臺灣博碩士論文加值系統

在這論文中, 我們研究單晶表面上自組毫微米結構, 包括在Si(111) 表面
上成長的Ga結構, 及在Mo(111)表面上吸附物引發的小錐面.

我們使用可變溫的掃描穿隧顯微鏡, 研究在真空中Si(111)單晶表面上Ga
所成長的結構. 在200*C時, 我們觀察到二維奇異粒子團, 這是二維奇異
粒子團第一次被直接看到. 這些奇異粒子團是三角形, 且有特別方向偏
好, 而它們的奇異數是n(n+1)/2, 其中n是三角形一邊的原子個數. 我們
提出一個模型來解釋奇異粒子團的方向偏好, 及伴隨在奇異粒子團周圍的
特徵晶格空洞, 及十粒團特別多特別穩定. 我們提出另外一些模型來解釋
為何看到的奇異粒子團都是三角形.

當加溫到300*C~450*C時, 由奇異粒子團(凝結核)逐漸粗粒化形成較大的
粒子團, 其間影響速率的關鍵步驟是第一個原子脫離十粒團這一步.
在450*C時, 我們觀察到有準周期錯位的非整數比毫微米碎晶體. 我們提
出一個對應正三角形毫微米晶體的模型, 從這模型中可看出原本位於緊臨
粒子團的Ga原子將會參加粒子團組構, 而留下一晶格空洞及一Si懸鍵.

我們使用X-ray光電子能譜, Auger電子能譜, 粒子熱脫附溫譜, 及低能
量電子繞射圖像, 研究在真空中單層Pd,金,及氧對Mo(111)單晶表面結構
穩定性的影響. Pd及氧分別會引發形成{112}及{447}小錐面, 而兩者在高
溫時都有可逆的"小錐面/平面"相變, 不過這相變隨溫度的上下來回都有
滯後現象. 金無法在Mo(111)表面引發小錐面, 但其可在臨近的表面引發
{112}錐面與(111)表面的混合. 這些結果的含意將與目前關於吸附物引發
小錐面之機制的推想作比較.

In this thesis, we have studied self-organization of special
nano-structures on single crystal surfaces: the growth of Ga
structures on Si(111) surface and adsorbate induced facet
formation on Mo(111) surface.

The growth of gallium nanostructures on the reconstructed
3×3 Ga/Si(111) surface has been studied using a variable
temperature scanning tunneling microscope (STM). At 200*C, two
dimensional magic clusters with preferred orientation have been
directly observed for the first time. The magic numbers are n(
n+1)/2, where n (2,3,4, or 5) is the number of atoms on each
side of these triangular clusters.

A structural model is proposed to account for the cluster
orientation and lattice vacancies as well as the extraordinary
abundance and stability of the decamers (n=4). Another
structural models of clusters are proposed to account for the
triangular shape of magic clusters.

This system then evolves from magic clusters (nucleation
centers) into larger clusters by coarsening process at
300*C~450*C, the rate controlling step may be the first atom
escaping from a decamer.

At 450*C, incommensurate nanocrystals with quasi-periodical
dislocations are observed in Ostwald ripening. A structural
model of a large equilateral triangular nanocrystal is
proposed, which suggests each adatom lattice Ga atom next to a
cluster will attend cluster formation while leave one Si
dangling bond in surrounding lattice.

The influence of about a monolayer coverage of Pd, Au, and
oxygen on the structureal stability of the Mo(111) surface has
been studied under high vacuum (UHV) using X-ray photoemission
spectroscopy(XPS), Auger electron spectroscopy(AES),
temperature programmed thermal desorption spectroscopy(TDS) and
low energy electron diffraction (LEED).

Pd and oxygen are found to induce the formation of {112} and
{447} oriented facets respectively on the substrate surface.
Both surface undergo a reversible "faceted/planar" phase
transition at higher temperatures and the transition shows
intrinsic hysteresis in both cases. With Au coverage, the
precisely oriented Mo(111) surface is stable, whereas the
vicinal surfaces can be induced to form a mixture of {112}
facets and the original (111) surface.

The implication of these results to the existing conjecture
about the mechanism of adsorbate-induced faceting is discussed.

COVER
Contents
Chap 1 Introduction
Chap 2 Instruments
2.1 STM brief review
2.1.1 Historical remarks of electron tunnelin
2.1.2 Mode of STM opeartion
2.1.3 Relative Developments of STM
2.2 LEED brief review
2.2.1 Historical finding of electron diffraction
2.2.2 LEED operation
2.3 Setup of STM system
2.3.1 UHV system
2.3.2 STM
2.3.3.Preparation of STM tips
2.3.4 Preparation of 7x7 si(111) surface
Reverences
Chap 3 Growth of Ga Structures on Si(111) surface:from magic cluster muclei to incommensurate nanocrystals
3.1 Introduction
3.2 Experiment
3.3 Results
3.4 Discussion
3.4.1 Structures of magic clusters
3.4.2 Structure of incommensurate nanocrystals
3.4.3 Growth process
3.5 Conclusion
3.6 Appendixes
3.6.1. Screw dislocations observed on si(111)surface
3.6.2. Three degenerate domains of √3 x √3 Ga/Si(111)
3.6.3. Persolating clusters of 6.3 x 6.3 Ga/Si(111)
3.6.4. Protrusions
References
Chap 4 Faceting phase transition of Mo(111)induced by Pd, Au, and oxygen overlayer
4.1 Introduction
4.2 Experiment
4.3 Results
4.3.1 Pd/Mo(111)
4.3.2 Au/Mo(111)
4.3.3 O/Mo(111)
4.4 Discussion
4.4.1 Correlation between electronegtivity and faceting
4.4.2 Hysteresis in the planar/faceted phase transition
4.4.3 Phase separation during the facet formation
4.5 Conclusion
Reference