This thesis is a continuous effort contributed to the field of developing a new type of functional porous materials - Nanocarbon Foam (NCF) by crosslinking multi-walled carbon nanotubes (MWNTs) into networks in three-dimensional (3D). Synthetic routes and characterizations of NCF, and their applications as strain-gauge sensors and electrode materials in lithium-air (Li-air) battery are described. In this research, the first accomplishment is proposing a robust methodology for creating superealstic 3D macroscopic NCF with controlled cellular structure. The key contributions contain: (1) understanding the premise of the design that gives the NCF with desired structure and porosity; (2) designing fabrication protocol for NCFs with controlled densities and macroscopic structure; (3) fabricating varied NCF with tunable porosity and structures, which in turn will endow the NCF with different characteristics. This experimental methodology for systematic and quantitative investigation of the processing-structure relationships provides a means for the fabrication optimization of NCF with desired structures. Though the mechanical, electronic, and thermal properties of CNTs have been extensively studied, for NCF that is a mixture of pristine and functionalized CNTs, it will not only have the collective behavior of the individual tubes, but will also have properties generated from the interactions between the tubes and engineered components. To understand the structure-properties relationship of NCF, the second accomplishment is studying the properties of obtained NCFs. Density, specific surface area, porosity, compressive behavior, mechanical robustness, electrical and electromechanical properties of NCF have been characterized in details. For comparison, properties originated from cellular structures built of other materials, such as polymeric foam, fiber aerogels, etc., are compared with that of NCF. Moreover, some engineering applications of NCF have been discussed. With the unique features of NCFs, my proposed future work will focus on understanding porous structure formation and resulted unique properties by the means of scientific modelling. In addition, NCF will be explored as the skeleton for fabricating hybrid systems. / A Thesis submitted to the Materials Science and Engineering Program in partial fulfillment of the Master of Science. / Fall Semester 2015. / November 5, 2015. / Includes bibliographical references. / Eric Hellstrom, Professor Co-Directing Thesis; Mei Zhang, Professor Co-Directing Thesis; Richard Liang, Committee Member; Zhibin Yu, Committee Member.

Enhancing the beam energy of particle accelerators like the Large Hadron Collider (LHC), at CERN, can increase our probability of finding new fundamental particles of matter beyond those predicted by the standard model. Such discoveries could improve our understanding of the birth of universe, the universe itself, and/or many other mysteries of matter—that have been unresolved for decades—such as dark matter and dark energy. This is obviously a very exciting field of research, and therefore a worldwide collaboration (of universities, laboratories, and the industry) is attempting to increase the beam energy in the LHC. One of the most challenging requirements for an energy increase is the production of a magnetic field homogeneous enough and strong enough to bend the high energy particle beam to keep it inside the accelerating ring. In the current LHC design, these beam bending magnets are made of Nb-Ti superconductors, reaching peak fields of ~8 T. However, in order to move to higher fields, future magnets will have to use different and more advanced superconducting materials. Among the most viable superconductor wire technologies for future particle accelerator magnets is Nb₃Sn, a technology that has been used in high field magnets for many decades. However, Nb₃Sn magnet fabrication has an important challenge: the fact the wire fabrication and the coil assembly itself must be done using ductile metallic components (Nb, Sn, and Cu) before the superconducting compound (Nb₃Sn) is activated inside the wires through a heat treatment. The studies presented in this thesis work have found that the heat treatment schedule used on the most advanced Nb₃Sn wire technology (the Restacked Rod Process wires, RRP®) can still undergo significant improvements. These improvements have already led to an increase of the figure of merit of these wires (critical current density) by 28%. / A Dissertation submitted to the Program in Materials Science and Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2017. / April 11, 2017. / image anaylsis, LHC, magnets, Nb3Sn, RRP, superconductivity / Includes bibliographical references. / David Larbalestier, Professor Directing Dissertation; Vincent Salters, University Representative; William Oates, Committee Member; Michael Shatruk, Committee Member; Irinel Chiorescu, Committee Member; Chiara Tarantini, Committee Member; Peter Lee, Committee Member.

