Dissertations / Theses on the topic 'Nanostructures.;Photolithography.;Plasmons (Physics)'

In principle, the surface plasmon polaritons, at the planar metal/dielectric interface, cannot be excited by incident light. However momentum transfer from incident light to Surface Plasmon Polaritons (SPPs) inside the light line can be achieved by adding a periodic structure at the interface. The lattice wave vector can compensate the difference between incident light and surface wave momentum and satisfy momentum matching requirement. Two methods are commonly used to achieve this goal: first, using prism and second, surface engineering using different array apertures at the metal/dielectric interfaces. In this thesis, the ruled grating pattern at the metal/dielectric interface using conventional photolithography technique was fabricated. The dimension of ruled grating pattern is proportional to expanding/collimating system in the interference set-up. In fact, a large area grating can be utilized for many optoelectronic applications with greater efficiency. In this work, large area grating pattern, 10×10 mm2, on top of the microcavity structure was integrated that permitting cavity mode-SPP coupling. Hence, Rabi-like splitting was observed from the hybrid plasmonic microcavity. The splitting was created from the coupling of cavity mode with the surface plasmon polariton mode; anti-crossing was observed alongside the modal conversional channel on the reflection light measurement. In following, it was experimentally explored the effect of using organic fluorescent molecules inside the hybrid plasmonic microcavity. Accordingly we integrated large area ruled metal grating onto photonic microcavity and assessed the cavity mode-SPP coupling with reflectivity measurement. We got much more grounded modal coupling in presence of florescent molecules within photonic cavity. The anti-crossing was detected with enormous Rabi-like splitting energy at 280 meV in the strong coupling regime. Besides we compared the coupling strength of plasmonic microcavities with various cavity lengths to explore the absorption impact.

Thesis (M. S.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008.
Committee Chair: El-Sayed, Mostafa A.; Committee Member: Lyon, L. Andrew; Committee Member: Sherrill, C. David; Committee Member: Wang, Zhong Lin; Committee Member: Whetten, Robert L.

This thesis is devoted to the experimental investigation of ultrafast dynamics in silicon nanostructures and surface plasmonics by means of femtosecond lasers. First part of the research, ultrafast carriers dynamics in silicon nano-structures, is based on the time-resolved pump-probe reectivity method. A change in the density of excited carriers, as a response to the change of the excitation intensity, was extracted from the time-resolved re ectivity of crystalline nanopillars and nano-inclusions. The measurements were performed mainly in the sub-melting uence regime, at nearly normal incidence to the sample surface plane of the pump and probe beams. Both types of nano-structures have shown strong intensity dependent response comparing to bulk crystalline silicon. This enhanced response is attributed to a suppression of the diffusion processes in nanopillars and nonlinear response due to a constructive multilayer interference between the host matrix material, where silicon inclusions have been embedded, and the sublayers. Electron-phonon and recombination characteristic decay-times are extracted. The second part is devoted to sub-nanosecond decay of photoluminescence from siliconnitride amorphous structures. Particular structures have shown two radiative decay peaks. The second radiative peak is addressed to deep subband tail states, originated by the open bonds of the amorphous structure leading to the long radiative transition. The last part describes femtosecond-resolved plasmon-assisted dissociation of diatomic oxygen molecules in ultrahigh vacuum conditions. Asymmetric gold gratings have been utilised to create enhanced local electric elds originated from the optically excited surface plasmon resonances. Charged products of the dissociation process have been analysed by time-of-light linear drift mass spectrograph, while two-dimensional distribution has been achieved deploying Velocity Map Imaging technique. The dissociation process is found intensity dependent with strong non-linear prole. No correlation has been observed with background plasmon-enhanced electron emission.

In this work, the optical properties of two kinds of one-dimensional (1D) nanomaterials, mesoporous silicon nanowires (mpSiNWs) and plasmonic nanospirals (NSs), were studied. These emerging nanomaterials are of great interest because of their fundamental structure-derived properties and potential practical applications. Four aspects of these materials were analyzed in this work. First, although the fabrication mechanism of mpSiNWs has been studied previously via metal-assisted chemical etching, the porosification-induced disturbance to the etching direction, which plays a vital role in controlling the surface crystallinity of mpSiNWs, has not been characterized. In Chapter 2, I discuss the porosification etching mechanism of n-Si(111), which proceeds along the intrinsic back bond etching direction of [111] at room temperature. The porosification substantially weakens the back bonds under the sinking particles, resulting in the deviation of etching from [111]. The preferred direction of etching changes to that with a small angle α, because the direction-switching barrier increases with α and intrinsic back-bond etching is thermodynamically preferential. Second, mpSiNWs typically generate red photoluminescence (PL), but the PL mechanism is still under debate. A laser was used to oxidize the surfaces of mpSiNWs and tune the PL from red to greenish-blue (GB), as described in Chapter 3. The laser oxidation was tuned as a function of laser power, and a complex model of the laser-induced surface modification was proposed to account for the laser-power and post-annealing effect. The laser-induced modification of the PL of mpSiNWs may be useful for data encryption. Third, the fabrication of plasmonic NSs and the study of their optical activities are in their infancy. In Chapter 4, I describe the use of glancing-angle deposition (GLAD) to fabricate silver NSs (AgNSs) with controllable helicity and demonstrate that AgNSs have intrinsic optical responses that originate from their structural helicity. The optical activity of an AgNSs dispersion was characterized by circular dichroism (CD), and systematic engineering of the helicity revealed that their UV and visible optical activities have two different origins. Fourth, physical limits prohibit the sensitive differentiation of enantiomers. In Chapter 5, I describe the grafting of chiral molecules onto AgNSs, which dramatically enhanced the differentiation of L- and D-glutathione (GSH). AgNSs have very strong optical activities that are weakened by GSH adsorption. The severity of the chiroptical weakening effect varies with the absolute configuration of GSH, resulting in enantiomeric differentiation with an anisotropic g-factor of approximately 0.5. This chiral nanoplasmon-induced anisotropy g-factor is superior by 2 to 4 orders of magnitude to those obtained with other methods and about one-fourth of the theoretical value. This proposed method can be adapted to differentiate chiral drugs, which is highly desirable in the pharmaceutical industry for the production of single-enantiomer drugs.

Les nanocristaux semi-conducteurs sont des objets de dimensions nanométriques aux niveaux d'énergie quantifiés. Grâce à leurs propriétés de fluorescence, ils trouvent des applications dans des domaines aussi variés que la biologie, l'opto-électronique ou l'optique quantique. Pour toutes ces applications, un contrôle de leurs propriétés d'émission est primordial. Dans ce cadre, après une étude fine de leurs propriétés d'émission à température cryogénique, nous nous sommes intéressés à leur couplage avec les plasmons de couches d'or désordonnées. Nous montrons alors la possibilité de supprimer efficacement les fluctuations d'intensité d'émission, d'accélérer drastiquement l'émission de photons et de créer des cascades bi-excitoniques.

Grâce à ses propriétés optiques originales, une NanoParticule d’Or (NPO) excitée peut se comporter comme une nano-source de lumière, de chaleur et d’électrons chauds. Ces propriétés plasmoniques remarquables sont exploitées dans de nombreuses transformations chimiques. Dans ce contexte, la photocatalyse plasmonique basée sur le transfert d’électrons entre une NPO et un semi-conducteur a été proposée. Cependant, peu d’études sont centrées sur l’influence du plasmon et la contribution respective de ses effets locaux (thermiques et électroniques) sur ce transfert utilisé en photocatalyse. Ici, nous abordons ces problématiques à travers 3 réactions catalytiques. Premièrement, nous montrons la faisabilité de l'oxydation efficace et sélective de glycérol sans aucune source externe de chaleur grâce à l’effet thermoplasmonique local de la NPO. Nous étudions ensuite la dégradation de bisphénol-A sur différents supports catalytiques. Nos résultats montrent que la NPO joue un rôle primordial à travers le transfert d’électrons mais aussi en tant que nano-source de chaleur permettant d’accélérer la cinétique et d’éliminer ainsi totalement et rapidement ce perturbateur endocrinien. Enfin, nous avons développé un montage optique pour étudier la dégradation de polluants à l'échelle nanométrique. Pour cela, nous avons réalisé un système hybride à base de NPOs couplées à un nanofilm de TiO2 par structuration laser. Nos travaux montrent que l’activité catalytique est corrélée aux dimensions structurales des NPOs. Ces résultats ouvrent la voie vers l'exploitation de nombreux processus industriels sous lumière solaire
The excitation of Localized Surface Plasmon Resonance (LSPR) of Gold NanoParticles (GNPs) can give many physical effects such as near-field enhancement, heat generation and hot electron injection, which have been investigated in many chemical transformations. In that context, the plasmonic photocatalysis based on electron transfer from GNP to a semi-conductor has been proposed. However, few studies are focused on the influence of LSPR features and the respective contribution of its local effects (thermal and electronic) on the photocatalytic activity. These issues are addressed herein through 3 catalytic reactions. First, the efficient and selective oxidation of glycerol in the presence of supported GNPs is demonstrated under laser irradiation and without any external source of heat, thanks to the local heat generation and hot electron transfer. The respective contributions of these effects is further investigated in plasmonic photocatalysis by following the degradation of Bisphenol-A. Our results show that GNP plays a major role through hot electron transfer but also as a nano-source of heat that accelerates the reaction and leads to a fast and total elimination of this endocrine disruptor. Finally, an optical set-up is developed for studying the plasmonic photocatalysis at the nanoscale. For this, a hybrid system of GNPs coupled to a TiO2 nanofilm is realized by laser nanostructuring. Our investigations show that photocatalytic activity is correlated to the LSPR (size and shape of GNPs, hot spots). These results open the way for exploiting valuable and industrial reactions under solar light

Nous présentons les principales propriétés quantiques de fluorescence de nanocristaux de CdSe/CdS individuels à température ambiante. Nous montrons la quasi-suppression de scintillement et l'allongement des durées de vie radiative de ces nanocristaux à la coquille épaisse et de leur rendement quantique. Nous prouvons expérimentalement, par microscopie confocale en champ lointain, que l'interaction d'un nanocristal avec des nanostructures métalliques, réduit sa durée de vie radiative et modifie les efficacités des processus radiatifs et non-radiatifs. Nous montrons que, le couplage dépend bien de la position du nanocristal et que pour certains nanocristaux une large fraction des plasmons est diffractée par la structure spatiale de la couche. Nous obtenons des facteurs de Purcell très importants. Enfin, nous expliquons la relation entre les états d'émission et la compétition entre processus Auger et radiatifs.

