表面等離子體激元和熒光分子之間的電磁相互作用已因廣泛應用於量子運算中的量子信息處理和分子生物技術的分子檢測而得到相當大的關注。雖然通過把熒光分子放置在電漿系統旁來改善熒光分子的發光度和方向性已被廣泛接受，但是了解表面等離子體激元和熒光材料之間的相互作用的物理亦是很重要的。 / 在這篇論文中，我們將研究在二維納米銀洞陣列上有機染料帶方向性的發光特性。通過量度在每個角度的反射和熒光發光光譜，我們可以繪製出二維納米銀洞陣列所產生的電磁共振模式的色散關係及熒光材料發光度與方向的關係。此外，在陣列上以不同方向行走的表面等離子體激元的衰變壽命亦被找出。我們亦將反射率和熒光發光光譜進行比較，從而發現熒光發光的加強跟表面等離子體激元的光譜位置、衰變後傳播的方向、它的衰變壽命和它的耦合效率有十分密切的關係。為了解背後的物理，我們建立了一個理論模型去區分能量從有機染料轉移到表面等離子體激元的過程與表面等離子體激元衰變過程對表面等離子體激元改變熒光材料發光度的影響。因此，我們可以對能量從有機染料轉移到表面等離子體激元的過程與方向的關係進行定量分析。最後，我們的研究結果與由有限差分時域模擬計算所得的結果吻合。結論得出在二維納米銀洞陣列上所實現的表面等離子體激元増加有機染料光提取效率與三維空間中方向的關係是源於電漿帶隙的產生所引致的態密度重整及分配。 / The electromagnetic interaction between surface plasmon polaritons (SPPs) and fluorescent molecules has been capturing considerable attention for a wide variety of applications ranging from quantum information processing in quantum computing to molecule detection in biotechnology. Although it is widely accepted that the light emission efficiency and directionality are improved by placing the fluorescent molecules in close proximity to a plasmonic system, the understanding of the physics on how SPPs interact with the fluorescent materials is of importance. / In this thesis, the directional emission properties of LDS organic dyes supported on two-dimensional Ag nanohole array is studied. Angle-resolved reflectivity and photoluminescence spectroscopy have been employed to map out the dispersion relations of electromagnetic resonance modes arising from the array and the dependence of plasmonic emission on emission angle. In addition, the decay lifetimes of SPP modes in different propagation directions in array have been determined. By comparing the reflectivity and photoluminescence mappings, we find that the emission enhancement is strongly correlated with the spectral and angular positions of SPP modes together with their lifetimes and coupling efficiencies. To understand the underlying physics, we have developed an analytical model to differentiate the surface plasmon mediated emission (SPME) into energy transfer from LDS to SPPs and the radiative decay of surface plasmons. As a result, the directional dependence of the energy transfer process can then be analyzed quantitatively. Finally, our results are compared with the finite-difference-time-domain simulations with good agreement. It is concluded that the directional dependence of the surface plasmon mediated emission is attributed to the redistribution of the density of states in the periodic nanohole array due to the opening of the plasmonic gaps. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Chan, Kay Fung = 表面等離子體激元改變納米金屬洞陣列上發光材料的光提取效率 / 陳其鋒. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 115-123). / Abstracts also in Chinese. / Chan, Kay Fung = Biao mian deng li zi ti ji yuan gai bian na mi jin shu dong zhen lie shang fa guang cai liao de guang ti qu xiao lu / Chen Qifeng. / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Surface plasmon polaritons (SPPs) and surface plasmon mediated emission (SPME) --- p.2 / Chapter 1.2 --- Directional surface plasmon mediated emission (SPME) on metallic nanohole array --- p.5 / Chapter 1.3 --- Our analytical model of surface plasmon mediated emission --- p.8 / Chapter 1.3.1 --- Formalism of rate equations --- p.8 / Chapter 1.3.2 --- Determination of the directional dependence of the coupling efficiency from decay rates of the SPP and the fluorescent material --- p.11 / Chapter 1.4 --- Organization of the thesis --- p.12 / Chapter Chapter 2 --- Theory of surface plasmon polaritons --- p.14 / Chapter 2.1 --- The Maxwell’s equations and the boundary conditions for electromagnetic waves --- p.14 / Chapter 2.2 --- Dielectric constant of metal --- p.18 / Chapter 2.3 --- Master equation for electromagnetic waves, the Bloch form of SPPs and the dispersion relation of SPPs at the interface between dielectric and metal --- p.19 / Chapter 2.4 --- Excitation of surface plasmon polaritons by grating coupling --- p.27 / Chapter 2.5 --- Decay of surface plasmon polaritons --- p.29 / Chapter 2.5.1 --- Non-radiative decay --- p.29 / Chapter 2.5.2 --- Radiative decay --- p.31 / Chapter Chapter 3 --- Experimentation and Simulation --- p.37 / Chapter 3.1 --- Sample preparation --- p.37 / Chapter 