My research has been focusing on the development and processing of metal halide perovskites, an emerging class of semiconductor materials, for various types of light emitting diodes (LEDs). In this dissertation, introduction to metal halide perovskites will be presented in the chapter 1, followed by three chapters detailing the work on the use of metal halide perovskites as hole transport layer for organic LEDs (chapter 2), as light emitting layer for electrically driven LEDs (chapter 3), and down conversion LEDs (chapter 4). A new type of hole transport layer based on metal halide perovskite, CH3NH3PbCl3 has been demonstrated for highly efficient OLEDs. Two types of hole transport layer have been fabricated, including PIP-CH3NH3PbCl3 composite thin films and neat CH3NH3PbCl3 thin films. Solution processed multilayer green phosphorescent OLEDs based on this new PIP- CH3NH3PbCl3 nanograss HTLshowed superior performance over devices using conventional PEDOT: PSS HTL with lower turn-on and operating voltages, as well as higher brightness. The improved device performance is primarily attributed to the high conductivity of CH3NH3PbCl3 and large interpenetrating interfaces between the hole transporting perovskite nanopillars and the emitting layer. In order to further enhance efficiencies of OLEDs based on CH3NH3PbCl3 as HTL, the solvent passivation approach has been adapted for the formation of smooth neat CH3NH3PbCl3 perovskite thin films with great surface coverage. Solution-processed multilayer green phosphorescent OLEDs based on this new perovskite HTL showed superior performance over the device using conventional PEDOT:PSS HTL, with lower turn-on and operating voltages, as well as higher brightness, EQE, power efficiency and luminous efficiency. The improved device performance is primarily attributed to the wide band gap of CH3NH3PbCl3, suitable energy levels, and efficient the hole injection and transport from ITO to CH3NH3PbCl3 and light emitting layer. This work demonstrates a new pathway toward highly efficient solution processed multilayer OLEDs, and further establishes organic-inorganic halide perovskites as a new class of semiconductors with highly desirable characteristics for thin film optoelectronic devices. Perovskite LEDs have recently attracted great research interest for their narrow emissions and solution processability. Remarkable progress has been achieved in green emitting perovskite LEDs in recent years, but not blue or red ones. Highly efficient and spectrally stable red perovskite LEDs with quasi-2D perovskite/poly (ethylene oxide) (PEO) composite thin films as the light-emitting layer have been successfully demonstrated. By controlling the molar ratios of organic salt (benzyl ammonium iodide) to inorganic salts (cesium iodide and lead iodide), luminescent quasi-2D perovskite thin films are obtained with tunable emission colors from red to deep red. The perovskite/polymer composite approach enables quasi-2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi-2D perovskite counterparts. Electrically driven LEDs with emissions peaked at 638, 664, 680, and 690 nm have been fabricated to exhibit high brightness and external quantum efficiencies (EQEs). For instance, the perovskite LED with an emission peaked at 680 nm exhibits a brightness of 1392 cd/m2 and an EQE of 6.23%. Both the maxima brightness and external quantum efficiencies of our devices are among the highest reported to date for red perovskite LEDs. Moreover, exceptional electroluminescence spectral stability under continuous device operation has been achieved for these red perovskite LEDs. This work clearly shows the effectiveness of processing and device engineering to realize high performance perovskite optoelectronic devices. Recently, our lab developed a new class of luminescent materials, zero-dimensional perovskites. These novel luminescent materials show very high photoluminescence quantum efficiencies (PLQEs) with a very broad emission. For these new 0D perovskites, their excellent optical properties enable us to fabricate down conversion white LEDs. By combing these new 0D perovskites with commercialized blue phosphor, I have successfully fabricated down conversion white LEDs with high color quality. For example, a new type of mixed halide 0D perovskite, (C4N2H14Br)4SnBrxI6–x (x = 3), with a PL emission peak of 582 nm, a larger FWHM of 126 nm and a high PLQEs of 85% have been used as yellow phosphors in down conversion LEDs. By overcoming the issue of deficiency in the red emission present in most yellow phosphors, this 0D tin mixed-halide perovskite enabled optically pumped WLEDs with high color rendering index (CRIs) of up to 85. / A Dissertation submitted to the Program in Materials Science and Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2018. / April 20, 2018. / CH3NH3PbCl3, hole transport layer, light emitting diodes, OLEDs, perovskites, quasi-2D perovskites / Includes bibliographical references. / Biwu Ma, Professor Directing Dissertation; Peng Xiong, University Representative; Eric Hellstrom, Committee Member; Theo M. Siegrist, Committee Member; Chen Huang, Committee Member.