Les biocapteurs optiques ont connu une évolution sans précédent au cours des dernières années, principalement en raison de la forte interaction entre la biotechnologie, l’optique et la chimie des matériaux. Dans cette thèse, deux différentes plates-formes de biocapteurs optiques ont été conçues pour la détection sensible et spécifique des biomolécules. Plus précisément, le premier système de détection optique est construit sur la base de la bioluminescence de cellules bactériennes d'Escherichia coli génétiquement modifiées. L’émission de lumière induite par cette interaction peut donc être utilisée pour la détection des substances toxiques. Le second système utilise des nanoparticules de métaux précieux (or et argent) aux propriétés plasmoniques accordables qui permettent de sonder les interactions des biomolécules spécifiques à l'interface nano-bio par la résonance plasmonique de surface (LSPR). Ces nanoparticules ont été obtenues par traitement thermique à haute température d’un film métallique déposé sur du verre à l’aide d’une grille de TEM ou déposé sur une couche de bactéries fixée sur le verre. Après une optimisation appropriée des nanostructures métalliques en termes de morphologie et de fonctionnalisation, une sensibilité élevée et une grande spécificité peuvent être simultanément obtenues avec ces immunocapteurs plasmonique. Ces deux plateformes ont été utilisées pour détecter des pesticides comme le carbofuran et l’atrazine
Optical biosensors have witnessed unprecedented developments over recent years, mainly due to the lively interplay between biotechnology, optical physics and materials chemistry. In this thesis, two different optical biosensing platforms have been designed for sensitive and specific detection of (bio)molecules. Specifically, the first optical detection system is constructed on the basis of bioluminescence derived from engineered Escherichia coli bacterial cells. Upon stressed by the toxic compounds, the bacterial cells produce light via a range of complex biochemical reactions in vivo and the resulted bioluminescent evolution thus can be used for toxicant detection. The bacterial bioluminescent assays are able to provide competitive sensitivity, while they are limited in the specificity. Therefore, the second optical detection platform is built on the localized surface plasmon resonance (LSPR) immunosensors. In this optical biosensor, the noble metal (gold and silver) nanoparticles with tunable plasmonic properties are used as transducer for probing the specific biomolecules interactions occurred in the nano-bio interface. These nanoparticles were obtained after a high temperature thermal treatment of an initially thin-metallic film deposited on a glass substrate through a TEM grid or on a bacteria layer fixed on the glass. After appropriate optimization on metal nanostructures morphology and surface biomodification, the applicable sensitivity and specificity can be both guaranteed in this LSPR immunosensor

La surface d'un matériau exposé à une irradiation laser à une fluence proche de son seuil d'ablation laisse apparaître des structures périodiques LIPSS (Laser Induced Periodic Surface Structure) d'orientation dépendant de la polarisation de faisceau incident et dont la période est de l'ordre de la longueur d'onde. Les causes de ce phénomène qui suscite l'attention des chercheurs depuis plus d'une trentaine d'années sont maintenant bien connues. Cependant, son étude dans le cadre de l'utilisation récente de lasers à impulsions ultra-brèves fait surgir de nouvelles interrogations et relance l'intérêt pour le sujet. Ce travail est consacré à l'étude dynamique de la formation des nanostructures sur une surface métallique suite à une interaction laser femtoseconde. Nous nous intéressons aux mécanismes responsables de la formation de ces structures et nous proposons des explications permettant de comprendre leur origine. Dans le premier chapitre on présente une étude de l'état de l'art sur la formation des LIPSS, on y aborde les paramètres influant sur la formation de ces structures ainsi que les différents modèles explicatifs élaborés par les chercheurs. Ce chapitre traite également de l'interaction laser matière et de ses différents processus. Le deuxième chapitre met l'accent sur les dispositifs expérimentaux réalisés dans ce cadre. Le troisième chapitre présente, quant à lui une étude expérimentale permettant de rendre compte du rôle de l'excitation du plasmon de surface dans la formation de LIPSS. Dans le quatrième chapitre on analyse les résultats relatifs à l'influence du couplage électron phonon sur la formation des LIPSS. Enfin, le cinquième et dernier chapitre met en évidence le rôle de la relaxation électron-phonon sur la formation des LIPSS à l'aide d'une expérience pompe-sonde.

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008.
Committee Chair: El-Sayed, Mostafa A.; Committee Member: Perry, Joseph W.; Committee Member: Srinivasarao, Mohan; Committee Member: Whetten, Robert L.; Committee Member: Zhang, Z. John.

"There is plenty of room at the bottom." This bold and prophetic statement from Nobel laureate Richard Feynman back in 1950s at Cal Tech launched the Nano Age and predicted, quite accurately, the explosion in nanoscience and nanotechnology. Now this is a fast developing area in both science and technology. Many think this would bring the greatest technological revolution in the history of mankind. To understand electronic and optical properties of nanostructures, the following problems have been studied. In particular, intensity of mid-infrared light transmitted through a metallic diffraction grating has been theoretically studied. It has been shown that for s-polarized light the enhancement of the transmitted light is much stronger than for p-polarized light. By tuning the parameters of the diffraction grating enhancement can be increased by a few orders of magnitude. The spatial distribution of the transmitted light is highly nonuniform with very sharp peaks, which have the spatial widths about 10 nm. Furthermore, under the ultra fast response in nanostructures, the following two related goals have been proved: (a) the two-photon coherent control allows one to dynamically control electron emission from randomly rough surfaces, which is localized within a few nanometers. (b) the photoelectron emission from metal nanostructures in the strong-field (quasistationary) regime allows coherent control with extremely high contrast, suitable for nanoelectronics applications. To investigate the electron transport properties of two dimensional carbon called graphene, a localization of an electron in a graphene quantum dot with a sharp boundary has been considered. It has been found that if the parameters of the confinement potential satisfy a special condition then the electron can be strongly localized in such quantum dot. Also the energy spectra of an electron in a graphene quantum ring has been analyzed. Furthermore, it has been shown that in a double dot system some energy states becomes strongly localized with an infinite trapping time. Such states are achieved only at one value of the inter-dot separation. Also a periodic array of quantum dots in graphene have been considered. In this case the states with infinitely large trapping time are realized at all values of inter-dot separation smaller than some critical value.

L'objectif de cette thèse est l'étude de nanostructures d'or ayant un rapport de forme important (nanofils, pointes...), assimilables à des nanoantennes optiques. Ainsi, j'ai tout d'abord étudié la diffusion Raman exaltée de surface (SERS) de réseaux de nanofils d'or de forme et de taille contrôlées produits par lithographie électronique. Je me suis notamment intéressé à l'influence des plasmons de surface localisés sur l'efficacité SERS de ces nanofils. Nous avons ainsi observé les plasmons de surface d'ordre supérieur jusqu'à 7. Nous avons alors relié l'exaltation SERS à la position de la résonance plasmon et déterminé l'efficacité des ordres supérieurs. Nous avons également mis en évidence que le maximum d'exaltation est obtenu pour une résonance plasmon proche de la longueur d'onde de diffusion Raman et ceci pour deux excitations laser différentes.
Ensuite, j'ai monté une expérience de Raman en champ proche (ou TERS) et développé une technique reproductible de fabrication de pointes en or. Puis, j'ai effectué une étude quantitative des propriétés de dépolarisation des pointes métalliques utilisées en a-SNOM et en TERS. Nos résultats montrent des facteurs de dépolarisation entre 5 et 30% qui varient en fonction de la polarisation de la lumière incidente et de la forme de la pointe. Les conséquences importantes de ce phénomène de dépolarisation ont été mises en évidence dans des expériences TERS sur du Silicium cristallin; On montre que la dépolarisation doit être prise en compte pour une estimation correcte de l'exaltation induite par la pointe.

Dans ce travail, nous avons étudié l'interaction entre une lumière contrôlée en polarisation et deux structures sub-longueurs d'onde gravées dans un film métallique opaque, en utilisant la méthode de la " matrice de Mueller ". Tout d'abord, nous avons montré qu'un réseau concentrique de fentes sub-longueurs d'onde percées à travers le film permet de filtrer et de convertir une polarisation incidente, ce qui génère une polarisation radiale. Nous avons aussi montré sa capacité à générer des faisceaux de Bessel non-diffractifs J0 ou J2 à travers de telles structures, et à contrôler leur hélicité en changeant la polarisation circulaire en préparation ou en analyse. Ensuite, nous avons montré la création d'une cible plasmonique ayant les propriétés d'une lame quart d'onde, en travaillant sur l'ellipticité des anneaux - pour générer une phase plasmonique - etdu trou central - pour compenser les forts effets de dichroïsme induits par l'absorption différentielle des plasmons de surface.

Le présent document constitue le mémoire rédigé durant ma thèse de doctorat, qui s'est déroulée de novembre 2008 à novembre 2011 à l'Institut Langevin (ESPCI ParisTech). Une partie de ce travail de thèse a consisté en l'étude expérimentale des fluctuations spatiales de la densité de modes optiques (LDOS) à la surface de films d'or semi-continus, connus pour présenter des modes de surface localisés au voisinage du seuil de percolation. Pour cela, nous avons dispersé des nanosources fluorescentes à la surface de films de fraction surfacique d'or croissante et mesuré la statistique du taux d'amortissement des émetteurs. Nous avons montré que les fluctuations spatiales de LDOS sont maximales lorsque les modes localisés apparaissent. Nous avons ensuite développé un instrument permettant de réaliser l'imagerie de LDOS en accrochant une nanosource fluorescente à l'apex d'une pointe d'AFM, et réalisé une preuve de principe sur des échantillons de test. Une autre partie a concerné l'étude théorique de la réponse optique d'une nanoparticule métallique. Nous avons montré comment le taux d'amortissement d'un dipôle en champ proche d'une nanosphère métallique est modifié lorsque les interactions microscopiques sont prises en compte. Nous avons également étudié l'influence de l'environnement sur la section efficace d'absorption d'une nanoparticule, et montré que cette grandeur n'est pas intrinsèque, mais dépend de l'environnement. Nous avons confirmé ce résultat sur un exemple simple permettant de donner des ordres de grandeur.

Certains matériaux ont des modes électromagnétiques confinés à leur surface, qui se
propagent le long de celle-ci. Ces modes, qui sont appelés ondes de surface, peuvent être couplés à des ondes propagatives à l'aide d'un réseau.
Nous avons utilisé un code de calcul électromagnétique exact, basé sur l'analyse rigoureuse des ondes couplées (RCWA), pour optimiser des structures périodiques dont les dimensions sont de l'ordre ou inférieures au micron. Nous avons ainsi conçu des micro ou nanostructures pour deux types d'applications : l'émission thermique cohérente, et la transmission résonante.
En émission, nous avons optimisé des sources thermiques émettant un rayonnement
quasi-monochromatique dans une direction privilégiée de l'espace ou bien dans toutes les directions. Nous avons de plus conçu, dimensionné et mis en place un montage de mesure de l'émissivité de telles sources. Nous avons pu retrouver de manière quantitative les résultats que nous avons obtenus numériquement, puis déterminer expérimentalement la longueur de cohérence spatiale de la source.
Le second axe de cette thèse a été consacré à la transmission résonante. Nous avons
mis en évidence les mécanismes de transmission de structures métalliques en montrant l'existence de modes propres de ces structures qui sont des modes couplant modes de surface et modes de cavité. En remontant aux caractéristiques de ces modes, nous pouvons en particulier retrouver toutes les caractéristiques des pics de transmission, hauteur, largeur et position. Nous avons par ailleurs montré que des effets analogues apparaissent pour des réseaux de cristaux polaires. Finalement, des études de transmission résonante par des cristaux 2D ont montré que des modes d'ordre élevé peuvent être fortement transmis. Ces modes sont faiblement couplés à des ondes planes mais peuvent se coupler fortement à des particules ou molécules.

