1,720,975 research outputs found
Electron transport in In-rich InxGa1-xN films
No full text本論文主要是探討多銦氮化銦鎵薄膜InxGa1-xN (x = 1, 0.98, 0.92,
0.8, 0.7) 的電子傳輸性質。我們測量了大溫度範圍下氮化銦鎵的電子
傳輸特性。我們發現在實驗誤差範圍內，樣品的載子濃度在測量的溫
度範圍內幾乎與溫度無關，這是金屬的行為。此外我們利用van der
Pauw 四點量測法計算樣品的電阻率。綜合電阻率與載子濃度的數據
顯示，我們的樣品隨著鎵的成分上升，有一個由金屬到半導體的轉
變。我們也計算了樣品的載子遷移率，載子遷移率在整個量測的溫度
範圍內，隨著鎵成分的升高而降低，這也印證了氮化銦的傳輸特性優
於氮化鎵。由於金屬電阻率在低溫下遵守Bloch T5 定理，對於銦濃
度大於等於92% 的樣品，我們檢查了它們的電阻率與Bloch T5 定
理的符合程度。分析的結果顯示高銦成分的樣品的電阻率非常符合
Bloch T5 定理，從而進一步的支持了高銦濃度的氮化銦鎵薄膜傳輸特
性與金屬十分類似。This thesis focuses on electron transport properties in InxGa1−xN (x =1,
0.98, 0.92, 0.8, 0.7) thin films. We have performed transport measurements
on InxGa1−xN thin films over a wide temperature range. We observed that
within experimental error, the carrier densities are temperature independent.
Besides, the resistivities, combined with the carrier densities, show
a tendency of transition from metal to semiconductor with increasing Ga
composition. The calculated mobility shows that for metallic like samples
(InxGa1−xN with x ≥0.92), the dominant scattering mechanism is the imperfection
scattering over the whole temperature range. We also showed
that Bloch T5 curves fit very well the resistivities of samples InxGa1−xN
with x =1, 0.98, 0.92, once again supporting that very high In composition
InxGa1−xN films can be considered as degenerate electron systems in which
the Fermi level is much higher than conduction-band bottom over the whole
measurement range.1 Introduction 1
2 Theoretical background 4
2.1 Classical Hall effect . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Van der Pauwmethod . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Electrical transport properties . . . . . . . . . . . . . . . . . . 10
2.3.1 Ohm’s law and electrical conductivity . . . . . . . . . . 10
2.3.2 Relaxation time approximation . . . . . . . . . . . . . 12
2.3.3 The temperature-dependent electron resistivity of metals 14
3 Sample fabrication and Hall measurements 20
3.1 Sample fabrication . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.1 Metal-organic vapor phase epitaxy . . . . . . . . . . . 20
3.1.2 Sample structure . . . . . . . . . . . . . . . . . . . . . 21
3.2 Hall measurements . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2.1 Experimental setup . . . . . . . . . . . . . . . . . . . . 23
3.2.2 Ohmic contacts . . . . . . . . . . . . . . . . . . . . . . 23
3.2.3 Elimination of background voltage . . . . . . . . . . . 25
4 Electrical properties of In-rich InxGa1−xN films 27
4.1 Deviation of the Rxy fromzero at zero magnetic field . . . . . 27
4.2 Temperature dependence of carrier density, resistivity and mobility
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.3 Curve fitting of Bloch T5 law . . . . . . . . . . . . . . . . . . 38
5 Conclusions 42
Bibliography 4
Design of Mixers for Microwave and Millimeter-wave Applications
No full text本論文主要是在討論被動的平衡式次諧波混波器、利用改良的平衡不平衡器以實現在高頻的寬二極體頻混波器以及架構上較為簡單的閘極驅動單端次諧波混波器。主要研究方向在於如何以較低的本地振盪訊號即可驅勳混波器達成混波效果。