Self-assembled bilayers consisting of a monolayer of molecules, a metal linking ion and a second molecular layer were prepared and used in controlling critical energy and electron transfer events in dye-sensitized solar cells (DSSCs). DSSCs have shown promise as an alternative to traditional silicon solar cells due to their ease of fabrication and lower manufacturing costs. Despite the high efficiency to cost ratio, DSSCs face the limitations of detrimental recombination across the dye-semiconductor interface as well as narrow absorption transitions which respectively lower the open circuit voltage and short circuit current of these cells. Bilayers consisting of a bridging molecule, zirconium metal ion and N3 dye were assembled on a nanocrystalline metal oxide electrode as a means of inhibiting deleterious recombination processes in DSSCs. Bilayer formation was confirmed by ATR-IR and UV−vis spectroscopy. Interfacial electron transfer events in DSSCs were characterized by electrochemical and photophysical measurements. The results show an increased electron lifetime, diffusion length and open circuit voltage with increasing bridge length. The increased separation between the TiO2 and dye however also reduced injection rate, by extension, photocurrent and the overall efficiency of the DSSC devices. Self-assembled bilayer was also used to achieve broadband light harvesting in DSSCs by incorporating two complementary absorbing dyes. The bilayer here consisted of a monolayer of pN3 dye, zirconium metal ion and p1M dye. The UV-vis and ATR-IR absorption spectra of the bilayer were found to be the sum of the individual dyes. The bilayer devices also demonstrated about 10% higher photocurrent, voltage and power conversion efficiency over the monolayer DSSCs. This was attributed to slower recombination losses at the TiO2-dye1-dye2-electrolyte interfaces as well as higher photon-to-current conversion efficiency across the visible spectrum. A key factor towards the higher performance of the bilayer is directional energy and electron transfer from p1M to pN3 dye. Investigations into the role and properties of the metal ion when coordinated to a dye was further performed to understand how the nature of the metal ion influence the dynamics of the different processes at the dye-semiconductor interface. This can allow optimization of the bilayer architecture and enable its use for an even wider range of applications. 8 different metal ions were studied and coordination to the dye was confirmed by XPS, ATR-IR and UV-vis. Metal ion coordination had minimal influence on energetic levels of the dye with minimal shifts observed. Results suggest that electrostatic interactions between the metal ion and the iodide/triiodide species in the electrolyte as a primary determining factor in the rates of regeneration, back electron transfer and recombination processes as well as the photovoltaic parameters. A remarkable improvement of 130 mV was achieved with two of these metal ions. X-ray photoelectron spectroscopy was used to study the effect of zinc and zirconium metal ion treatment on the core binding energies of un-sensitized and sensitized TiO2 thin films. The metal treatment included treating the TiO2 film with metal ions without further treatment (TiO2 (Mn)) as well as prior to dye sensitization (TiO2 (Mn)-N3). Metal coordinated samples were also prepared (TiO2-N3-Mn). The results indicate there is no change in chemical state of the TiO2 but suggest that zinc treatment might have significant influence on the sulphur atom in the N3 dye. This interaction may also be a clue as to its perturbed diode behavior. / A Dissertation submitted to the Materials Science and Engineering Program in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2018. / April 13, 2018. / bilayer, dssc, electron transfer, recombination, self-assembled / Includes bibliographical references. / Kenneth Hanson, Professor Directing Dissertation; Simon Foo, University Representative; Hanwei Gao, Committee Member; Eric Hellstrom, Committee Member; Zhibin Yu, Committee Member.