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Dans cette thèse nous avons ajouté le contrôle du paramètre spectral pour donner plus de degré de liberté à l'instrument basé sur l'Imagerie par Résonance des Plasmons de Surface (SPRI), développant un système instrumental à interrogation angulo-spectrale. Pour valider notre travail, nous avons pris comme modèle d'étude un milieu diélectrique absorbant à unelongueur d'onde visible. La fonction diélectrique complexe est traitée par le modèle de Lorentz et la relation entre la partie réelle et imaginaire de l'indice optique est assurée par la relation de Kramers-Kronig. Nous avons commencé par injecter dans la cellule de mesure un colorant absorbant à 630 nm et mesuré la réflectivité angulo-spectrale avec ce milieu. Ensuite, un programme d'ajustement, que nous avons développé, a été utilisé pour le calcul inverse et la détermination des paramètres optiques à partir des données de l'expérience. Cet ajustement permet d'extraire la partie réelle et la partie imaginaire de l'indice de réfraction démontrant la possibilité d'applications de type spectroscopique. Nous avons également intégré successivement à la surface des molécules d'ADN marquées par différents chromophores pour voir l'effet de la position d'absorption sur la variation de réflectivité angulo-spectrale. En plus des milieux absorbants, nous avons fabriqué des réseaux diélectriques et métalliques et les avons intégrés à la surface du prisme. Les structures utilisées avaient une période de 250 nm et une épaisseur de 300 nm en PMMA. Cette condition nous a permis de voir un plasmon bandgap centré à 735 nm. Cette étude expérimentale est validée par une étude théorique en utilisant la méthode RCWA pour simuler la réponse des réseaux périodiques.

Le travail présenté dans ce manuscrit a permis de mettre en lumière les différentes possibilités menant à l'optimisation de l'efficacité de capteurs basés sur la résonance de plasmons de surface localisé (RPSL) et fabriqués par des techniques contrôlant précisément la géométrie des nanostructures métalliques. L'accent a été mis plus particulièrement sur les capteurs par RPSL et sur les capteurs par diffusion Raman exaltée de surface (DRES). Le premier chapitre a rappelé les paramètres clés menant à l'optimisation recherchée, i.e., la nature du métal, la taille de la nanoantenne, sa forme, son milieu environnant, la polarisation du champ électrique incident, la séparation entre les nanoparticules et la présence d'ordres supérieurs. Le second chapitre s'est davantage centré sur les capteurs DRES en exposant le principe et les possibilités d'optimisation de leur signal dans le cas de rangées de nanostructures d'or. Le chapitre 3 s'est consacré à l'observation de l'allure du champ électromagnétique local (amplitude et longueur de décroissance) par l'étude du couplage champ proche entre les nanoparticules d'or.

In this thesis devices for controlling the flow of surface plasmon polaritons are described. Dielectric and metallic nanostructures were designed for this purpose, and characterized by leakage radiation microscopy in real and in reciprocal spaces. Manipulation of surface plasmons by dielectric lenses and gradient index elements is presented, and negative refraction, steering and self-collimation of surface plasmons in one- and two-dimensional plasmonic crystals is demonstrated. The achieved degree of control was applied for routing of nanoparticles by optical forces, as well as for two methods of enhancing the figures of merit of plasmonic refractive index sensors, based on the one hand on Fano resonances natural to leakage radiation microscopy, and on the other hand on anisotropie plasmonic bandstructures.

各種納米結構的光學反應，已成為一被相當關注的課題，在物理理論和應用技術的層面上被廣泛研究。在本文中，我們利用格林函數方法(GFF)，研究了新月形圓柱体和兩接近中的圓柱体的靜電共振。格林函數方法裏涉及一表面積分方程式，我們求該方程的解便可以得出各不同形狀的納米結構的電勢。格林函數方法是一容易使用、高效率的方法，並且在研究納米結構的光學行為的問題上得出準確結果。
在論文的第一部分，我們計算了新月形圓柱体和兩接近中的圓柱体的杆光譜，從而研究該兩個結構的靜電共振。然而，當這兩個結構中有接觸點時，系統中便有一奇點，因此我們不能直接使用格林函數方法研究這情況。為了解決這問題，我們首先使用了變換光學的方法，求得該結構的雙極因子，再從中得到其有效介電常數的譜密度。為了比較非接觸情況中離散的杆光譜和接觸情況中的連續杆光譜，我們進一步定義了一累積分佈函數，它是其譜密度的累積分佈函數。我們從而發現當系統由非接觸的情況漸近接觸時，其離散的杆光譜便趨向其相應的連續杆光譜。
在論文的第二部分，我們直接研究了新月形圓柱体和兩接近中的圓柱体的勢分佈和電埸分佈。我們發現在新月形圓柱体和兩接近中的圓柱体的系統中，能量會分別將集中於其金屬間隔和空氣間隔附近的區域。當我們適當地選擇系統的參數時，其共振及能量更能進一步增強。我們亦確認了使用格林函數方法和使用保角變換方法兩者得出的結果的是吻合的。我們的研究結果可以幫助設計電漿子捕光裝置。
The optical responses of various nanostructures have attracted a considerable attention and they have been extensively studied from the theoretical and technological points of view. In this thesis, we have studied the electrostatic resonance of crescent-shaped cylinder and two approaching cylinders by the Green function formalism (GFF). In the GFF, a surface integral equation is formulated for the scalar potential for an arbitrary number of nanostructures of various shapes. GFF is easy to apply and gives accurate results for the optical behaviors of these nanostructures.
In the first part of the thesis, we have studied the electrostatic resonance of crescent-shaped cylinder and two approaching cylinders by calculating the pole spectrum. However, in the touching case, there is a singular point and thus the GFF cannot be applied directly. To circumvent this problem, the spectral density is found from the polarizability of the nanostructure, which can be obtained analytically by the transformation optics approach. To compare the discrete pole spectrum of the non-touching cases with the continuous spectrum of the touching case, we have used the cumulative distribution function of the spectral density. We are then able to show that the discrete pole spectrum approaches to the continuous pole spectrum as the system approaches from non-touching cases to the touching case.
In the second part of the thesis, the electrostatic resonance is investigated by directly finding the local field distributions of crescent and two approaching cylinders under a uniform applied electric field. It is shown that there is an energy concentration within the metal narrow gap and the air narrow gap in the cases of crescent and two approaching cylinders respectively. It is also found that when parameters are carefully chosen, the nanoconcentration of energy will be greatly enhanced. The numerical GFF results are confirmed with the analytic results by conformal transformation. The results are useful in designing plasmonic light-harvesting devices.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Yung, Sai Kit = 電漿子納米結構中的能量集中 : 格林函數方法 / 翁世杰.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2012.
Includes bibliographical references (leaves 71-74).
Abstracts also in Chinese.
Yung, Sai Kit = Dian jiang zi na mi jie gou zhong de neng liang ji zhong : Gelin han shu fang fa / Weng Shijie.
Abstract --- p.i
摘要 --- p.iii
Acknowledgements --- p.iv
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Optical responses in plasmonic systems --- p.1
Chapter 1.2 --- Objective of the thesis --- p.5
Chapter 2 --- Review on Green function formalism --- p.7
Chapter 2.1 --- Integral equation formalism --- p.7
Chapter 2.2 --- Periodic corrugated interfaces --- p.11
Chapter 2.3 --- Solution by mode expansion --- p.16
Chapter 2.4 --- Numerical solution --- p.18
Chapter 3 --- Pole spectrums of crescent-shaped cylinder and approaching cylinders --- p.21
Chapter 3.1 --- Review of Green function formalism on the spectral representation of the effective dielectric constant --- p.22
Chapter 3.2 --- Numerical results --- p.29
Chapter 3.2.1 --- Spectral representation of the effective dielectric constant of crescent-shaped cylinders --- p.29
Chapter 3.2.2 --- Spectral representation of the effective dielectric constant of approaching cylinders --- p.37
Chapter 4 --- Energy concentration of crescent and approaching cylinders --- p.44
Chapter 4.1 --- Energy concentration of crescent-shaped cylinder --- p.45
Chapter 4.2 --- Energy concentration of approaching cylinders --- p.53
Chapter 5 --- Conclusion --- p.58
Chapter 5.1 --- Suggestion of future works --- p.60
Chapter A --- Conformal transformation --- p.61
Chapter A.1 --- Conformal transformation on crescent-shaped cylinder: nontouching case --- p.61
Chapter A.2 --- Conformal transformation on approaching crescent-shaped cylinders --- p.66
Bibliography --- p.71