此論文共分三個部份皆為被動式的混波器，在第一部份中先討論並設計一於pHEMT 製程上的71-76 GHz平衝式閘極驅動次諧波混頻器並利用相同架構的混波器作為基本元件實現一60 GHz 的解調變器；第二部份則是介紹一用於天文觀測所需的高頻混波器，矽基材料所製作的電晶體之最大振盪頻率不夠高，在高頻時已無法提供應有的增益，所以這類高頻電路常會以砷化鎵作為實現的材料但是由於基板厚度較厚，以微帶線在高頻實現馬遜平衡轉非平衡器時會受到接地不良的影響而導致其特性不佳，所以在這一部份藉由增強耦合強度來改進此一問題，進而使整體電路更加對稱增加設計上的方便性；第三部份是設計並實現一CMOS單端的閘極驅動次諧波混波器，由於沒有使用平衡轉非平衡器，其面積可以較為縮減。雖然沒有平衡轉非平衡器，但是在利用耦合線當作共振腔來作為濾波器之後隔離度也有相當的改善。將汲極和基座相接可以抑制在中頻輸入信號強度增加時所造成的直流位準漂移，因為只用到一個電晶體，所以只需要約0 dBm即可推動此混波器波減少系統中其他電路的負擔。This thesis discusses an gate-pumped resistive sub-harmonic mixer, high frequency broadband diode mixer with improved balun in high frequency and a single-ended gate-pumped sub-harmonic mixer. The main purpose is to reduce the level of LO power needed to drive a mixer.
This thesis consists of three parts and they are all passive mixer in common. The first part introduced a 71-76 GHz balanced resistive gate-pumped mixer using in pHEMT process. Based on this topology, a 60 GHz demodulator is also presented. In the second part, a high frequency diode mixer for space observation is realized. Because the MOSFET fabricated by Si-based material has no gain in such high frequency, the circuits in high frequency usually are implemented in GaAs process. However the thickness of the substrate in these processes is large and may corrupt the ideal ground needed in Marchand balun. A modified Marchand balun which has better coupling factor and resists non-ideal ground effect is introduced in this part to enhance the symmetry of the circuit and relieve the design difficulty. A single-ended gate-pumped sub-harmonic mixer is designed and presented in part three. Without the baluns, the size of the mixer can be more compact than balanced mixers. Although there is no balun, the isolation can still be achieved by filter using coupled-line resonator which is more compact than a balun. Connecting drain to body can help the problem that dc voltage of drain changes. Due to its simple topology, this mixer can be driven with LO power of about only 0 dBm, and eases the requirement of other components in the system
Experimental Study on the Near-Wall Brownian Behavior of High Volume Fraction Nano Particles using TIRF-enhanced PTV
No full text近年來由於科技的進步，結合微機電與生醫技術的生醫感測元件因應而生，而由布朗運動為理論基礎，所建立的新式檢測技術則為本實驗室近年來之目標，此類元件具有操作簡易、製作簡單且價格便宜之優點。於本研究中，針對布朗運動於微流道中運動現象作完整探討，包括布朗運動與邊界距離之討論、邊界表面性質與布朗運動之影響、濃度變化對布朗運動的影響以及環境溶液對於布朗運動之影響，希望可藉由本研究對此新式感測技術進行最佳化設計。本研究進行方式是藉由使用非螢光奈米粒子模擬高濃度情況，再以低濃度螢光粒子置入樣品中以便以粒子追蹤測速儀(PTV)作分析，並且搭配不同環境溶液、表面性質模擬可能遇到之情況。
從實驗中可以看出粒子靠近邊界時受到邊界的影響，布朗運動擴散係數會下降；當樣本中的粒子濃度提高時，直觀來看粒子間的碰撞機率增加導致能量消散更多，造成布朗運動速度下降。此外，表面性質的改變也會使布朗運動擴散係數發生變化，在未來可將此結果應用於建立在布朗運動理論下之新式生醫檢測中，有助於增加其準確度。In recent years, due to advances in technology, combined with MEMS and biomedical sensing element appeared. Base on the theory of Brownian motion, we established new bio-sensing technology in recent years. Such element has advantages that it’s simple to use, make and low price. In this study, we discuss the phenomena for the Brownian motion in micro-flow channel, including studies on the near-wall Brownian behaviors of particles, high volume fraction effect, how surface modification effects Brownian motion and how environmental solution effects Brownian motion, hope that by this study, we can improve this new sensing technology for optimal design. We use non-fluorescent nanoparticles to simulated high concentrations and use fluorescent particles in low volume fraction to trace the fluid, then use micro-Particle Tracking Velocimetry (PTV) for analysis. Then we change the environmental solutions, do surface modification and mixing different size of particles to simulate the conditions that may be encountered.