Two Dimensional Materials has been the focus of much research in the past decade. We review 145 stable two dimensional materials in both bulk and monolayer. We compare their final electronic properties and discuss the results. Specifically, we discuss notable materials that have transitions between bulk and monolayer. Additionally, we use both the bulk and monolayer data to search for structural trends that may be corralated with the electronic properties using machine learning techniques. We find that our machine was able to produce results that predict the basic electronic properties with approximately 65% accuracy. / A Thesis submitted to the Program in Materials Science and Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2018. / July 17, 2018. / Monolayer, Two Dimensional Materials / Includes bibliographical references. / Jose Mendoza-Cortes, Professor Directing Thesis; Stratos Manousakis, Committee Member; Chen Huang, Committee Member.

University of Macau / Faculty of Science and Technology. / Department of Civil and Environmental Engineering

In the last decade, biological molecules such as Deoxyribonucleic acid (DNA) and some proteins have attracted attention as material candidates for molecular electronics applications. Yet, despite numerous studies of electron transport in DNA in particular, inconsistencies in experimental results persist. As a result, both the degree and mechanism of charge transport in these biological molecules remain disputed. To understand if different binding configurations of DNA on metal electrodes through unexpected moieties could be responsible for experimental inconsistencies in the literature, we investigate whether small molecules ubiquitous in both nucleic acids and amino acids, such as purines and imidazole, bind to gold electrodes and produce conductance signature. In this study, we use the Scanning Probe Microscope-based Break Junctions approach method to study single molecule conductance and binding geometry of the purine bases of DNA, particularly adenine and guanine. In addition, the Conductive Atomic Force Microscope-based Break Junction (CAFMBJ) platform has been created to simultaneously measure both electrical and mechanical properties of these single molecule junctions. Our measurements indicate that purines bind in the junction and display several robust conductance signatures on gold. We find that both purine and adenine bind through the imidazole, which is identified, for the first time, as a new linker group for single molecule conductance measurements.

REBCO (REBa2Cu3O7-δ, RE=rare earth elements) coated conductor (CC) is one of the best candidates for building high-field magnets and it has been improved greatly in recent years. CC overcome the grain boundary problem by using either a rolling assisted biaxially textured substrate (RABiTS) or ion beam assisted deposition (IBAD) of a template for the REBCO. Artificial pinning centers were also introduced to increase critical current density. Despite all these improvements, one significant residual problem is lengthwise critical current (Ic) variations of the CCs. Characterizations of CCs can not only identify the variations, but also provide insight that can help improve the manufacturing process. This study focuses on cross-sectional and vortex pinning variations in CCs. With the reel-to-reel Ic and magnetization measurement system (YateStar), a systematic study has been carried out for CCs made in the last 5-6 years as this technology has rapidly developed. We found that cross-section variations exist for almost all conductors because of width variations. But this contribution to the total Ic variation is small. Vortex pinning variations are found to be the main reason for Ic variations, especially for conductors from different production runs. Even for conductors from the same run, pinning variations are often present. Microscopy studies show that the density and length of BaZrO3 (BZO) nanorods vary between different conductors even though they have nominally the same specifications. Pinning variations in one single tape are mostly attributed to the size variations of BZO nanorods and the configurations of RE2O3 precipitates. Deconstruction of magnet coils and cables were carried out to understand the reasons for in-service degradation. The prototype coil for the 32 T project was safely quenched more than 100 times but it degraded in 3 spontaneous quenches (conducted in an accelerated fatigue testing campaign at ramp rates much larger than service specification). Its pancake coil deconstruction showed three extremely localized burned regions, whose temperature went to over 800oC based on the appearance of a Cu-Ag eutectic above the