3.1.1 --- Interference lithography [2.2, 3.7, 3.8] --- p.37 / Chapter 3.1.2 --- E-beam evaporation --- p.39 / Chapter 3.1.3 --- Spin coating of florescence material --- p.40 / Chapter 3.2 --- Measurements --- p.41 / Chapter 3.2.1 --- Angle-resolved specular reflection measurement [3.10] --- p.42 / Chapter 3.2.2 --- Angle-resolved photoluminescence (PL) spectroscopy [3.11] --- p.43 / Chapter 3.2.3 --- K-space (Fourier space) imaging [3.12, 3.13, 3.14] --- p.44 / Chapter 3.3 --- FDTD --- p.46 / Chapter 3.3.1 --- Theory of FDTD --- p.46 / Chapter 3.3.2 --- Simulation of the reflectivity of plane wave --- p.52 / Chapter 3.3.3 --- Simulation of the field pattern with a dipole source --- p.55 / Chapter 3.3.3.1 --- Near-to-far field projection --- p.59 / Chapter 3.3.3.2 --- Near field pattern in k-space --- p.60 / Chapter Chapter 4 --- Analysis --- p.62 / Chapter 4.1 --- Angle-resolved reflectivity measurement --- p.62 / Chapter 4.1.1 --- SPP mode identification --- p.62 / Chapter 4.1.2 --- Wavelength dependence of uncoupled SPPs decay rates --- p.65 / Chapter 4.1.3 --- Directional dependence of uncoupled SPPs decay rates --- p.71 / Chapter 4.2 --- Angle-resolved PL spectroscopy --- p.79 / Chapter 4.2.1 --- Comparison with the angle-resolved reflectivity --- p.79 / Chapter 4.2.2 --- Differentiation of the resonance and off-resonance positions on the PL mapping --- p.81 / Chapter 4.3 --- K-space imaging --- p.83 / Chapter 4.3.1 --- Reflectivity and the comparison with the phase - matching equation --- p.83 / Chapter 4.3.2 --- k-space imaging of the PL emission --- p.85 / Chapter 4.4 --- Directional dependence of the emission factor --- p.86 / Chapter 4.5 --- Directional dependence of the coupling rate of the LDS emission to the SPP mode --- p.94 / Chapter 4.6 --- Near field in k-space from the FDTD method --- p.97 / Chapter Chapter 5 --- Conclusions --- p.113 / Bibliography --- p.115

Since its physical isolation via the "scotch tape method," graphene (a monolayer of graphite) has attracted much attention from both the solid-state and high-energy scientific communities because its elementary excitations mimic relativistic chiral fermions. This has allowed graphene to act as a testbed for exploring exotic forms of symmetry breaking and for verifying certain longstanding theoretical predictions dating back to the very first formulation of relativistic quantum mechanics. In this dissertation I describe scanning tunneling microscopy and spectroscopy experiments that visualize ordered electronic states in graphene that originate from its unique chiral structure. Two detailed investigations of chemical vapor deposition graphene grown on copper are presented. In the first, a heretofore unrealized phase of graphene with broken chiral symmetry called the Kekulé distortion is directly visualized. In this phase, the graphene bond symmetry breaks and manifests as a (√3×√3)R30° charge density wave. I show that its origin lies in the interactions between individual vacancies ("ghost adatoms") in the crystalline copper substrate that are mediated electronically by the graphene. These interactions induce the formation of a hidden order in the positions of the ghost adatoms that coincides with Kekulé bond order in the graphene itself. I then show that the transition temperature for this ordering is 300K, suggesting that Kekulé ordering occurs via enhanced vacancy diffusion at high temperature. In the second, Klein tunneling of electrons is visualized for the first time. Here, quasi-circular regions of the copper substrate underneath graphene act as potential barriers that can scatter and transmit electrons. At certain energies, the relativistic chiral fermions in graphene that Klein scatter from these barriers are shown to fulfill resonance conditions such that the transmitted electrons become trapped and form standing waves. These resonant modes are visualized with detailed spectroscopic images with atomic resolution that agree well with theoretical calculations. The trapping time is shown to depend critically on the angular momenta quantum number of the resonant state and the radius of the trapping potential, with smaller radii displaying the weakest trapping.

