Characteristics of Si(111) surface with embedded C84molecules

A monolayer of fullerene molecules on Si(111) surfaces is fabricated in an ultrahigh vacuum chamber through a controlled self-assembly process. The characteristics of self-assembled Si(111) surfaces, including supramolecular structures, electronic density of states, the quantum confinement effect, field emission features, and optoelectronical properties with embedded C84 are determined by the use of an ultrahigh vacuum scanning probe microscope. The results revealed that such a silicon surface with embedded C84 has a wide band gap of [similar]3.4 eV, high emission efficiency and low turn-on voltage, all of which are crucial to nano-electronics, optoelectronics, and the fabrication of semiconductor carbide. The measured data derived from photoluminescence emission experiments further confirm the corresponding band gap value obtained from I–V curves. The theoretical results from first-principles calculations for the field enhancement factor are compared with experimental measurements

Atomistic nucleation sites of Pt nanoparticles on N-doped carbon nanotubes

[[abstract]]The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt–C and Pt–N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-like-N-doped CNTs.[[journaltype]]國外[[incitationindex]]SCI[[booktype]]紙本[[countrycodes]]GB

Characteristics and Nano-measurements of Fullerene Embedded Si(111) surface using Scanning Probe Microscopy

Elucidating the effect of size variation in nanoscale has also led to various and unique new physical and chemical properties in materials. Silicon carbide is one of the most important new-generation semiconducting materials, with important applications in various fields. Silicon carbide has promising development potential in the applications related to optoelectronic devices and high-temperature electric devices. Field emission properties of semiconductor carbides have motivated a number of studies because of their application for electron field emission sources. However, a high density of defects, such as micropipes and dislocations, commonly are present on conventional silicon carbide surfaces, potentially affecting the electronic structure, and causing device failure as well. As devices for silicon-based electronics industry are developing to the physical limits, it is urgency to find substituting materials. Fullerene molecules were used instead of carbon souces and silicon was taken as supporting substrate. The interface configuration and growth mode of fullerene molecules on silicon surfaces are very important as an understanding thereof may support the replacement of silicon carbide as a semiconductor material. In this work, the supramolecular structures and orientations of C60 and C84 molecules were studied under a UHV-scanning tunneling microscope. Carbon molecules preferentially appear in faulted halves, rather than in unfaulted halves and corner holes; they are embedded in silicon substrates. The orientations and possible configurations of C60 and C84 are considered in this work. The energy differences for various features of C60 and C84 molecules are estimated and discussed. This study also fabricates a single molecule, nanoclusters, and self-assembled layers of C84 on Si(111) surfaces using special annealing treatments. The electronic density of states related to quantum confinement effect and field emission properties are determined at room temperature using an ultra-high vacuum scanning tunneling microscope and a high-voltage source measurement unit respectively. Additionally, calculations from first-principles method are in good agreement with experimental results. The optoelectronical properties are examined by photoluminescence emission spectroscopy. The stiffness of the Si(111) surfaces with embedded C84 is determined from force-distance curve measurements made using an atomic force microscope in atmosphere environment and ultra-high vacuum respectively. This investigation develops a material with many advantages over conventional silicon carbides and without porous defects, which can therefore be used as a substitute in optoelectronic and electronic devices. We believe that our work has the advantages of conventional silicon carbides but also can avoid the porous defects, and thus is a substitute for optoelectronic and electronic devices. The self-assembled silicon surfaces with embedded C84 have favorable properties for applications in nanoelectronics and optoelectronics. The excellent characteristics of the developed material show nanotechnology consciousness through controlling matter on an atomic and nanoparticle scale. More important properties for fullerene embedded Si substrate will be revealed in the near future.奈米尺度下導致許多特性改變，其中碳化矽是重要的新世代材料，因其優異的物理及化學性質，而在不同領域擁有絕佳的應用。碳化矽擁有良好的光電性，可做光電、高溫應用，此外也擁有良好的場發射特性，因此也吸引眾多學者競相研究。然而，碳化矽有個重大天缺，即在表面常出現高密度的缺陷如微孔洞或錯位，甚至影響電子結構導致元件失效。隨著以矽為基底的元件已發展至物理極限，我們需迫切地研發替代性的材料。於是我們利用碳簇分子用來取代碳化矽中的碳，而Si為其支撐基底。 本文研究碳簇分子包括碳60與碳84在矽(111)-7x7表面上的內在結構及吸附位置。實驗發現在室溫下，較喜吸附在faulted half勝過unfaulted Half與corner hole，同時也對其活化能差探討。此外，有單顆、原子團、單層及多層的碳84分子層，再對其電學特性與場發射特性探討，也有利用原子力顯微鏡去探討其力學特性。 本研究所製造出的碳簇分子埋入矽(111)表面，不但擁有碳化矽的優點，但又能免除其缺陷多的缺點，適合應用在光電元件。研究成果在奈米電子與光電領域能有極佳的應用，可藉由控制原子及奈米粒子在奈米科技上有一席之地。相信在不久的將來，碳簇分子埋入矽基板將會有更多重要特性被發現。