From the study, we know that the diffusion coefficient of Brownian motion decreases as the particles near the boundary and high volume fraction. Furthermore, surface modification and sample made by different particles size also change particles Brownian behavior, hope that the results of the study can be used in the Brownian motion-based bio-sensing technology and increasing its accuracy.口試委員會審定書 #
致謝 i
摘要 ii
Abstract iii
目錄 iv
表目錄 vii
圖目錄 viii
符號目錄 xi
第一章 緒論 1
1-1 前言 1
1-2 研究動機與目的 2
1-3 研究方法 3
1-4 論文架構 3
第二章 文獻回顧 5
2-1 布朗運動、邊界效應以及體積濃度影響文獻回顧 5
2-2 全反射螢光顯微技術文獻回顧 6
2-3 粒子影像測速儀/粒子追蹤測速儀文獻回顧 7
第三章 布朗運動 9
3-1 布朗運動及其數學模型 9
3-1-1 前言 9
3-1-2 愛因斯坦關係式 10
3-1-3 朗之文方程式 12
3-2 布朗運動與邊界效應之影響 13
3-3 布朗運動與體積濃度之影響 15
3-4 膠體粒子的布朗運動與沉降平衡 16
第四章 實驗設備與實驗方法 18
4-1 全反射螢光顯微技術 18
4-1-1 前言 18
4-1-2 漸逝波原理介紹 18
4-1-3 螢光粒子的非等向性放射 20
4-1-4 中間層分析 20
4-1-5 全反射螢光顯微鏡 21
4-2 微粒子影像/追蹤測速儀 21
4-2-1 原理 21
4-2-2 微粒子影像/追蹤測速儀實驗設備 23
4-2-2-1 光源裝置................................................................................23
4-2-2-2 影像擷取裝置 24
4-2-2-3 光學顯微鏡 24
4-2-2-4 同步器 24
4-2-2-5 影像分析軟體 25
4-2-2-6 光學路徑架構 25
4-3 咖啡環效應與觀測腔體製作 25
4-4 全反射螢光顯微技術之漸逝波照明深度量測實驗 26
4-5 高濃度奈米粒子樣本配製 26
4-6 視野校正 27
4-7 玻片表面改質 28
第五章 實驗結果與討論 30
5-1 微粒子追蹤測速儀與布朗運動分析 30
5-1-1 影像擷取與視野校正 30
5-1-2 螢光粒子濃度參數之決定 31
5-1-3 其餘觀測限制 32
5-1-4 粒子布朗運動分析 32
5-2 布朗運動與邊界效應之研究 33
5-3 布朗運動與濃度變化之研究 34
5-4 布朗運動與環境溶液之研究 35
5-5 布朗運動與表面改質之研究 36
第六章 結論 37
6-1 結論 37
6-2 未來展望 38
參考文獻 4
An Impedance-Transformation Embedded Sequential Rotation Feeder for Broadband Circularly Polarized Antenna Array
No full text本論文主要研究序列式旋轉饋入電路及其在天線陣列之應用。本論文前半段先針對現有文獻中有關序列式旋轉饋入電路之研究進行分析與整理，並深入探討其物理機制與等效電路，使吾人掌握其設計技巧與效能特性；接著以此基礎，提出一個新的公式及設計方法，並以實作量測獲得驗證。後半段則延續論文前半段的推導，探討天線元件與序列式旋轉饋入電路之間的作用關係，進一步提出一個適合序列式旋轉技巧的天線，以搭配前半段提出的新型序列式旋轉電路設計，實現在正向輻射圓極化增益3dB頻寬為49%，軸長比頻寬達46%的圓極化天線陣列。模擬與量測結果也都顯示相當一致。This thesis presents a study of sequential rotation feeder and its applications for circularly polarized antenna array. In the first half of this thesis, we survey several approaches of sequential rotation feeder network in the literature and analyze the principle and design techniques. Using an equivalent circuit model, we develop a new method on designing a compact sequential rotation feeder with the impedance transformer embedded. In the second half of this thesis, we investigate the effects of the imperfect impedance matching between the antenna elements and the sequential rotation feeder network. It is found that an antenna element with broadband minimum reactance is more suitable for the sequential rotation feeder. Furthermore, we illustrate the proposed method with two prototypes of PCB antenna arrays. The promising results are achieved, including the 3-dB axial ratio bandwidth around 46% and the co-polarized 3-dB gain bandwidth about 49% in the broadside of the antenna array. The simulation and experimental results also show a good agreement in this study.