Atomically thin two-dimensional materials, such as graphene and semiconductor transition metal dichalcogenides (TMDCs), exhibit remarkable and desirable optical and electronic properties. This dissertation focuses on the excitonic properties of monolayer TMDCs taken first in isolation and then in contact with another material. We begin with a study of the exciton binding energy in two monolayer TMDCs, WS₂ and MoS₂. We observe excited states of the exciton by two different optical spectroscopy techniques: reflectance contrast and photoluminescence excitation (PLE) spectroscopy. We fit a hydrogenic model to the energies associated with the excited states and infer a binding energy, which is an order of magnitude higher than the bulk material. In the second half of this work, we study two types of two-dimensional vertical heterostructures. First, we investigate heterostructures composed of monolayer WS₂ partially capped with graphene one to four layers thick. Using reflectance contrast to measure the spectral broadening of the excitonic features, we measure the decrease in the coherence lifetime of the exciton in WS₂ due to charge and energy transfer when in contact with graphene. We then compare our results with the exciton lifetime in MoS₂/WS₂ and MoSe₂/WSe₂ heterostructures. In TMDC/TMDC heterostructures, the decrease in exciton lifetime is twice that in WS₂/graphene heterostructures and due predominantly to charge transfer between the layers. Finally, we probe the band alignment in MoS₂/WS₂ heterostructures using scanning tunneling microscopy (STM) and spectroscopy (STS).We confirm the monolayer band gaps and the predicted type II band alignment in the heterostructure. Drawing from all the research presented, we arrive at a favorable conclusion about the viability of TMDC based devices.

Nanoscale structural characterization is critical to understanding the physical underpinnings of properties and behavior in materials with technological applications. The work herein shows how the pair distribution function technique can be applied to x-ray total scattering data for material systems which weakly scatter x-rays, a typically difficult task due to the poor signal-to-noise obtained from the structures of interest. Characterization and structural modeling are demonstrated for a variety of molecular and porous systems, along with the detection and characterization of disordered, minority phases and components. In particular, reliable detection and quantitative analysis are demonstrated for nanocrystals of an active pharmaceutical ingredient suspended in dilute solution down to a concentration of 0.25 wt. %, giving a practical limit of detection for ordered nanoscale phases within a disordered matrix. Further work shows that minority nanocrystalline phases can be detected, fingerprinted, and modeled for mixed crystalline and amorphous systems of small molecules and polymers. The crystallization of amorphous lactose is followed under accelerated aging conditions. Melt quenching is shown to produce a different local structure than spray drying or freeze drying, along with increased resistance to crystallization. The initial phases which form in the spray dried formulation are identified as a mixture of polymorphs different from the final α-lactose monohydrate form. Hard domain formation in thermoplastic polyurethanes is also characterized as a function of methylene diphenyl diisocyanate and butanediol component ratio, showing that distinct and different hard phase structures can form and are solved by indexing with structures derived from molecular dynamics relaxation. In both cases, phase fractions can be quantified in the mixed crystalline and amorphous systems by fitting with both standards or structure models. Later chapters, demonstrate pair distribution characterization of particle incorporation, structure, and synthesis of nanoporous materials. Nanoparticle size distributions are extracted from platinum nanoparticles nucleating within a zeolite matrix through structural modeling, and validated by transmission electron microscope studies. The structure of zirconium phosphonate-phosphate unconventional metal organic framework is determined to consist of turbostratically disordered nanocrystalline layers of Zr-phenylphosphonate, and the local environment of terbium intercalated between the layers is found to resemble the local environment in scheelite-type terbium phosphate. Finally, the early stages of reaction between aqueous zinc dinitrate hexahydrate and methanolic 2-methylimidazole are characterized using in situ total scattering measurements, showing that secondary building units of tetrahedrally coordinated by 2-methylimidazole initially form upon reaction. Overall, the methodologies are developed and applied toward phase detection, identification, solution, and behavior in pharmaceuticals, polymers, and nanoporous materials along with advice for carrying out experiments and analysis on such materials such that they can be extended to other similar systems.