基於表面等離子體的納米器件已經在近幾十年引起了十分廣泛的興趣因為其對於半波長光子器件，光學傳感，光譜學以及光學捕獲有著廣大的應用前景。表面等離子體是一種被限定於金屬和介質介面上的一種光子-電子混合模式，而且它具有許多吸引人的特質，比如對金屬表面周圍環境極其敏感，納米尺度範圍的光學電磁場局域和場增強，以及對鄰近物體極強的場強梯度捕獲力。雖然這些特性都已經分別被廣泛的研究過，但從光學捕獲的角度去實現光學傳感的方案並還沒有引起大量的關注。很明顯，在納米尺度範圍內操縱目標的可能性將使得新的納米器件具有高的光學探測性能和多功能性。為了涉及這個論題，本項目包括新穎的等離子體納米器件的研究，這些納米器件將能夠提供獨特的功能，在光學傳感，表面增強拉曼散射，以及光學捕獲方面。
在第一部分設計中，構建了一種基於雙層金屬納米條陣列的耦合系統。這樣的系統具有簡單的結構，易於加工和集成於微流系統的優點。由於這個系統內的光場耦合，場強可以進一步的被加強，這樣的特點有助於提高系統的敏感特性，尤其是通過強的光場來捕獲一些金屬的納米顆粒後。這個系統的光學共振條件可以從理論上進行模式分析得到。然後二維時域有限差分法證實了理論的分析而且進一步證明了利用該系統於光學傳感和捕獲的可能性。結果表明此系統的光學敏感度約為200nm/RIU，通過光學捕獲的金屬納米顆粒引起的近場調製和場增強可以使得表面增強拉曼散射的增強因數達到10⁹ 到10¹° 的高度。
在第二部分的設計裡，金納米環結構被證實了可以成為一個強大的工具作為表面等離子體納米光鑷來抓獲金屬納米顆粒。首先，金屬納米環具有很多優點比如對入射光的偏振不敏感，很寬的可調的共振範圍，有環的內腔周圍和內部有著均勻的光學場增強，以及很容易製備。這裡的設計著重于納米環在入射波長為785nm 的新穎的光學捕獲特性以及表面增強拉曼散射的性能。三維的時域有限差分法被用來計算結構的光學回應，以及麥克斯韋應力張量法被用來計算光學受力分佈情況。計算結果表明對於一個有20nm 大小的金納米顆粒球，納米環結構有最大的光學捕獲勢阱約32 KgT 。由於納米環結構周圍存在多個捕獲勢阱，使得其對目標捕獲顆粒具有約10⁶nm³ 的非常之大的有效體積。而且，被捕獲的顆粒會進一步的導致一些納米間隙的形成，這些納米間隙又會使得近場增強達到約160 倍的高度，這使得在實際應用中10⁸ 的表面增強拉曼散射的增強因數成為可能。
在第三部分的設計裡，全光納米操縱的概念被提出並證實，因為這樣的概念拓展了等離子體光鑷的一個極其重要的功能，那就是被捕獲的分子可以在捕獲和區域內被任意的操縱和轉移，而且這個區域是納米尺度的。設計的系統由梯度形金屬納米盤組成，這些納米盤具有不同的直徑，這使得它們支援不同波長的表面等離子體共振。通過改變入射光的波長和旋轉入射光的偏振態，就可以將捕獲的目標從一個納米盤轉移到另一個納米盤。三維的時域有限差分法和麥克斯韋應力張量法被用來證實了所提出的觀點。計算結果表明被捕獲的目標感受到的捕獲勢阱深度高達5000kgT/W/μm²，最大的光學轉矩約為336pN·nm/W/μm²，而且總的有效捕獲體積可達到10⁶nm³ 。在這部分的結尾，討論了所設計的系統在光學傳感方面潛在的應用前景。
在最後的部分裡，展示了一個實驗的證明來說明等離子體納米光鑷對目標捕獲的觀測問題，因為這樣的觀測對往後近期的相關實驗來說是首先要關心的問題。雖然兩種途徑已經在別處被證實了，分別是通過觀測系統的透射光的強度變化和系統共振波長的改變，來監測表面等離子體納米光鑷近場捕獲行為的發生，但是在這個部分裡，等離子體納米光鑷和表面增強拉曼傳感技術被結合在了一起並且被證實了這是另一種有效的方法用於觀測捕獲行為的發生。在本實驗中兩束鐳射光束被為別用來激發等離子體納米光鑷和表面增強拉曼信號，一束是633nm 的鐳射，另一束是785nm 的鐳射。表面等離子體納米光鑷簡單地由熱蒸鍍並熱退光的金顆粒納米島墊底構成，這個墊底的共振峰被調製到緊靠633nm 的位置。目標顆粒是由光化學生長合成的銀納米十面體，這些十面體被綁定了4-巰基苯甲酸分子的單分子層，且具有遠離633nm 和785nm 的共振峰。由於當等離子體納米光鑷被激勵的時候目標顆粒會被捕獲到近場的熱點內，這時近場的光場就會被極大的增強，所以表面增強拉曼的信號就會出現。這個過程也被用數值模擬的方法（三維時域有限差分法和麥克斯韋應力張量法）闡明了。更進一步的，當等離子體納米光鑷不被激勵的時候，被捕獲的目標顆粒可以被釋放掉，那樣表面增強拉曼的信號就會消失掉。所以，本設計不僅提供了一種強有力的探測等離子體光鑷捕獲行為的方法，而且能夠成為一種在生物探測方面可重複利用的“捕獲并傳感“的平臺。
Surface plasmons (SPs) based nanodevices have attracted much research interest in recent decades due to their powerful application potentials for subwavelength optical circuits, optical sensing, spectroscopy, and optical trapping. SPs are the hybrid photon-electron modes bound at the interface of conductors and transparent materials, and they have lots of attractive properties such as sensitive to the changes of environment around the interface, strong optical field localization and enhancement in nanoscale domain, and strong field intensity gradient forces to trap the adjacent objects. Even though these properties have been widely investigated, their application in optical sensing based on the plasmonic optical trapping strategy remains largely unexplored. Clearly, the possibility of manipulating objects within the nanometer regime will enable new nanodevices that offer high optical detection performance and multiple-functionality. With the aim to address this issue, this project involves the study of novel plasmonic nanodevices that provide unique functionality in optical sensing, surface-enhanced Raman scattering (SERS), and optical trapping.
The first design is based on a coupling system involving double-layered metal nano-strips arrays. This system has the advantages of simple geometry and direct integration with microfluidic chips. The intense optical localization due to field coupling within the system can enhance detection sensitivity of target molecules, especially by virtue of the optical trapping of plasmonic nanoparticles. The optical resonant condition is obtained theoretically through analyzing the SPs modes. Numerical modeling based on two-dimensional (2D) finite-difference time-domain (FDTD) is consistent with the theoretical analysis and demonstrates the feasibility of using this system for optical sensing and trapping. Simulation results show that the refractive index sensitivity can reach ~200 nm/RIU, and a maximum SERS enhancement factor (EF) of 10⁹-10¹° is possible because of the near-field modulation and enhancement from optically trapped metal nanoparticles.
In the second design, a gold nano-ring structure is demonstrated to be an effective approach for plasmonic nano-optical tweezers (PNOTs) for trapping metallic nanoparticles. The plasmonic nano-ring structure has many interesting merits such as polarization insensitivity, wide tunable resonance range, uniform field enhancement around and inside the ring cavity, and ease of fabrication. This design has a unique feature of having large active volume for trapping. In our demonstration example, we have optimized a device for SERS operation at the wavelength of 785 nm. Three-dimensional (3D) FDTD techniques have been employed to calculate the optical response, and the optical force distribution have been derived using the Maxwell stress tensor (MST) method. Simulation results indicate that the nano-ring produces a maximum trapping potential well of ~32 kgT on a 20 nm gold nanoparticle. The existence of multiple potential well results in a very large active trapping volume of ~10⁶ nm³ for the target particles. Furthermore, the trapped gold nanoparticles further lead to the formation of nano-gaps that offer a near-field enhancement of ~160 times, resulting in an achievable EF of 10⁸ for SERS.
In the third design, we propose a concept of all-optical nano-manipulation. We show that target molecules, after being trapped, can be transferred between the trapping sites within a linear array of PNOTs. The system consists of an array of graded plasmonic nano-disks (NDs) with individual elements coded with different resonant wavelengths according to their dimensions. Thus, by switching the wavelength and rotating the polarization of the excitation source, the target nanoparticles trapped by the device can be manipulated from one ND to another. 3D FDTD simulation and MST calculation are utilized to demonstrate the operation of this idea. Our results reveal that the target experiences a trapping potential strength as high as 5000 kgT/W/μm², maximum optical torque of ~336 pN·nm/W/μm², and the total active volume may reach ~10⁶ nm³. The potential applications in terms of optical sensing are also discussed.
In the final design, for which experimental demonstration has been conducted, we show that PNOTs are achievable with random plasmonic nano-islands. Operation of the random PNOTs can be monitored by measuring the SERS enhancement factor in real time. Two laser beams having wavelengths of 633 nm and 785 nm are utilized to stimulate the PNOTs and excite the Raman signals simultaneously. The PNOTs are formed by annealing of a thermal evaporated gold film. This so-called nano-island substrate (Au-NIS) has a resonant peak close to 633 nm. The target is photochemical synthesized silver nanodecadedrons (AgNDs) functionalized with 4-Mercaptobenzoic acid (4-MBA) and the resonant peak of these AgNDs is far away from 633 nm and 785 nm. As the target is trapped to the hot-spots when the PNOTs are active, the near-field intensity is enhanced significantly, which results in the emergence of SERS signals, i.e. confirming the expected outcome of SERS upon nanotrapping by the PNOTs. This process is also elucidated numerically through 3D FDTD simulation and MST calculation. Furthermore, the target can be released as the PNOTs become inactive, i.e. disappearance of the SERS signal. Therefore, this design offers not only a robust avenue for monitoring trapping events in PNOTs, but also a reproducible “trap-and-sense“ platform for bio-detection.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Kang, Zhiwen.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2013.
Includes bibliographical references (leaves 146-170).
Abstracts also in Chinese.
Abstract --- p.I
Acknowledgements --- p.VIII
List of Illustrations --- p.XIII
Chapter Chapter 1. --- Introduction --- p.1
Chapter 1.1 --- Surface Plasmon Polaritons and Localized Surface Plasmons --- p.1
Chapter 1.2 --- Relevant Applications Based on Surface Plasmons --- p.3
Chapter 1.3 --- Plasmonic Nano-Optical Tweezers and Relevant Applications --- p.7
Chapter 1.4 --- Literatures Review and Objectives of this Thesis --- p.12
Chapter 1.5 --- Structure of this Thesis --- p.17
Chapter Chapter 2. --- Research Methodologies --- p.20
Chapter 2.1 --- Theoretical Background of Surface Plasmons --- p.20
Chapter 2.2 --- Numerical Simulation Techniques for Studying Complex Nanostructures --- p.30
Chapter 2.3 --- Optical Force Calculation with the Maxwell Stress Tensor Method --- p.38
Chapter 2.4 --- Nanostructure Fabrication and Characterization --- p.40
Chapter Chapter 3. --- Optical Sensing Based on Double-Layered Metal Nano-Strips --- p.43
Chapter 3.1 --- Introduction --- p.43
Chapter 3.2 --- Theoretical Model and Analysis --- p.46
Chapter 3.3 --- Numerical Verification and Discussion --- p.50
Chapter 3.4 --- Optical Sensing Evaluation --- p.54
Chapter 3.5 --- Near-Field Modulation by Optically Trapped Metal Nanoparticles --- p.58
Chapter 3.6 --- Discussion --- p.61
Chapter 3.7 --- Conclusion --- p.62
Chapter Chapter 4. --- Gold Nano-Ring as Plasmonic Nano-Optical Tweezer --- p.64
Chapter 4.1 --- Introduction --- p.64
Chapter 4.2 --- Design and Optical Response --- p.67
Chapter 4.3 --- Optical Force Calculation and Evaluation of Trapping Performance --- p.73
Chapter 4.4 --- Stable Trapping Sites and Active Trapping Volume --- p.76
Chapter 4.5 --- Near-Field Variation and Discussion --- p.81
Chapter 4.6 --- Conclusion --- p.84
Chapter Chapter 5. --- Graded Plasmonic Nano-Disks for Near-Field Nano-Manipulation --- p.86
Chapter 5.1 --- Introduction --- p.86
Chapter 5.2 --- Modeling and Optical Response --- p.89
Chapter 5.3 --- Optical Force Distribution in the Structure --- p.91
Chapter 5.4 --- Optical Trapping Potential and Rotational Energy --- p.96
Chapter 5.5 --- Optical Trapping Volume and Discussion --- p.101
Chapter 5.6 --- Conclusion --- p.104
Chapter Chapter 6. --- Monitoring Plasmonic Nano-Optical Trapping through Detection of Surface-Enhanced Raman Scattering --- p.106
Chapter 6.1 --- Introduction --- p.106
Chapter 6.2 --- Numerical Investigation --- p.110
Chapter 6.3 --- Sample Preparation and Characterization --- p.112
Chapter 6.4 --- Experimental Implementation and Results --- p.122
Chapter 6.5 --- Discussion --- p.134
Chapter 6.6 --- Conclusion --- p.137
Chapter Chapter 7. --- Conclusion and Outlook --- p.139
References --- p.146
Publications from this Work --- p.171

