有機場效電晶體(OFET)具有比傳統矽基場效電晶體(FET)更多的優點像是：彈性與柔軟性、可與大面積基底相容和低溫製程。[n]Phenacene 代表有n個苯環，每個苯環都以w形狀相連，苯環上下的π電子軌域都在同一平面上。要在場效電晶體中形成通道，π電子軌域扮演重要的角色。有研究指出，由於phenacene高電子移動率，phenacene可以用來做OFET。此外，[5]phenacene（也叫做picene）在某些參雜條件下會轉變成超導體。[5]phenacene的超導溫度會被參雜物的位置所影響，這個特性吸引許多科學家的注意。若要更進一步的探討超導現象，對於電子結構與分子結構的深度理解是必要的。在此論文中，我們在低溫下，用穿隧掃瞄電子顯微鏡(STM)探討[7]phenacene在Ag(111)表面上的結構。
[7]phenacene跟picene結構相似，也在高溫下有高的遷移率。在氮氣的沸點下，我們發現 [7]phenacene的遷移率仍然很高。分子在第一層會移動、翻轉和重疊。我們對於一個分子進行數小時的觀察。我們的結果顯示[7]phenacene薄膜在0.24 nm的厚度下是屬於多層的。而這個發現與之前的picene是不相符的。

Organic field-effect transistors (OFET) possess several advantages in comparison to silicon-based, classical field-effect transistors (FET), such as mechanical flexibility, compatibility with large area substrate and low temperature fabrication. [n]Phenacenes represent a class of molecules which contain n benzene rings (n ≥ 3) arranged in a repeating W-shaped pattern within the same plane with π-electrons above and below its plane. π-electrons are important for forming conductive channels in FETs. It was reported that phenacenes can be a candidate of for OFETs because of its high hole-mobility. Moreover, [5]phenacene, also called Picene, can be a superconductor under specified doping conditions. It attracts many researchers’ attention because of its high transition temperature affected by the position of dopants. For further progress, a precise investigation of the electronic structure and molecular growth is necessary. Here, we investigated the structure of [7]phenacene adsorbed on the surface of Ag(111) by scanning tunneling microscope (STM) under low temperature. [7]phenacene has a very similar structure to picene and [7]phenacene has a high mobility at room temperature. Below the boiling point of nitrogen, we found that the mobility of [7]phenacne is high at sub-monolayer coverage. Molecules are flipping, moving and climbing on the first layer. We followed individual molecules and their motion over an extended period of time, i.e. hours. Our results suggest that the structure of thin films with about 0.24 nm thickness are multilayers of [7]phenacene. This experimental observation is in contrast to the previous interpretation for the growth of Picene.

摘要 i
ABSTRACT ii
TABLE OF CONTENTS iv
Chapter 1 Introduction 1
1. 1. Motivation 2
1. 2. Literatures Review 3
1. 2. 1. Thickness and Substrate Dependent Thin Film Growth of Picene and Impact on the Electronic Structure 3
1. 2. 2. Structural and electronic properties of ultrathin picene films on the Ag(100) surface 9
1. 2. 3. Scanning tunneling microscopy/spectroscopy of picene thin films formed on Ag(111) 12
Chapter 2 Low-Temperature Ultra High Vacuum System 16
2. 1. Vacuum 16
2. 1. 1. Pumps 17
2. 1. 2. Pumping Procedure 20
2. 2. Low Temperature System Setup 22
2. 3. Principal of STM 24
2. 3. 1. Tunneling Effect 24
2. 3. 2. Instrumentation 28
2. 4. Tip Preparation and Modification 31
2. 5. Sample Preparation 31
2. 5. 1. Argon Sputtering 32
2. 5. 2. Annealing 32
2. 5. 3. Molecular deposition 32
2. 6. Data correction 33
2. 6. 1. Creep 33
2. 6. 2. Drift 34
2. 6. 3. Noise 36
Chapter 3 STM Results 40
3. 1. Topographies and profiles 40
3. 1. 1. Ag(111) surface 40
3. 1. 2. Submonolayer of [7]phenacene 42
3. 1. 3. [7]phenacene thin films 45
3. 2. Spectroscopy 76
Chapter 4 Discussion and Analysis 77
Chapter 5 Conclusions 86
REFERENCES 87
APPENDIX 93

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