Since the successful isolation of graphene in 2004, two-dimensional (2D) materials have become one of the hottest research fields in material science. My research is about two kinds of popular 2D materials--graphene and transition metal dichalcogenides (TMDCs). Making graphene into nanoribbons has been predicted and demonstrated to be an effective way to open a bandgap in this pristinely zero-bandgap 2D material. But the rough edge condition of etched graphene nanoribbons has always been a big issue adversely affecting electron transport performance. The electron mean free path of this kind of devices is usually way below the channel width. By using a dual-gate structure based on bilayer graphene/hexagonal boron nitride heterostructure, we found a way to form 300nm-wide conducting channels with high aspect ratio (>15) that can achieve ballistic transport, indicating perfect edge conditions. As the first star member of TMDCs family, monolayer MoS2 is predicted to be strongly piezoelectric, an effect that disappears in the bulk owing to the opposite orientations of adjacent atomic layers. We conduct the first experimental study of the piezoelectric properties of two-dimensional MoS2 and show that cyclic stretching and releasing of thin MoS2 flakes with an odd number of atomic layers produces oscillating piezoelectric voltage and current outputs, whereas no output is observed for flakes with an even number of layers. In agreement with theoretical predictions, the output increases with decreasing thickness and reverses sign when the strain direction is rotated by 90 degrees. Transport measurements show a strong piezotronic effect in single-layer MoS2, but not in bilayer and bulk MoS2. Monolayer WSe2, another popular TMDC, has also attracted much recent attention. In contrast to the initial understanding, the minima of the conduction band are predicted to be spin split. Because of this splitting and the spin-polarized character of the valence bands, the lowest-lying excitonic states in WSe2 are expected to be spin-forbidden and optically dark. We show how an in-plane magnetic field can brighten the dark excitonic states and allow their properties to be revealed experimentally in monolayer WSe2. In particular, precise energy levels for both the neutral and charged dark excitons were obtained. Greatly increased emission and valley lifetimes were observed for the brightened dark states as a result of their spin configuration.

This thesis describes methods for constructing nanopatterned surfaces to array DNA. These surfaces enable direct observation of heretofore-unseen single-molecule reactions, eliminating bulk effects and enabling scientists to examine DNA mismatch repair and replication, including the first direct visualization of proteins binding to a target mismatch. This also facilitates directed self-organization of nanoscale features on a patterned substrate using DNA as an assembly tool. To make techniques for single-molecule visualization of biological processes more accessible, we have developed a novel technology called "DNA curtains," in which a combination of fluid lipid bilayers, nanofabricated barriers to lipid diffusion, and hydrodynamic flow can organize lipid-tethered DNA molecules into dened patterns on the surface of a microfluidic sample chamber. Using DNA curtains, aligned DNA molecules can be visualized by total internal reflection fluorescence microscopy, allowing simultaneous observation of hundreds of individual molecules within a field-of-view. Ultimately, this results in a 100X improvement in experimental throughput, and a corresponding increase in statistically signicant amounts of data. We also demonstrate site-specific labeling of DNA using DNA analogues, such as peptide nucleic acid (PNA), locked nucleic acid (LNA), and techniques such as nick-translation. Through PNA invasion, labeled DNA was self-assembled in arrays on surfaces and tagged with gold nanoparticles. In this work, DNA formed a template to self-assemble a nanoparticle in between nanoimprinted AuPd dots. Surface-based self-assembly methods offer potential for DNA employment in bottom-up construction of nanoscale arrays. This offers further proof that DNA can be useful in directed self-assembly of nanoscale architectures.