基於局域表面等離子體共振極其敏感于金屬納米結構的尺寸和形貌的特性，貴金屬納米晶體在近些年來受到了研究人員的極大注意。而膠體金屬納米顆粒在共振時表現出極大的光散射和光吸收截面，且存在于金屬表面的電磁場強度也遠遠高於入射光的電磁場強度。膠體顆粒的各種應用已被發掘並廣泛應用於生物醫學領域，比如表面增強拉曼散射、表面增強螢光、基於等離子的傳感及光熱治療等。然而由於金材料的損耗係數大於銀，金納米材料對電磁場的增強效果弱于銀納米材料。傳統的銀納米膠體顆粒的局域表面等離子體共振峰多局限於420~500 nm，而常見的商業雷射器多在500~660 nm範圍內，目前對膠體銀納米顆粒的大小和形狀的可控性研究的報到還很有限，且將銀納米顆粒的共振調控到常用雷射器的波長範圍內對實際的應用有著重大的意義。本篇論文將系統地研究利用光化學方法製備銀納米十面體和相關納米結構，以及他們的等離子體增強效果。
首先，我們將介紹各種化學試劑及光源在銀納米顆粒的形成過程中的作用，以及一種能較好的控制銀納米十面體（LSPR：420~660 nm）的大小的方法。我們發現化學試劑和光源對最終納米顆粒的純度和形狀均有影響。比如通過調節硝酸銀和檸檬酸鈉的摩爾比例可以有效的控制被硼氫化鈉還原出來的金屬納米顆粒的晶體結構。465nm的光照能有效地將聚乙烯吡咯烷酮穩定的小金屬銀納米顆粒轉變成納米十面體。如果我們再使用與十面體種子顆粒的LSPR接近的LED作為光源，並用含有大量的金屬銀納米小顆粒溶液做為前驅液，更大的金屬納米十面體顆粒（LSPR：490~590 nm）可以獲得。而另一方面，使用通過離心的方法提純出來的銀十面體作為種子，更大範圍的金屬十面體（LSPR：490~660 nm）可以被生長出來，即使我們只使用了一種光源（500nm LED）。
之後，我們研究了銀十面體的光學性質，及它們基於表面增強拉曼散射的低濃度分子探測的應用。相比于其他形狀的金屬納米顆粒，銀納米十面體能得到更強的拉曼信號，這表明銀納米十面體對局域場的增強效果優於其他的顆粒。實驗結果表明，單個金屬納米顆粒的拉曼平均增強係數能達到10⁶。爲了能將銀納米十面體應用於生物傳感和成像領域，我們製備出具有高穩定性和強拉曼信號的表面增強拉曼探針。另一方面，通過表面增強拉曼光譜，銀納米十面體修飾的矽片能靈敏地探測出10⁻⁸ M的4-MBA分子。我們並通過模擬計算的方法證明，在十面體和襯底之間加入介質和導體薄膜能進一步增加其拉曼靈敏度。
最後，我們通過光化學方法在襯底上製備出金屬銀納米結構，並得到一些初步的實驗結果。在633nm鐳射的照射下，組裝在玻璃襯底上的小納米顆粒將會轉變由銀納米片組成的納米結構。通過測量，存在于金屬納米結構中的週期只有幾個微米，這也充分的表明通過光化學的方法，我們可以在襯底上製備出由銀納米顆粒組成的任意結構。拉曼光譜可以作為一種實時觀測銀納米結構生長和表面增強拉曼“熱點形成的有效手段。
Noble-metal nanocrystals have received considerable attention in recent years for their size and shape dependent localized surface Plasmon resonances (LSPR). Various applications based on colloidal nanoparticles, such as surface enhanced Raman scattering (SERS), surface enhanced fluorescence (SEF), plasmonic sensing, photothermal therapy etc., have been broadly explored in the field of biomedicine, because of their extremely large optical scattering and absorption cross sections, as well as giant electric field enhancement on their surface. However, despite its high chemical stability, gold exhibits quite large losses and electric field enhancement is comparatively weaker than silver. Silver nanoparticles synthesized by the traditional technique only cover an LSPR ranged from 420~500 nm. On the other hand, the range of 500~660 nm, which is covered by several easily available commercial laser lines, very limited colloidal silver nanostructures with controllable size and shape have been reported, and ealization of tuning the resonance to longer wavelengths is very important for the practical applications. In this thesis, a systematic study on photochemical synthesis of silver nanodecahedrons (NDs) and related nanostructures, and their plasmonic field enhancements are presented.
First, the roles of chemicals and the light source during the formation of silver nanoparticles have been studied. We have also developed a preparation route for the production size-controlled silver nanodecahedrons (LSPR range 420~660 nm) in high purity. Indeed our experiments indicate that both the chemicals and the light sources can affect the shape and purity of final products. Adjusting the molar ratio between sodium citrate and silver nitrate can help to control the crystal structure following rapid reduction from sodium borohydride. Light from a blue LED (465 nm) can efficiently transform the polyvinylpyrrolidone stabilized small silver nanoparticles into silver NDs through photo excitation. These silver NDs acting as seeds can be re-grown into larger silver NDs with LSPR ranging from 490 nm to 590 nm, upon receiving LED irradiation with emission close to the LSPR of silver ND seeds, which are suspended in a precursor solution containing small silver nanoparticles. With the aid of centrifugation, silver NDs with high purity can be obtained. Furthermore, silver ND with a broad tuning range (LSPR 490~660 nm) can be synthesized from these seeds using irradiation from a 500 nm LED.
Second, the optical properties of silver NDs and their SERS application for sensitive molecular detection are presented. Raman signal obtained from silver NDs show remarkable advantage over noble nanoparticles of other shaped, thus revealing their strong localized field enhancement. Experimental results demonstrate that average enhancement factor from individual silver ND may be as high as 10⁶. In order to explore their application for biosensing and bioimaging, stable silica coated SERS tags based on silver ND producing high Raman intensity have been studied. Our experiment results indicate that 10⁻⁸ M 4-MBA in solution can be detected by silver NDs modified silicon chip through SERS. Simulation result on the geometry of silver ND/silica spacer/gold film/substrate shows that the Raman sensitivity of the NDs modified chip can be further improved with the insertion of a dielectric/conductor film between them.
Finally, we present a photochemical method for the preparation of silver nanostructures preparation with the use of 633 nm laser. Silver nanostructures composed of silver nanoplates could be grown from small silver nanoparticles deposited on a glass substrate. The periodicity of the silver nanostructures is several micrometers, revealing that this photochemical method has the potential for “writing“ silver pattern on a solid substrate. Raman spectroscopy has also been explored for real-time monitoring of silver nanostructure growth and SERS hotspots formation.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Lu, Haifei.
"December 2012."
Thesis (Ph.D.)--Chinese University of Hong Kong, 2013.
Includes bibliographical references (leaves 122-140).
Abstract also in Chinese.
Chapter Chapter 1. --- Introduction --- p.1
Chapter 1.1 --- Chemical synthesis of noble nanoparticles --- p.1
Chapter 1.1.1 --- Nucleation --- p.4
Chapter 1.1.2 --- Evolution from Nuclei to Seeds --- p.5
Chapter 1.1.3 --- Evolution from Seeds to Nanocrystals --- p.9
Chapter 1.2 --- Theoretical background of localized surface plasmon (LSP) --- p.14
Chapter 1.2.1 --- Determination of the dielectric constant --- p.15
Chapter 1.2.2 --- Maxwell equations --- p.20
Chapter 1.2.3 --- Quasi static approximation --- p.21
Chapter 1.2.4 --- Gans Theory --- p.22
Chapter 1.2.5 --- Mie theory --- p.23
Chapter 1.2.6 --- Numerical methods --- p.25
Chapter 1.3 --- Structure of this thesis --- p.29
Chapter Chapter 2. --- Optical properties of noble nanoparticles and their biomedical applications --- p.30
Chapter 2.1 --- Introduction --- p.30
Chapter 2.2 --- LSPR of nanoparticles with different shapes and different material composition --- p.30
Chapter 2.4 --- Local field enhancement of nanoparticles and their effects to Raman and fluorescence --- p.35
Chapter 2.5 --- Noble nanoparticles for biomedical applications --- p.38
Chapter 2.5.1 --- Noble nanocrystals for diagnostics --- p.38
Chapter 2.5.2 --- Noble nanocrystals for cellular and in vivo bioimaging --- p.41
Chapter 2.5.3 --- Noble metal nanocrystals in medicine --- p.43
Chapter Chapter 3. --- Photochemical synthesis of size controlled silver nanodecahedrons (NDs) --- p.46
Chapter 3.1 --- Introduction --- p.46
Chapter 3.2 --- Seed mediated plasmon driven regrowth of silver nanodecahedrons . --- p.47
Chapter 3.3 --- Chemical roles of reagents in the process and mechanism for photogrowth of silver nanodecahedrons --- p.55
Chapter 3.4 --- Light wavelength effect to the regrowth of silver NDs --- p.63
Chapter 3.5 --- Control on the crystal defects of small silver nanoparticles and effect of precursor to the regrowth of various size silver NDs --- p.67
Chapter 3.6 --- Summary --- p.77
Chapter Chapter 4. --- SERS assessment of silver nanodecahedrons and their application for sensitive detection based on SERS --- p.78
Chapter 4.1 --- Introduction --- p.78
Chapter 4.2 --- Investigation on SERS of silver NDs and other nanoparticles --- p.79
Chapter 4.3 --- Silica coated SERS tags with silver NDs as the core --- p.85
Chapter 4.4 --- Silver nanodecahedrons for biosensing --- p.93
Chapter 4.5 --- Summary --- p.101
Chapter Chapter 5. --- Photochemical growth of Plasmonic nanostructures on solid substrate --- p.103
Chapter 5.1 --- Introduction --- p.103
Chapter 5.2 --- Experimental --- p.104
Chapter 5.3 --- Result and discussion --- p.105
Chapter 5.3.1 --- Photochemical growth of silver nanostructures by laser irradiation through a single slit --- p.105
Chapter 5.3.2 --- SERS characterization of silver nanostructures --- p.110
Chapter 5.3.3 --- Observation of photochemical growth of silver nanostructures --- p.112
Chapter 5.4 --- Summary --- p.115
Chapter Chapter 6. --- Conclusion and outlook --- p.117
References --- p.122