Table of Contents Abstract in English......................................................................................I Abstract in Chinese...................................................................................III Table of Contents......................................................................................IV List of Figures..........................................................................................VII List of Tables............................................................................................XII Chapter 1 Introduction..........................................................................1 1.1 Motivation...........................................................................................................1 1.2 Introduction of fullerene molecule......................................................................3 1.3 Organization of the dissertation...........................................................................7 Chapter 2 Apparatus and operating procedure........................................8 2.1 Scanning Tunneling Microscopy.........................................................................8 2.1.1 Introduction of STM................................................................................8 2.1.2 STM operating modes............................................................................10 2.2 Atomic Force Microscopy..................................................................................12 2.2.1Introduction of AFM................................................................................12 2.2.2 AFM operating modes............................................................................13 Chapter 3 Adsorption of fullerene molecules on Si(111)-7x7 surface...........................................................................................................................15 3.1 Introduction.......................................................................................................15 3.2 Deposition of fullerene molecules on Si(111)-7x7 surface...............................18 3.3 C60 adsorption on Si(111) -7x7 surface............................................................19 3.3.1 Adsorption sites of C60..........................................................................19 3.3.2 Intromolecular structures of C60............................................................24 3.4 C84 adsorption on Si(111) -7x7 surface............................................................27 3.4.1 Adsorption sites of C84..........................................................................27 3.4.2 Intromolecular structures of C84............................................................37 3.5 Conclusions and discussion...............................................................................40 Chapter 4 Self-assembled layers of fullerene molecules.......................41 4.1 Introduction.......................................................................................................41 4.2 Self-assembly mechanism.................................................................................44 4.3 Preparation of C84 self-assembled layers.........................................................46 4.4 Self-assembled C84...........................................................................................48 4.4.1 Low coverage deposition........................................................................48 4.4.2 High coverage deposition.......................................................................51 4.5 Conclusions and discussion...............................................................................59 Chapter 5 Nano-measurements of Si(111) surface with embedded C84 molecules..............................................................................................................60 5.1 Introduction.......................................................................................................60 5.2 Field emission theory.........................................................................................62 5.3 Experiment.........................................................................................................65 5.4 Electrical properties measurements...................................................................67 5.4.1 I-V characteristics determined using UHV-STM...................................67 5.4.2 Field emission characteristics determined using UHV-STM.................74 5.4.3 Conventional field emission characteristics...........................................82 5.5 Photoluminescence characteristics....................................................................86 5.6 Mechanical properties determined using AFM in atmosphere and ultra-high vacuum..............................................................................................................88 5.7 Conclusions and discussion...............................................................................93 Chapter 6 Conclusions and Prospects.........................................................94 Reference........................................................................................................................96 Publication Lists.................................10

Investigation of C60 and C84 on Si(111)-7x7 Surface with Scanning tunneling Microscopy