damaged REBCO layer. Transverse propagation of the damage was almost as effective as longitudinal propagation. Transmission electron microscope images show that thicker BaZrO3 (BZO) nanorods exist near the centers of damaged zones, compared to longer and thinner BZO nanorods from normal, good regions. Because of the lack of detailed Ic(x) characterizations of the length prior to use, the cause the cause of the coil degradation is not clear. It is possible that local degradation of the vortex pinning initiated the final quenches but another possibility is indicated by deconstruction of a no-insulation coil, which reached 45.5 T in a background field of 31 T. In this case no burn marks were observed but some tapes were heavily deformed on one edge, and some joints delaminated after quenches. Transport measurements show that the deformations correlate to Ic degradations, especially for the outer turns of pancakes. Microstructural studies reveal that the deformed (and cracked) edges are always the one that were slit during manufacturing. It appears that small, pre-existing micro-cracks on slit edges propagate after high-field tests. Study of individual strands of conductor on round core (CORC®) cables demonstrated their steady improvements in the last few years. Overall cable current density, Je, has been greatly improved by replacement of 50 m by 30 m thick substrate in CCs and improved winding procedures cause no damage to the tapes. However, some degradation may appear after cables are bent and tested in high-field (20 T). It is found that inner layers are more vulnerable than outer layers. Winding angles and gaps strongly influence where degradations start. To understand the failure mechanisms and establish the limiting winding conditions for CORC® cables/wires, tapes were wound on different formers at different angles: 23o, 30o, 45o and 60o. For a 2 mm former diameter, the highest winding angle gives the least degradation while the other three are comparable. A major defect type introduced during winding is propagation of pre-existing edge (slitting) cracks, but some delamination under winding stress can also be seen. For the former with 2.54 mm in diameter, no propagations of pre-existing cracks or delaminations were observed after winding. Our studies of CCs made and tested in different ways has shown that further improvement of CC and of CORC® cables/wires can be made and also that some inherent features of the manufacture of CCs exert a strong influence on their service performance. / A Dissertation submitted to the Program in Materials Science and Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2017. / November 17, 2017. / Includes bibliographical references. / David Larbalestier, Professor Co-Directing Dissertation; Jan Jaroszynski, Professor Co-Directing Dissertation; Timothy Cross, University Representative; Eric Hellstrom, Committee Member; Christianne Beekman, Committee Member; Theo Siegrist, Committee Member; Dmytro Abraimov, Committee Member.

A bio-inspired, modular terpolymer adhesive has been synthesized containing three different functionalities: a photocrosslinking segment, wet adhesion segment, and a water soluble segment. Wet adhesion is brought on by an amino acid from mussel byssal plaques called 3,4-dihydroxyphenyl–L-alanine, which has been known to generate strong bonding under wet conditions. The photocrosslinking segment consists of an anthracene based monomer used for mechanical fortification of polymer chains. The water soluble segment consists of poly(acrylic acid), which has been known to increase water solubility of polymers and increase adhesion strength of adhesives. The terpolymer was designed to easily applicable using biologically friendly solvents including water and ethanol. Structural design was confirmed by NMR and UV-Vis spectroscopy. Reversible cycloaddition reactions were executed using a handheld UV lamp along with a photoreactor. Molecular weight increases were seen from 4.120 x 10⁴ Da to 7.429 x 10⁴ Da. Lap shear strength testing showed effects of UV exposure through increases in adhesion energy above 450%. Multiple application variables were tested to determine optimal conditions, such as solvent, concentration, and substrate. Currently, optimal conditions show a 1:1 weight ratio of polymer:solvent in water for all surfaces. / A Thesis submitted to the Materials Science and Engineering Program in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2015. / November 5, 2015. / Adhesives, Anthracene, Biomimetic, DOPA, Photo-crosslinking, Terpolymer / Includes bibliographical references. / Hoyong Chung, Professor Directing Thesis; Justin Kennemur, Committee Member; William Oates, Committee Member.