在本篇論文中，我們成功地在透明導電襯底上製備了一系列準一維納米材料陣列。我們首先製備了氧化鋅納米線陣列，然後把它們用作氧化鋅/硒化鎘核殼納米線纜陣列中的核以及合成硒化鎘和碲化鎘納米管陣列所需的犧牲模板。最後，金納米管陣列則是利用之前製備的硒化鎘納米管陣列為模板合成的。氧化鋅納米線陣列是通過高溫的熱蒸法和低溫的水熱法製備的。水熱法製備的氧化鋅納米線陣列的電導高於熱蒸法製備的氧化鋅納米線陣列，這使得水熱法製備的氧化鋅納米線更適合採用與電相關的後續處理方法。當氧化鋅納米線陣列被用作犧牲模板來製備納米管時，水熱法製備的氧化鋅納米線能被輕易地完全去除。基於這些認識，我們主要採用電化學沉積法在水熱法製備的氧化鋅納米線陣列表面沉積硒化鎘，得到了氧化鋅/硒化鎘核殼納米線纜陣列。接下來，我們將納米線纜陣列光電極和沉積了鉑催化劑的對電極組裝成三文治結構的太陽能電池。研究發現，採用多硫電解液的電池性能比碘基電解液的電池好，其中成分為1摩爾每升硫化鈉，1摩爾每升硫和1摩爾每升氫氧化鈉的多硫電解液的電池效率最高。當去除電化學沉積法生長的氧化鋅/硒化鎘和氧化鋅/碲化鎘核殼納米線纜陣列中的氧化鋅核以後，便在導電襯底上得到了硒化鎘和碲化鎘的納米管陣列。儘管兩種納米管陣列都對可見光有很強的吸收，但是，硒化鎘納米管陣列相比碲化鎘納米管陣列，表現出較高的光響應和較好的光催化降解亞甲基藍的活性。這是因為該樣品中的光生載流子能有效分離，同時能參與化學反應的表面積也較大。最後，我們選用硒化鎘納米管陣列作為模板，利用化學方法製備了金納米管陣列。金納米管的尺寸可以通過控制硒化鎘納米管模板來加以調節。當我們將具有拉曼活性的4-巰基苯甲酸分子吸附到金納米管的表面時，其拉曼散射相比未吸附時，顯著地增強了約四個數量級，如此大的提高來源於金納米管表面附近的局域電場增強效應。
In this thesis, we demonstrated the synthesis of a series of pseudo-one-dimensional nanostructure arrays on transparent conducting substrates. We started with ZnO nanowire arrays, which were then served as the core for the ZnO/CdSe core/shell nanocable arrays formation. Further taking the ZnO as sacrificial templates led to the formation of CdSe (and CdTe) nanotube arrays. Finally, Au nanotube arrays were fabricated using the CdSe nanotube arrays as the template. ZnO nanowire arrays were synthesized via high-temperature thermal evaporation method (TE) and low temperature hydrothermal method (HT). The electrical conductivity of HT samples on the substrates was higher than that of the TE counterparts, making it attractive for further electrical-based processing. When serving as the sacrificial templates for nanotube fabrication, HT nanowires can be completely removed with ease. Based on these understanding, ZnO/CdSe core/shell nanocable arrays were obtained mainly via electrochemical deposition of CdSe on HT ZnO nanowire arrays. Nanocable-array-photoelectrode was assembled with a Pt-coated counter electrode into a sandwiched solar cell. Polysulfide electrolytes with various compositions were found to work better than iodine-based ones for such cells, and the cell with the polysulfide electrolyte containing 1 M Na₂S, 1 M S and 1 M NaOH showed highest efficiency. Removal of the ZnO cores in the electrodeposited ZnO/CdSe and ZnO/CdTe nanocable arrays left CdSe and CdTe nanotube arrays on the conducting substrate. Although strong visible-light absorption was observed from both two nanotube arrays, higher photocurrent and better photocatalytic degradation activity of methlyene blue were recorded from CdSe-nanotube-array samples (as compared to the CdTe ones), owing to effective charge separation and large surface area for chemical reactions. Lastly, Au nanotube arrays were synthesized via chemical method using CdSe nanotube arrays as the template. The dimensions of the Au nanotubes, as replicated from CdSe nanotubes, were tunable. When absorbed on the Au nanotube arrays surface, the Raman scattering of 4-mercaptobenzoic acid (a Raman-active molecule) was greatly enhanced for~4 orders of magnitude compared to the signals from the dry powder of the same molecule. Such large increase was due to the strong local electrical field enhancement near the Au nanotubes surface.
Detailed summary in vernacular field only.
Zhu, Haojun = 準一維納米結構在光伏、光催化及等離子體激元方面的應用 / 朱浩君.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2012.
Includes bibliographical references (leaves 141-168).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.
Abstracts in English and Chinese.
Zhu, Haojun = Zhun yi wei na mi jie gou zai guang fu, guang cui hua ji deng li zi ti ji yuan fang mian de ying yong / Zhu Haojun.
Abstract --- p.i
摘要 --- p.iii
Acknowledgements --- p.iv
Contents --- p.v
List of Figures --- p.viii
List of Tables --- p.xviii
Chapter Chapter 1 --- Introductions --- p.1
Chapter Chapter 2 --- Background --- p.4
Chapter 2.1. --- Nanostructured Photovoltaic (PV) Solar Cells --- p.4
Chapter 2.1.1. --- Fundamental physics of nanostructures for solar cell applications --- p.5
Chapter 2.1.2. --- Inorganic nano-architectures for PV cells --- p.9
Chapter 2.2. --- Nanostructures for Photocatalytic Degradation of Organic Pollutants --- p.18
Chapter 2.2.1 --- Overview of photocatalytic degradation of organic pollutants --- p.19
Chapter 2.2.2 --- Photocatalysis under visible light illumination --- p.24
Chapter 2.3. --- Plamonic Noble Metal Nanostructures --- p.29
Chapter 2.3.1 --- Surface plasmons of noble metal nanostructures --- p.29
Chapter 2.3.2 --- Applications of plasmonic noble metal nanostructures in solar energy conversion and sensing --- p.35
Chapter Chapter 3 --- Methodologies and Instrumentations --- p.45
Chapter 3.1. --- Materials Growth Methodologies --- p.45
Chapter 3.1.1. --- Thermal evaporation (TE) methods --- p.45
Chapter 3.1.2. --- Hydrothermal (HT) methods --- p.47
Chapter 3.1.3. --- Electrodeposition (ED) methods --- p.49
Chapter 3.1.4. --- Prototype solar cells assemble --- p.52
Chapter 3.2. --- Characterization Techniques --- p.53
Chapter 3.2.1. --- Morphological, structural, and compositional analysis using electron microscopy based techniques --- p.53
Chapter 3.2.2. --- Photoelectrochemical (PEC) performance test --- p.63
Chapter 3.2.3. --- Photocatalytic degradation of organic pollutants --- p.65
Chapter 3.2.4. --- Single-particle scattering imaging and spectroscopy --- p.67
Chapter Chapter 4 --- ZnO Nanowire Arrays on Conducting Substrates -- A Comparison on the Growth Methodology --- p.71
Chapter 4.1. --- Introduction --- p.71
Chapter 4.2. --- Experimental --- p.72
Chapter 4.3. --- Results and Discussions --- p.75
Chapter 4.3.1 --- Morphologies, crystal structures and chemical compositions --- p.75
Chapter 4.3.2 --- ZnO nanowire arrays used as electrodes --- p.80
Chapter 4.3.3 --- ZnO nanowire arrays used as sacrificial templates in electroplating . --- p.85
Chapter 4.4. --- Conclusions --- p.88
Chapter Chapter 5 --- ZnO-core/CdSe-shell Nanocable Arrays for Photovoltaic Solar Cells --- p.89
Chapter 5.1. --- Introduction --- p.89
Chapter 5.2. --- Experimental --- p.90
Chapter 5.3. --- Results and Discussions --- p.93
Chapter 5.3.1 --- Synthesis of the ZnO-core/CdSe-shell nanocable arrays on ITO/glass --- p.93
Chapter 5.3.2 --- The photovoltaic (PV) performance --- p.100
Chapter 5.4. --- Conclusions --- p.107
Chapter Chapter 6 --- CdSe and CdTe Nanotube Arrays as Visible-light-driven Photocatalyst for Organic Pollutant Degradation --- p.108
Chapter 6.1. --- Introduction --- p.108
Chapter 6.2. --- Experimental --- p.109
Chapter 6.3. --- Results and Discussions --- p.112
Chapter 6.3.1. --- Morphology, crystal structure, and chemical composition of the nanotube arrays --- p.112
Chapter 6.3.2. --- Optical properties --- p.116
Chapter 6.3.3. --- Photoelectrochemical (PEC) performance --- p.117
Chapter 6.3.4. --- Photocatalytic activities --- p.120
Chapter 6.4. --- Conclusions --- p.123
Chapter Chapter 7 --- Fabrication of Au Nanotube Arrays and Their Plasmonic Properties --- p.124
Chapter 7.1. --- Introduction --- p.124
Chapter 7.2. --- Experimental --- p.125
Chapter 7.3. --- Results and Discussions --- p.127
Chapter 7.3.1. --- Morphology, crystalline structure, and chemical composition of Au nanotube arrays --- p.127
Chapter 7.3.2. --- Au nanotube formation mechanism --- p.129
Chapter 7.3.3. --- Plasmonic properties of Au nanotube arrays on ITO/glass substrates --- p.131
Chapter 7.3.4. --- Plasmonic properties of single Au nanotubes --- p.133
Chapter 7.3.5. --- Au nanotube arrays on ITO/glass as SERS substrates --- p.134
Chapter 7.4. --- Conclusions --- p.138
Chapter Chapter 8 --- Conclusions --- p.139
Bibliography --- p.141