藉由超高真空掃描穿隧顯微鏡，我們觀察到碳六十分子與碳八十四分子吸附在矽（111）- 7×7重構表面上不同吸附位置的吸附軸向。我們利用K-cell 蒸鍍槍分別在410℃及500℃將碳六十分子與碳八十四分子蒸鍍到矽（111）- 7×7重構表面，實驗結果發現碳六十分子與碳八十四分子有較高的機率吸附在faulted半單位晶胞、次高的機率吸附在unfaulted半單位晶胞上，兩個吸附位置的吸附機率合計約90％左右; 而吸附在corner hole上的機率相對較少，約10％左右。藉由比較碳六十與碳八十四吸附在矽(111)-7×7重構表面上與在自由空間中的形貌大小，我們認為碳六十與碳八十四吸附在矽表面是呈現鬆弛的現象。而在觀測碳六十與碳八十四在矽(111)-7×7重構表面上的不同吸附位置及吸附軸向方面，我們觀測到碳六十呈現五環的結構，而碳八十四則大多為平躺吸附在矽表面上。 本實驗使我們初步瞭解碳簇分子吸附在矽(111)-7×7重構表面上的吸附軸向，這樣的實驗結果對於後續研究碳八十四的量子效應是有助益的。未來的研究若能結合理論上的分析必定能更進一步清楚地瞭解碳簇分子的吸附軸向及其鍵結結構。Using ultra-high vacuum scanning tunneling microscope(UHV-STM), we study the adsorption orientation of C60 and C84 on Si(111)-(7 x 7) surfaces at different adsorption sites. The adsorption of C60 and C84 on Si(111)-(7 x 7) surfaces, deposited by K-cell evaporator at 400℃ and 510℃ respectively, are found to be adsorbed in faulted half unit cell at room temperature preferentially, but can be found in unfaulted half unit cells and in corner holes also. Comparison of the models of C60 and C84 molecules with free space, we believe that C60 and C84 molecules are relaxed on Si(111)-(7 x 7) surfaces. We also find that the C60 adsorbed on Si(111)-(7 x 7) surfaces as a bright pentagon with several curves, and C84 often adsorbed horizontally on Si(111)-(7 x 7) surfaces. The results presented in this work are essential to the understanding of the adsorption of C60 and C84 molecules on Si(111)-(7 x 7) surfaces. Since we would interest in quantum effect of C84 on Si(111)-(7 x 7) surfaces, the combination of theoretical analysis and experiment is important in future work.第一章 序論 1-1 簡介................................................1 1-2 矽(111)-7×7重構表面背景介紹...........................4 1-3 碳六十和碳八十四背景介紹...............................8 第二章 掃描穿隧顯微鏡原理與儀器介紹 2-1 掃描穿隧顯微鏡原理...................................15 2-1-1 STM 簡介.........................................15 2-1-2 穿隧原理..........................................16 2-1-3 取像模式..........................................19 2-1-4 壓電材料..........................................21 2-2 儀器介紹............................................24 2-2-1 真空系統..........................................24 2-2-2 電子及控制系統.....................................30 2-2-3 避震系統..........................................34 2-2-4 探針的製備.........................................37 2-2-5 樣品的製備.........................................40 第三章 結果與討論 3-1 矽(111)-7×7重構表面..................................43 3-2 碳六十在矽(111)-7×7重構表面上的吸附現象................46 3-2-1 碳六十不同吸附位置的探討............................46 3-2-2 碳六十吸附軸向的探討................................51 3-3 碳八十四在矽(111)-7×7重構表面上的吸附現象...............58 3-3-1 碳八十四不同吸附位置的探討...........................58 3-3-2 碳八十四吸附軸向的探討...............................71 第四章 統整與結論.........................................78 參考文獻.................................................8

METHOD OF FORMING SELF-ASSEMBLED AND UNIFORM FULLERENE ARRAY ON SURFACE OF SUBSTRATE

本發明提供一種於基板表面生成自組裝且高度均勻之碳簇分子陣列的方法,其包括以下之步驟:(1)提供一基板;(2)在真空環境下將該基板加熱至約200℃至約1000℃;及(3)提供一碳簇分子奈米粉末,並在該真空環境下藉由物理氣相沈積法將該碳簇分子奈米粉末沈積在該基板表面上,從而於該基板表面上形成自組裝且高度均勻之碳簇分子陣列。本發明亦提供一種由此製得之碳簇分子陣列嵌入式基板,其具有優異之場發射性能,可作為場發射器用於任何場發射顯示器(Field Emission Display;FED)中。最後,本發明亦提供一種由此製得之碳簇分子陣列嵌入式基板,其可替代碳化半導體材料,作為光電元件及高溫、高功率、抗高溫或高頻率電子元件之用