通過與具有表面等離子體激元特性的金屬納米晶複合，半導體納米材料的捕光能力可以得到很大地提高。銀、金納米晶因其獨特的表面等離子體特性，已被廣泛應用于半導體複合物的製備。其中通過沉積或者粘合方式得到的複合物存在一定弊端，比如：金屬納米晶暴露在實驗環境中，導致其團聚、變形、脫落、或者長大，使原有的獨特表面等離子特性改變或消失。核/殼結構納米材料可以有效地避免以上問題，因而表現出優越的光活性。爲了進一步拓寬金屬/半導體核/殼結構在光能捕獲方面的應用，我们需要深入理解製備過程中表面等離子體激元特性及材料結構的變化、設計合成新的納米材料。在這篇畢業論文中，我研究了在製備Ag/Ag2S核/殼結構過程中的表面等離子體特性及材料結構的變化，制備了Au/TiO₂核/殼結構，并對他們的應用及表面等離子體共振激元特性進行了研究。 / 理解硫化過程有助於更好的控制其表面等離子體特性和結構組成。因此，我分別從實驗和數值模擬兩方面研究了銀納米立方塊在硫化過程中表面等離子體特性及其相應Ag/Ag₂S 核/殼的組成及結構的變化。硫化反應分別在溶液及單顆粒環境下進行。同時，我們應用數值模擬計算揭示硫化過程中表面等離子體特性及模式變化。實驗和數值計算均表明硫化反應首先發生在銀納米立方塊的棱角和頂點。隨著反應的進行，銀立方塊被逐步鈍化為球狀銀納米顆粒。與此同時，納米立方結構的尺寸也隨之小幅增加。 / 二氧化鈦是一種重要的被應用於光能捕獲的半導體納米材料。因其低毒性、生物兼容性、化學及熱穩定性、耐光腐蝕性以及資源豐富等特點，TiO₂ 已經被廣泛研究。但是TiO₂僅在紫外光區具有光化學活性，這大大限制了其在光能捕獲方面的應用。儘管Au/TiO₂核/殼結構複合物可以提高TiO₂在可見區的光催化活性，但是對於該核/殼結構的合成鮮為報導，而且已報導的工作也是限制在以金納米球作為核層。與金納米球相比，金納米棒具有更引人關注的表面等離子體特性，例如金納米棒具有更高的電場增強，而且金棒的縱向共振波長可以從可見區調控到近紅外區。因此金納米棒/二氧化鈦核/殼結構可以更有效的提高二氧化鈦的光捕獲能力。在此論文中，我發展了一種合成Au/TiO₂核/殼結構的方法，并研究其在光能捕獲方面的應用。在該方法中，我選擇三價鈦作為鈦源，可控合成了Au/TiO₂ 核/殼結構。通過對核的尺寸及殼層厚度的調節，實現了對核/殼結構的共振波長的調控。另外這種方法也適用于其他單組份或者雙組份的鉑、鈀、金納米晶。爲了驗證在光能捕獲方面的應用潛能，Au/TiO₂核/殼結構納米材料被作為散射層而應用於染料敏化太陽能電池中，結果發現這種電池具有較高光電轉化效率。另外，我們還研究了表面等離子體共振激元增強下的活性氧化物的生成。再者，具有較高介電常數的二氧化鈦殼層可以與金納米晶核耦合產生法諾共振效應。結果表明金納米棒的橫向、縱向共振峰均能和殼層材料發生共振耦合而產生對應的法諾效應。納米棒的縱向共振峰的可調性實現了對應的法諾共振峰的可調性。同時，包覆二氧化鈦殼層后，金納米棒的橫向共振模式被大幅放大。 / 本論文的研究有利於人們了解金屬/半導體納米結構的設計及應用。硫化過程中表面等離子體共振激元特性及結構變化的研究，對具有特定組分及共振特性的複合物的設計合成具有指導意義。對貴金屬/半導體核殼結構製備、共振特性及應用的研究也擴展了其在光能捕獲方面的應用。 / Over the past several years, integration of metal nanocrystals that can support localized surface plasmon has been demonstrated as one of the most promising methods to the improvement of the light-harvesting efficiency of semiconductors. Ag and Au nanocrystals have been extensively hybridized with semiconductors by either deposition or anchoring. However, metal nanocrystals tend to aggregate, reshape, detach, or grow into large nanocrystals, leading to a loss of the unique properties seen in the original nanocrystals. Fortunately, core/shell nanostructures, circumventing the aforementioned problems, have been demonstrated to exhibit superior photoactivities.To further improve the light-harvesting applications of (plasmonic metalcore)/(semiconductor shell) nanostructures, it is vital to understand the plasmonic and structural evolutions during the preparation processes, design novel hybridnanostructures, and improve their light-harvesting performances. In this thesis, I therefore studied the plasmonic and structural evolutions during the formation of (Ag core)/(Ag₂S shell) nanostructures. Moreover, I also prepared (noble metal core)/(TiO₂shell) nanostructures and investigated their plasmonic properties and photon-harvesting applications. / Clear understanding of the sulfidation process can enable fine control of the plasmonic properties as well as the structural composition of Ag/Ag₂S nanomaterials.Therefore, I investigated the plasmonic and structural variations during the sulfidation process of Ag nanocubes both experimentally and numerically. The sulfidation reactions were carried out at both the ensemble and single-particle levels.Electrodynamic simulations were also employed to study the variations of theplasmonic properties and plasmon modes. Both experiment and simulation results revealed that sulfidation initiates at the vertices of Ag nanocubes. Ag nanocubes arethen gradually