表面等離子體基元共振是自由電子在納米尺寸的集體共振效應，該效應會產生一系列新奇的性質。貴金屬納米結構由於可以產生表面等離子體基元共振而受到各個領域廣泛的關注。在共振激發的情況下，貴金屬納米結構具有極大的散射和吸收截面積以及極強的進場放大效應。這些奇特的性質可以應用於傳感、成像、光學調製、光熱療、光催化和太陽能電池等領域。金和銀納米結構由於其表面等離子體基元共振波長處在可見和近紅外波段而受到廣泛研究。然而，在某些應用中純金或純銀納米結構不能起到很好的作用。例如，金和銀對很多化學反應的催化活性很弱或者沒有催化活性。如果把金和銀與其他金屬複合在一起就可以同時獲得表面等離子基元共振和其他效應。在我的博士研究期間，我製備了Au/Ag 和Au/Pd 複合雙金屬納米結構和研究了該複合結構的表面等離子體基元共振的性質和在氫氣傳感和光催化中的應用。
由於在金屬納米結構的製備中晶種起著至關重要的作用，所以我首先研究了晶種的晶體結構和形狀對雙金屬納米結構合成的影響。我研究了銀和鈀分別在相同條件下在單晶金納米棒、多晶金納米棒和納米雙錐種子上的生長過程。研究發現當晶種是單晶金納米棒時，銀和鈀的生長形成長方體雙金屬納米結構。然而，當晶種是多晶的金納米棒和納米雙錐時，銀和鈀的生長生成納米棒雙金屬結構。銀和鈀在多晶金納米棒上的生長由兩端開始，而在多晶金納米雙錐上的生長由臺階面開始。這表明在雙金屬納米結構的生長過程中納米晶種的晶體結構對最終納米結構的形貌具有決定性的作用，而納米晶種的形狀對生長動力學有明顯的影響。
在Au/Ag納米晶製備過程中，我發現Au/Ag納米晶具有四個表面等離子體基元共振峰。於是我對這四個共振峰的演變和共振模式進行了實驗和理論研究。電動力學模擬表明能量最低的共振峰是縱向的電偶極共振，能量次低的共振峰是沿橫向的電偶極共振，兩個高能量的共振峰是沿著橫向的電八極共振。遲滯效應和兩個垂直橫向激發的干涉是導致形成兩個電八極共振的關鍵因素。研究發現隨著銀殼厚度的增加，縱向電偶極共振峰藍移，橫向電偶極共振峰先藍移后稍微紅移，兩個電八極共振沒有明顯的峰位移動。四個表面等離子體基元共振的強度都隨著銀殼厚度的增加而增強。
鈀被廣泛地應用於氫氣傳感和催化反應中。於是我研究了Au/Pd 雙金屬納米結構的氫氣傳感和光催化性能。在氫氣傳感研究中，我製備了兩種不同結構的Au/Pd 納米結構。一種具有連續的鈀殼層，另一種鈀殼層不連續。對於具有連續鈀殼層的納米結構，氫氣的傳感性能隨著鈀殼層厚度的增加而增加。實驗發現當納米結構暴露在4%的氫氣中時表面等離子體基元共振峰移動高達56 nm。不連續鈀殼層的納米結構的氫氣傳感性能不如連續鈀層的納米結構。我進一步對Au/Pd 雙金屬納米結構的光催化性能進行了研究。所選取的催化反應是Suzuki 偶聯反應。研究結果表明Au/Pd 納米結構可以有效地捕獲光能來促進化學反應。由於Au/Pd 納米結構使表面等離子體基元共振功能和催化功能緊密集成在一個納米結構中，因此表面等離子基元共振部份所捕獲的光能可以有效地傳遞到催化功能部份而實現光催化。研究發現熱電子效應和光熱轉化效應同時加速化學反應。其中光熱轉化在我的實驗中體現為非局部加熱效應，熱電子對化學反應的促進作用依賴于環境溫度。因此，光熱轉化效應可以促進熱電子轉移效應。
本論文的研究結果有助於人們瞭解具有表面等離子體基元共振性質的雙金屬納米機構的設計和應用。對Au/Ag雙金屬納米結構表面等離子體基元共振性質的研究不僅加深了人們對雙金屬表面等離子體基元共振的瞭解而且對利用不同共振模式實現特定功能有著指導意義。對Au/Pd雙金屬納米結構在氫氣傳感和催化反應應用中的研究明確表面雙金屬表面等離子體納米結構可以實現單一組成不具備的功能，這在一定程度上有助於擴展表面等離子基元共振在生命科學、能源和環境領域的應用。
Noble metal nanocrystals have attracted great interest from a wide range of research fields because of their intriguing properties endowed by their localized surface plasmon resonances, which are the collective oscillations of free electrons. Under resonant excitation, metal nanostructures exhibit very large scattering and absorption cross sections and large near-field enhancement. These extraordinary properties can be used in different applications, such as plasmonic sensing and imaging, plasmon-controlled optics, photothermal therapy, photocatalysis, solar cells, and so on. Gold and Silver nanocrystals have plasmon resonances in the visible and near-infrared regions. However, gold and silver are not suitable for some applications. For example, they are generally inactive for catalyzing chemical reactions. The integration of plasmonic metals with other metals can offer superior or new physical/chemical properties. In this thesis, I prepared Au/Ag and Au/Pd bimetallic nanostructures and studied their lasmonic properties and applications in hydrogen sensing and photocatalysis.
Seeds have a crucial importance in the synthesis of bimetallic nanostructures. I therefore first studied the roles of the crystalline structure and shape of seeds on the overgrowth of bimetallic nanostructures. The overgrowth of silver and palladium on single crystalline Au nanorods, multicrystalline Au nanorods, and nanobipyramids were studied under the same conditions for each metal. The growths of silver and palladium on single crystalline Au nanorods gave cuboidal nanostructures, while rod-shaped nanostructures were obtained from the growths of silver and palladium on multicrystalline Au nanorods and nanobipyramids. Moreover, the growths of silver and palladium on multicrystalline Au nanobipyramids started at the stepped side facets, while the growths started at the twin boundaries on multicrystalline Au nanorods. These results unambiguously indicate that the crystalline structure of seeds plays a significant role on the final morphologies of multimetallic nanostructures, while the seed shape has a prominent effect on the growth kinetics.
Four plasmon resonance bands were observed in Au/Ag bimetallic nanocrystals. I then studied the evolution and nature of the four plasmon bands during the silver coating on Au nanorods both experimentally and theoretically. Electrodynamic simulations revealed that the lowest-energy peak belongs to the longitudinal dipolar plasmon mode, the second-lowest-energy peak is the transverse dipolar plasmon mode, and the two highest-energy peaks can be attributed to octupolar plasmon modes. The retardation effect and the interference between two perpendicularly polarized excitations along the edge directions are important for the formation of the distinct highest-energy and second-highest-energy octupolar plasmon modes, respectively. As the Ag shell thickness is increased, the longitudinal plasmon mode blue-shifts, the transverse plasmon mode first blue-shifts and then red-shifts slightly, and the two octupolar plasmon modes stay at nearly constant wavelengths. The extinction intensities of all the four plasmon bands increase with the increase of the overall particle size.
Palladium is widely used in hydrogen sensing and catalysis. I therefore studied the applications of Au/Pd bimetallic nanostructures in hydrogen sensing and photocatalysis. Two types of Au/Pd bimetallic nanostructures, nanostructures with continuous and discontinuous Pd shells, were employed to study their hydrogen sensing performances. For the nanostructures with continuous Pd shell, the hydrogen sensing performances were improved with the increase in the Pd shell thickness. A plasmon shift of 56 nm was observed when the hydrogen concentration was 4%. The nanostructures with discontinuous Pd shell exhibited smaller plasmon shifts compared with those with continuous Pd shell. For the photocatalytic application of Au/Pd bimetallic nanostructures, I studied their photocatalytic performance for Suzuki coupling reactions. The results indicate that plasmonic Au/Pd bimetallic nanostructures can efficiently harvest light energy for chemical reactions. The intimate integration of plasmonic and catalytic components in one nanostructure enables the light energy absorbed by the plasmonic component to be directly transferred to the catalytic component. Both hot electron transfer and photothermal heating contribute to the plasmon-enhanced chemical reactions. The photothermal effect is a nonlocal heating and the contribution of the hot electron transfer effect is dependent on the environmental temperature. Therefore, the photothermal heating effect can promote the hot electron transfer effect.
I believe that my research work will be very helpful for the design and application of plasmonic bimetallic nanostructures. My study on the plasmonic properties of Au/Ag bimetallic nanocrystals has deepened the understanding of the plasmons of Au/Ag nanorods and will be helpful for utilizing the different modes to achieve specific functions. The hydrogen sensing and photocatalysis of Au/Pd bimetallic nanostructures have shown that the integration of functional components with plasmonic nanostructures can achieve unconventional properties, which will flourish the applications of plasmons in life sciences, energy, and environmental areas.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Jiang, Ruibin = 雙金屬納米結構表面等離子體基元共振的研究及其在氫氣傳感和化學反應中的應用 / 江瑞斌.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2013.
Includes bibliographical references.
Abstracts also in Chinese.
Jiang, Ruibin = Shuang jin shu na mi jie gou biao mian deng li zi ti ji yuan gong zhen de yan jiu ji qi zai qing qi chuan gan he hua xue fan ying zhong de ying yong / Jiang Ruibin.
Abstract --- p.I
Acknowledgements --- p.VI
Table of Contents --- p.VIII
List of Figures --- p.X
List of Tables --- p.XIII
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Localized surface plasmon resonances --- p.1
Chapter 1.2 --- Applications of localized surface plasmon resonances --- p.3
Chapter 1.3 --- Overview of this thesis --- p.13
Chapter 2 --- Theory, Simulation, and Experimental Methods for the Investigation of LSPRs --- p.20
Chapter 2.1 --- Theoretical methods --- p.20
Chapter 2.2 --- Simulation methods --- p.30
Chapter 2.3 --- Experimental methods --- p.35
Chapter 3 --- Preparation of Metal Nanostructures --- p.43
Chapter 3.1 --- Preparation methods for Au nanocrystals --- p.43
Chapter 3.2 --- Seed-mediated growth method --- p.46
Chapter 3.3 --- Metal nanostructure preparations --- p.54
Chapter 4 --- Crystalline Structure-Determined Growth of Bimetallic Nanocrystals --- p.62
Chapter 4.1 --- Au nanocrystal seed preparation --- p.64
Chapter 4.2 --- Au/Ag bimetallic nanocrystals --- p.66
Chapter 4.3 --- Au/Pd bimetallic nanocrystals --- p.71
Chapter 4.4 --- Summary --- p.77
Chapter 5 --- Plasmons of Au/Ag Core/Shell Bimetallic Nanocrystals --- p.83
Chapter 5.1 --- Variations of plasmons with Ag shell thickness --- p.86
Chapter 5.2 --- Nature of the different plasmon modes --- p.94
Chapter 5.3 --- Summary --- p.99
Chapter 6 --- Au/Pd Bimetallic Nanostructures for Hydrogen Sensing --- p.105
Chapter 6.1 --- Au nanorods with continuous Pd shell for hydrogen sensing --- p.107
Chapter 6.2 --- Au nanorods with discontinuous Pd shell for hydrogen sensing --- p.114
Chapter 6.3 --- Theoretical simulations --- p.117
Chapter 6.4 --- Summary --- p.119
Chapter 7 --- Plasmon-Enhanced Chemical Reactions --- p.124
Chapter 7.1 --- Mechanisms of plasmon enhancement in chemical reactions --- p.125
Chapter 7.2 --- Plasmon-enhanced Suzuki coupling reactions --- p.129
Chapter 7.3 --- Summary --- p.149
Chapter 8 --- Conclusions --- p.156
Curriculum Vita --- p.160

DNA origami is a novel self-assembly technique that can be used to form various

2D and 3D objects, and to position matter with nanometer accuracy. It has been

used to coordinate the placement of nanoscale objects, both organic and inorganic, to make molecular motor and walkers; and to create optically active nanostructures. In this dissertation, DNA origami templates are used to assemble plasmonic structures. Specifically, engineered Surface Enhanced Raman Scattering (SERS) substrates were fabricated. Gold nanoparticles were selectively placed on the corners of rectangular origami and subsequently enlarged via solution-based metal deposition. The resulting assemblies exhibited "hot spots" of enhanced electromagnetic field between the nanoparticles. These hot spots significantly enhanced the Raman signal from Raman molecules covalently attached to the assemblies. Control samples with only one nanoparticle per DNA template, which therefore lacked inter-particle hot spots, did not exhibit strong enhancement. Furthermore, Raman molecules were used to map out the hot spots' distribution, as the molecules are photo-damaged when experiencing a threshold electric field. This method opens up the prospect of using DNA origami to rationally engineer and assemble plasmonic structures for molecular spectroscopy.

