111) . . . . . . . . . . 55
2.4 An experiment of inverse deposition order . . . . . . . . . . 59
Chapter 6 Conclusion and Outlook . . . . . . . . . . . . . . . . . .66
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . .68

                                

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