Superatomic crystals (SACs) with tunable physical properties offer a new approach to the design of inorganic nanomaterials. Very little is known about how these systems function, or how their properties can be transformed. Here I describe work that helps to develop an understanding of how functional properties behave in SACs, and how they can be altered through superatomic intercalation or with phase transitions. Chapter 1 describes work characterizing the thermal transport behavior of SACs. We find that heat transfer is dominated by coherent inter-cluster phonons with vibrational frequencies determined by the periodicity of the SAC superstructure. We also demonstrate a transformation from amorphous to crystalline thermal transport behavior through manipulation of the vibrational landscape and orientational order of the superatoms. Chapters 2 and 3 describe the intercalation of a porous superatomic host, [Co6Te8(PnPr3)6][C60]3. We find that guests can be inserted into the superstructure through single-crystal-to-single-crystal transformations, dramatically transforming the electronic properties of the SAC. Using electronic absorption spectroscopy, electrical transport measurements and electronic structure calculations, we demonstrate that the intercalation is driven by the exchange of charge between the host, establishing an exciting design space for the preparation of superatomic materials. Chapter 4 describes a hierarchical solid, [Co6Te8(PEt3)6][C70]2, in which the delicate balance of interactions between constituent building blocks produces two separate phase transitions: one affecting thermal transport properties, the other transforming the electronic and magnetic behavior of the SAC. We use a wide range of structural and spectroscopic characterization tools to understand the mechanism of each transformation. This work establishes a new ability to program functional phase transitions into cluster-assembled materials. In a completely different area of study, chapter 5 describes a new covalent organic framework (COF) whose unique structure enables a post-synthetic topochemical polymerization of the framework’s linker fragments. The polymerization of the 1-3 butadiyne into a polydiacetylene backbone covalently crosslinks the material without compromising its original crystallinity. This work not only enables the preparation of more structurally resilient COFs, but also diversifies the design space for this emerging class of materials.

Two dimensional (2D) materials have unique properties that make them exciting candidates for various optical and electronic applications. Materials such as graphene and transition metal dichalcogenides (TMDCs) have been intensively studied recently with researchers racing to show advances in 2D device performance while developing a better understanding of the material properties. Despite recent advances,there are still significant roadblocks facing the use of 2D materials for real-world applications. The ability to make reliable, low-resistance electrical contact to TMDCs such as molybdeum disulfide (MoS22) has been a challenge that many researchers have sought to overcome with novel solutions. The work laid out in this dissertation uses novel techniques for addressing these issues through the use of improved device fabrication and with a clean, and potentially scalable doping method to tune 2D material properties.A high-performance field-effect transistor (FET) was fabricated using a new device platform that combined graphene leads with dielectric encapsulation leading to the highest reported value for electron mobility in MoS2. Device fabrication techniques were also investigated and a new, commercially available lithography tool (NanoFrazor) was used to pattern contacts directly onto monolayer MoS2. Through a series of control experiments with conventional lithography, a clear improvement in contact resistance was observed with the use of the NanoFrazor. Plasma-doping, a dry and clean process, was investigated as an alternative to traditional wet-chemistry doping techniques. In addition to developing doping parameters with a chlorine plasma treatment of graphene, a series of experiments on doped graphene were conducted to study its effect on optical properties. Whereas previous studies used electrostatic gating to modify graphene’s optical properties, this work with plasma-doped graphene showed the ability to tune absorbence and plasmon wavelength without the need for an applied bias opening the door to the potential for low-power applications. This work is a just small contribution to the larger body of research in this field but hopefully represents a meaningful step towards a greater understanding of 2D materials and the realization of functional applications.

No description available.