口試委員會審定書……………………………………………………… i謝 …………………………………………………………………… ii要 ……………………………………………………………………iiibstract…………………………………………………………………iv一章 緒論.1 概述………………………………………………………………… 1.2 文獻回顧…………………………………………………………… 2.3 章節簡介…………………………………………………………… 6二章 圓極化天線機制.1 天線極化介紹……………………………………………………… 7.2 傳統圓極化天線介紹……………………………………………… 9.3 序列式旋轉饋入公式推導…………………………………………11三章 序列式旋轉之饋入電路設計.1設計原理及方法…………………………………………………… 15.2實驗驗證…………………………………………………………… 17.3結論………………………………………………………………… 25四章 適用於序列式旋轉方法之天線設計.1概述………………………………………………………………… 29.2天線元件設計與實驗驗證證……………………………………… 32.3天線元件參數分析與輻射機制探討……………………………… 39.4結論………………………………………………………………… 47五章 寬頻序列式旋轉天線陣列.1序列式旋轉 天線陣列………………………………………………49.2使用本論文設計饋入電路一之 天線陣列…………………………57.3使用本論文設計饋入電路二之 天線陣列…………………………64.4結論………………………………………………………………… 70六章 總結…………………………………………………………… 73考文獻…………………………………………………………………7
Theoretical Study of Singlet Fission in Polyacene Dimers
No full text單重態激發子分裂，一個經由吸收單一光子產生兩個獨立三重態激
發子的光化學現象，由於具有應用於高效能太陽能發電材料的潛力而
備受囑目。然而，儘管大量的研究資源投入於此領域之中，科學家們
對於單重態激發子分裂的反應機制依然沒有達成共識，並且尚存在著
許多未解決的疑問。例如：驅使單重態激發子分裂發生的因素為何，
以及當中牽涉到的激發態波函數真正的性質等等。
從電子結構的觀點著手，我們利用非絕熱基底近似成功地展示了激發
態中電子躍遷圖像，以及利用有限電子活躍空間的電子組態交互作用
（考慮單電子及雙電子激發）計算闡述了多重組態效應在多並苯的電子
結構中扮演著相當重要的角色，尤其是來自雙重單重態電子組態的影
響。
藉由建立弗朗凱爾激發態-電荷轉移態-雙重單重態的三能態模型，我
們成功地解釋實驗上觀測到在飛秒尺度下發生的單重態激發子分裂，
並說明了其是藉由強烈的超交換耦合常數以及近乎重能態的條件而發
生的。我們發現到在影響單重態激發子分裂的因素之中，電荷轉移能
態的能階位置大幅地影響著超交換耦合常數的數值，因此被認為是最
重要的因素。因此，除了過去考慮第一單重態與兩倍三重態之能量差
以外，我們提出電子轉移態能階的降低應該也要納入判斷單重態激發
子分裂發生與否的考量之中。
另外，藉由從分子軌域對電子組態交互作用的分析，我們可以從單分
子的分子軌蜮來瞭解二重體中兩個分子的相對位置會對單重態激發子
分裂帶來什麼樣的影響。此方法不但能省去電子組態交互作用昂貴的
計算資源而提供對電子結構定性的分析，也能進而從分子設計的觀點
去提出發生高效率單重態激發子分裂的分子設計方向。Because of the promising potential in the high efficiency solar cell, singlet exciton fission, the molecular analogue of multiexciton generation resulting in two independent triplet excitons by absorbing a single photon, has attracted
increasing attention recently. Although the striking research works are advancing, the mechanism of SF is still controversial, and some open questions remain, e.g., the key parameters manipulating the occurrence of SF and the excited state wavefunctions involved in it. From an electronic structure point of view, we construct an approximate diabatic basis to unambiguously interpret the character of the excited states, by applying the restricted active space
configuration interaction single and double approach to show the importance of considering multi-configuration effects in polyacene dimers, especially the key role of double-excitation configurations. Using a three-state model, strong superexchange effective coupling and the near degeneracy condition that explain the ultrafast SF mechanism are obtained. We demonstrate that a crucial factor is the energetic position of the charge transferred diabatic state,
which remarkably controls the amplitude of the effective coupling. Therefore, in addition to the near degeneracy of the lowest lying singlet exciton and the double-triplet state, we conclude that the lowering of the charge transferred diabatic state energy should also be considered as a key factor for the design of hign efficiency SF materials. Finally we show that dominant interactions