truncated and each nanocube becomes a nanosphere eventually. The cubic shape is maintained throughout the sulfidation process, with the edge lengthii being increased gradually. / TiO₂ is one of the most important semiconductors that are employed inlight-harvesting applications. It has been extensively studied for a variety of applications by virtue of its low toxicity, biological compatibility, chemical and thermal stability, resistance to photocorrosion, and relative abundance. However, the photocatalytic activity of TiO₂ is limited to the UV region because of its wide bandgap, which limits its applications in light harvesting. Although (Au core)/(TiO₂ shell)nanostructures can improve the photocatalytic activities of TiO₂ in visible light, it hasonly been demonstrated in a few experiments and has been limited with Au nanospheres. Compared with Au nanospheres, Au nanorods offer more attractive plasmonic features, including stronger electric field enhancements and synthetically tunable longitudinal plasmon wavelengths over the visible to near-infrared region. The coating of Au nanorod therefore can largely improve light harvesting capabilityof TiO₂. In this thesis, I developed a facile and versatile method for the preparation of(Au nanocrystal core)/(TiO₂ shell) nanostructures by using a Ti(III) compound as thetitania precursor. By employing Au nanorods with different sizes and varying the shellthickness, the plasmonic bands of the core/shell nanostructures can be tailored. TiO₂can also be grown on other monometallic and bimetallic Pd, Pt, Au nanocrystals. As aproof-of-concept application, (Au nanorod core)/(TiO₂ shell) nanostructures wereutilized in dye-sensitized solar cells to function as a scattering layer. The resultantsolar cells exhibited higher power conversion efficiencies with a thinner thickness compared to the traditional TiO₂ solar cells. In addition, I also examined the property of plasmon-enhanced reactive oxygen species generation. Moreover, the TiO₂ shell with a high refractive index can efficiently couple with the plasmon resonance modesof the Au nanorod core, leading to Fano resonances. Fano resonances for both the transverse and longitudinal plasmon modes were simultaneously observed. The longitudinal Fano resonance is tunable by changing the plasmon energy of thenanorod core. In addition, coating with TiO₂ intensifies the transverse plasmon modeof the Au nanorod core. / I believe that my research study will be very helpful for the design and applications of metal/semiconductor nanostructures. The full understanding of the plasmonic and structural evolutions during the preparation processes will be useful for designing metal/semiconductor hybrid nanomaterials with desired compositions and plasmonic properties. The efforts towards the investigations of the preparation, plasmonic properties, and applications of (noble metal core)/(semiconductor shell) nanostructures are important for widening their light-harvesting applications. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Fang, Caihong = 具有表面等離子體激元特性的金屬/半導體核/殼納米結構 / 房彩虹. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references. / Abstracts also in Chinese. / Fang, Caihong = Ju you biao mian deng li zi ti ji yuan te xing de jin shu/ban dao ti he/qiao na mi jie gou / Fang Caihong.