Leung Yee Pan = 利用有機金屬化學氣相沉積方法生長一維硒化鋅鈉米結構 / 梁懿斌. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 80-82). / Text in English; abstracts in English and Chinese. / Leung Yee Pan = li yong you ji jin shu hua xue qi xiang chen ji fang fa sheng chang yi wei xi hua xin na mi jie gou / Liang Yibin. / Acknowledgements --- p.ii / Abstract --- p.iii / Chapter Chapter 1 - --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Motivation --- p.3 / Chapter 1.2.1 --- ZnSe --- p.3 / Chapter 1.2.2 --- MOCVD --- p.3 / Chapter 1.3 --- Our Work --- p.4 / Chapter Chapter 2 - --- Experiment --- p.5 / Chapter 2.1 --- MOCVD System --- p.5 / Chapter 2.2 --- Metalorganic Sources --- p.5 / Chapter 2.3 --- Substrates --- p.7 / Chapter 2.4 --- Substrate Preparations --- p.7 / Chapter 2.5 --- Preheating (Applied Only when Using GaAs Substrates) --- p.7 / Chapter 2.6 --- Growth of Epi-layer (Applied Only when Using GaAs Substrates) --- p.8 / Chapter 2.7 --- Growth of ZnSe Nanowires on Si(100) and ZnSe/GaAs(100) --- p.8 / Chapter 2.8 --- The Samples --- p.9 / Chapter Chapter 3 - --- Characterization --- p.10 / Chapter 3.1 --- Surface Morphologies --- p.10 / Chapter 3.1.1 --- Scanning Electron Microscopy --- p.10 / Chapter 3.1.2 --- Atomic Force Microscopy --- p.12 / Chapter 3.2 --- Structural Properties - X-Ray Diffraction --- p.13 / Chapter 3.3 --- Optical Properties - Photoluminescence --- p.15 / Chapter 3.4 --- Other Techniques --- p.16 / Chapter Chapter 4 - --- Results --- p.17 / Chapter 4.1 --- ZnSe Nanowires Grown on Si(100) --- p.17 / Chapter 4.1.1 --- Effect of Growth Temperature --- p.17 / Chapter 4.2 --- Growth of ZnSe Nanowires on GaAs( 100) - The First Trial --- p.20 / Chapter 4.3 --- Optimizing the ZnSe Epi-layer --- p.21 / Chapter 4.3.1 --- Surface of GaAs(100) --- p.21 / Chapter 4.3.2 --- ZnSe Epi-layer Grown at Different Reactor Pressures --- p.22 / Chapter 4.4 --- Importance of Au --- p.26 / Chapter 4.5 --- Growth of ZnSe Nanowires on GaAs(lOO) - A Systematic Study --- p.28 / Chapter 4.5.1 --- Growth Rates --- p.28 / Chapter 4.5.2 --- Overall Morphologies --- p.32 / Chapter 4.5.3 --- Classifying the Morphologies --- p.37 / Chapter 4.5.4 --- Abundances of Different Morphologies of Different Samples --- p.40 / Chapter 4.5.5 --- Growth Direction --- p.45 / Chapter 4.5.6 --- Structure of the Nanowires --- p.50 / Chapter 4.5.7 --- Optical Properties of the Nanowires --- p.54 / Chapter Chapter 5 - --- Discussions --- p.57 / Chapter 5.1 --- Overview of the MOCVD Process --- p.57 / Chapter 5.1.1 --- Effects of Growth Temperature on Growth Rate of MOCVD --- p.58 / Chapter 5.1.2 --- Effects of Reactor Pressure on Growth Rate of MOCVD --- p.59 / Chapter 5.2 --- Effect of Reactor Pressure on the Growth Rate of the Nanowires --- p.60 / Chapter 5.3 --- Growth Mechanisms of the Nanowires --- p.64 / Chapter 5.3.1 --- VLS Mechanism --- p.64 / Chapter 5.3.2 --- Spiral Growth Mechanism --- p.66 / Chapter 5.3.3 --- Reentrant Corner Mechanism --- p.67 / Chapter 5.3.4 --- Roles of Au Particles and ZnSe Epi-layer --- p.68 / Chapter 5.3.5 --- Growth Mechanisms of Different Types of Nanowires --- p.69 / Chapter 5.3.6 --- Effect of Growth Temperature --- p.71 / Chapter 5.4 --- Quality of the Nanowires --- p.72 / Chapter 5.5 --- "Remarks of the AFM Experiments and the ""Transferred"" Samples" --- p.72 / Chapter Chapter 6 - --- Conclusions --- p.75 / Appendices --- p.77 / Chapter I - --- "Estimation of the mass, other than the nanowires, contributed to the sample" --- p.77 / Chapter II - --- Calculation of the growth angle with respect to the surface normal --- p.78 / References --- p.80