controlling SF efficiency in a dimer can be decomposed into Conlomb interaction between monomer molecular orbitals. Trough molecular orbital based analysis of configuration interactions involved in the SF process, the driving
force of SF can be determined from the relative orientation of monomers, providing an effective method to survey potential molecules and further guideline to the design principle of high SF dye-sensitizing materials.口試委員會審定書 i
致謝ii
中文摘要iv
Abstract v
Contents vii
List of Figures x
List of Tables xiii
1 Introduction 2
1.1 Singlet Fission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Experimental Development . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Theoretical Development . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 Method 10
2.1 Oligoacene Model Systems . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 Hartree-Fock Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3 Localization of Molecular Orbitals . . . . . . . . . . . . . . . . . . . . . 11
2.4 Restricted Active Space Configuration Interaction Single and Double (RASCISD)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
vii
3 Semi-empirical Calculation 19
3.1 Pariser–Parr–Pople (PPP) Model . . . . . . . . . . . . . . . . . . . . . . 19
3.2 Electronic Structure of Pentacene Dimer . . . . . . . . . . . . . . . . . . 20
3.3 Dependence of the Electronic Structure on the Face-to-face Distance . . . 22
3.4 Electronic Structure Dependence on Molecular Size . . . . . . . . . . . . 22
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4 ab initio Study of SF in Pentacene Dimer 25
4.1 Direct Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2 RAS-CISD Low-lying Electronic Excitations . . . . . . . . . . . . . . . 26
4.3 Three-state Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.4 Size of Active Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5 Singlet Fission in Oligoacene Series 34
5.1 RAS-CISD Calculation of Anthracene & Tetracene Dimers . . . . . . . . 34
5.2 Effective SF Hamiltonian for oligoacene Dimers . . . . . . . . . . . . . . 37
5.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6 Dependence of Electronic Structure on Geometrical Effect 41
6.1 Molecular Structure Effect . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.2 Effective SF Coupling Dependence on the Geometrical Effect . . . . . . 45
6.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7 Molecular Orbital Perspective on Effective SF Coupling 47
7.1 Estimation of Effective SF Coupling . . . . . . . . . . . . . . . . . . . . 47
7.2 Electronic Coupling from MO Interactions . . . . . . . . . . . . . . . . 50
7.3 State Energy from MO Interactions . . . . . . . . . . . . . . . . . . . . . 56
7.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
8 Conclusion 58
viii
A Appendix 61
A.1 Visualization of Localized MOs . . . . . . . . . . . . . . . . . . . . . . 61
Bibliography 6
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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