METHOD OF FORMING SELF-ASSEMBLED AND UNIFORM FULLERENE ARRAY ON SURFACE OF SUBSTRATE

本發明提供一種於基板表面生成自組裝且高度均勻之碳簇分子陣列的方法，其包括以下之步驟：(1)　提供一基板；(2)　在真空環境下將該基板加熱至約200℃至約1000℃；及(3)　提供一碳簇分子奈米粉末，並在該真空環境下藉由物理氣相沈積法將該碳簇分子奈米粉末沈積在該基板表面上，從而於該基板表面上形成自組裝且高度均勻之碳簇分子陣列。本發明亦提供一種由此製得之碳簇分子陣列嵌入式基板，其具有優異之場發射性能，可作為場發射器用於任何場發射顯示器(Field Emission Display；FED)中。最後，本發明亦提供一種由此製得之碳簇分子陣列嵌入式基板，其可替代碳化半導體材料，作為光電元件及高溫、高功率、抗高溫或高頻率電子元件之用

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The characteristics of the C84-embedded Si surface, such as atomic resolution topography, local electronic density of states, band gap energy, field emission properties, nanomechanical stiffness, and surface magnetism, were examined using a variety of surface analysis techniques under ultra, high vacuum (UHV) conditions as well as in an atmospheric system. Experimental results demonstrate the high uniformity of the C84-embedded Si surface fabricated using a controlled self-assembly nanotechnology mechanism, represents an important development in the application of field emission display (FED), optoelectronic device fabrication, MEMS cutting tools, and in efforts to find a suitable replacement for carbide semiconductors. Molecular dynamics (MD) method with semi-empirical potential can be used to study the nanoindentation of C84-embedded Si substrate. A detailed description for performing MD simulation is presented here. Details for a comprehensive study on mechanical analysis of MD simulation such as indentation force, Young's modulus, surface stiffness, atomic stress, and atomic strain are included. The atomic stress and von-Mises strain distributions of the indentation model can be calculated to monitor deformation mechanism with time evaluation in atomistic level

The roles and mechanism of IFIT5 in bladder cancer epithelial-mesenchymal transition and progression

The prognosis of bladder cancer (BCa) depends on several key factors including anatomical site, tumor grade, and stage. In general, muscle-invasive bladder cancer (MIBC) is associated with higher incidence of distant metastasis compared with Non-muscle-invasive bladder cancer (NMIBC). Treatment outcome of the patients with metastatic BCa has been very poor with ~15% of overall survival rate. Thus, it is apparently important to understand the underlying biology for metastatic progression of BCa. Although epithelial–mesenchymal transition (EMT) has long been implicated in BCa metastasis and treatment resistance, the underlying mechanism is not fully understood. In this study, we have identified that the expression of interferon induced protein with tetratricopeptide repeats 5 (IFIT5) is positively correlated with pathological characteristics, and predicts a poor prognosis of BCa patients. Since the function of IFIT5 in BCa has not yet been characterized, we demonstrate that IFIT5 can induce EMT, promote cell migration and invasion, and increase the expression of ICAM1 in BCa via down-regulation of mature miR-99a. Moreover, ICAM1 is shown as a direct target of miR-99a. Overall, we conclude that IFIT5 is a new oncogene in BCa

Helicity-dependent terahertz radiation from topological insulator Sb<inf>2</inf>Te<inf>3</inf> thin film by femtosecond optical excitation

We report on terahertz radiation from topological insulator (TI) Sb2Te3 thin film under ultrafast optical excitation with different helicity. Polarity-reversals of the emitted THz radiation were observed as the helicity of optical pulses reversed. The observed phenomena are coincident with the characteristics of the helicity-dependent photocurrent on TIs. Our work demonstrates the potential applications of surface photocurrents on TIs for opto-spintronics devices