Dissertation

了解表面等子體和外部環境之間的相互作用對表面等子體應用的開發非常重要。我們的研究集中在表面等子體與遠場的耦合，以及表面等子體模之間的耦合。
首先，我們研究由表面等子體模式耦合所產生的射衰變的變化。我們以角分辨反射光譜測同孔大小的納米孔陣上的簡併表面等子體模的衰減。對於每個孔的大小，我們觀察到在發生共振耦合的光譜區，衰減速有很大的改變，顯示出暗模和模的形成。耦合模很好地解釋衰變的變化。推導出的耦合常隨著孔直徑的增加而增加。我們也對耦合模一些有趣的特性及衰減變化的微觀起源進探討。
第二，我們以偏振分辨反射光譜從二維屬陣射散射。我們發現，反射光譜遵循的法模型可以由耦合模和瓊斯矩陣演算推導出。通過用正交方向的偏光器和分析器，反射光譜上的谷翻轉成峰，從以能夠測定出射散射效。我們發現，射散射效與波長和孔直徑的依賴關係和單孔的瑞散射相符合。
最後，我們開發一個新的方法，以偏振分辨光譜在實驗中測射衰變。這方法的有效性通過時域有限差分計算得到證明。我們還將此方法應用在實驗據上作為示範。
Understanding the interaction between surface plasmon and outer environment is crucial in development of plasmonic applications. Our study is focused on the coupling between surface plasmons and far field, and also the coupling between surface plasmon modes.
First, we studied the change in radiative decay rate due to coupling of degenerate surface plasmon modes. We measured the decay rates of two degenerate surface plasmon modes in Au nanohole arrays with different hole sizes by angle-resolved reflectivity spectroscopy. For each hole size, at the spectral region where resonant coupling occurs, we observed a large modification in decay rates, leading to the formation of dark and bright modes. The change in decay rates is well explained by coupled-mode theory. The deduced coupling constant is found to increase with increasing hole diameter. Interesting properties of the coupled modes and microscopic origin of the change in decay rate is also discussed.
Second, we measured the radiative scattering from two-dimensional metallic arrays by using polarization-resolved reflectivity spectroscopy. We found that the reflectivity spectra follow the Fano-like model which can be derived from coupled-mode theory and Jones matrix calculus. By orthogonally orienting the incident polarizer and the detection analyzer, reflectivity dips flip into peaks and the radiative scattering efficiency can be determined accordingly. The dependence of total radiative scattering efficiency on wavelength and hole diameter is found to agree well with Rayleigh scattering by single hole.
Finally, we developed a new method to measure radiative decay rates experimentally by polarization-resolved reflectivity spectroscopy. The validity of this method is proved by finite-difference time-domain simulation. We also applied this method on experimental data as a demonstration.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Lo, Hau Yung = 表面等離子體在金屬納米孔陣列的輻射衰減及耦合 / 羅孝勇.
"December 2012."
Thesis (M.Phil.)--Chinese University of Hong Kong, 2013.
Includes bibliographical references (leaves 88-92).
Abstracts also in Chinese.
Lo, Hau Yung = Biao mian deng li zi ti zai jin shu na mi kong zhen lie de fu she shuai jian ji ou he / Luo Xiaoyong.
Chapter 1 --- Introduction --- p.1
Chapter 2 --- Basic Theory and Techniques --- p.3
Chapter 2.1 --- Macroscopic Maxwell Equations and Boundary Conditions --- p.3
Chapter 2.2 --- Symmetries and Band Structure --- p.4
Chapter 2.3 --- Coupled-mode Theory --- p.10
Chapter 2.4 --- Finite-difference Time-domain Simulation --- p.12
Chapter 2.5 --- Preparation of Metallic Nano-hole Arrays --- p.14
Chapter 3 --- Fundamentals of Surface Plasmons on Metallic Nanohole Array --- p.18
Chapter 3.1 --- Confinement and Propagation Nature of SPs --- p.18
Chapter 3.2 --- Skin Depth and Propagation Length --- p.19
Chapter 3.3 --- Dispersion Relation and Phase-matching Conditions --- p.21
Chapter 3.4 --- Measurement of Band Structure: Angle-resolved Reflectivity Mapping --- p.23
Chapter 3.5 --- Red Shift of Band Structure --- p.26
Chapter 3.6 --- Comparison of Two Presentations of Band Structure: "ω against k" versus "λ against θ" --- p.28
Chapter 3.7 --- Resonance Peak Shape: FanoModel and Wood's Anomalus --- p.30
Chapter 3.8 --- Resonance Peak Shape: "Fano-like" Model --- p.34
Chapter 3.9 --- Appendix A: Derivation of Eq(3.1) --- p.36
Chapter 4 --- Decay Rates Modification though Coupling of Degenerate Surface Plasmon modes --- p.40
Chapter 4.1 --- Introduction --- p.40
Chapter 4.2 --- Measurements of Degenerate Surface Plasmon Modes --- p.42
Chapter 4.3 --- Decay rates of Coupled Modes --- p.45
Chapter 4.4 --- Hole Diameter Dependence of Coupling Constants --- p.47
Chapter 4.5 --- Understanding the S-polarized Surface Plasmon Modes --- p.50
Chapter 4.6 --- TE-like Surface Plasmon Modes --- p.53
Chapter 4.7 --- Microscopic Origin of the Modification in Decay Rate --- p.54
Chapter 4.8 --- Summary --- p.60
Chapter 5 --- Direct Measurement of Radiative Scattering of Surface Plasmon Resonance from Metallic Arrays by Polarization-resolved Reflectivity Spectroscopy --- p.61
Chapter 5.1 --- Introduction --- p.61
Chapter 5.2 --- Theory of Direct Measurement of Radiative Scattering --- p.62
Chapter 5.3 --- Comparison with Experiment --- p.65
Chapter 5.4 --- Comparison with Rayleigh Scattering Model --- p.71
Chapter 5.5 --- Summary --- p.74
Chapter 6 --- A Method of Obtaining Radiative Decay Rates From Experiment --- p.76
Chapter 6.1 --- Introduction --- p.76
Chapter 6.2 --- Method --- p.77
Chapter 6.3 --- Prove of Validity --- p.78
Chapter 6.4 --- Experimental Demonstration --- p.82
Chapter 6.5 --- Summary --- p.85
Chapter 7 --- Conclusion --- p.86
Chapter 8 --- Bibliography --- p.88
Chapter 9 --- Curriculum Vitae --- p.93

Strongly coupled plasmon-exciton hybrid nanostructures are fabricated and their optical properties are studied. The plasmonic and excitonic systems are gold nanoshells and J-aggregates, respectively. Gold nanoshells are tunable plasmonic core-shell nanoparticles which can sustain distinct dipole and quadrupole plasmons with resonant energies dependent on core-size/shell-thickness ratio. J-aggregates are organic semiconducting material with excitons that possess very high oscillator strength making them suitable for coherent interaction with other kinds of excitations. The J-aggregates are formed on the surface of the nanoshells when a water/ethanol (50:50) solution of the dye molecules (2,2'-dimethyl-8-phenyl-5,6,5',6'-dibenzothiacarbocyanine chloride) is added to an aqueous solution of nanoshells. These nanoshell-J-aggregate complexes exhibit coherent coupling between localized plasmons of the nanoshell and excitons of the molecular J-aggregates. Coherent coupling strengths of 120 meV and 100 meV have been measured for dipole and quadrupole plasmon interactions with excitons, respectively. Femtosecond time-resolved transmission spectroscopy studies are carried out in order to understand the possible sources of optical nonlinearities in the nanoshell-J-aggregate hybrid. Transient absorption of the interacting plasmon-exciton system is observed, in dramatic contrast to the photoinduced transmission of the pristine J-aggregate. An additional, transient Fano-shaped modulation within the Fano dip is also observable. The transient behavior of the J-aggregate-Au nanoshell complex is described by a combined one-exciton and two-exciton state model coupled to the nanoshell plasmon.

由於表面等離子體激元可以將電磁場限制在金屬表面，從而產生強烈的場強增強效果，因此在納米光子學和生物光子學方面具有廣泛的應用價值，其中包括高性能發光二級管、光伏電池、超高分辨率光學成像和超靈敏分子檢測等。尤其在單分子和醫學診斷方面，基於表面等離子體共振的生物傳感器獲得了越來越多的青睞。本論文包括兩部份。第一部份著重討論二維週期性洞陣列的表面等離子體特性，而第二部份則是研究這種洞陣列結構在表面等離子體共振傳感方面的應用。
在第一部份中，表面等離子體模式被分為非簡並模式(m，O) 和簡並模式(m，±n)兩種情況分別加以討論。首先，結合實驗結果和理論模型，我們對非簡並模式的衰減壽命和激發效率進行了研究。通過光干涉光刻法和薄膜沉積技術，一系列不同幾何結構的洞陣列樣品被製備出來，且這些樣品具有很高的重複性。利用角分辨色散關係進行模式識別以及確定這些模式的衰減壽命和激發效率。通過調整起偏器和檢偏器的相對方向，表面等離子體模式的非輻射和輻射衰竭均可加以研究。結果發現，衰減壽命強烈依賴於單洞的幾何結構，而且這種行為可以用簡單的靜電模型并考慮高階修正加以解釋。從非輻射衰減和輻射衰減平衡的角度出發，激發效率對幾何結構和共振波長的依賴性也可以理解。對於簡并模式，由於存在稱合，對稱模式和反對稱模式分別被p 偏振激發和S偏振激發。它們的對稱性和對於衰減壽命和共振波長的修正可以用干涉法和模式耦合理論來理解。最後，利用多模耦合方程，我們對色散關係圖譜隨著洞深度增加而演化的情況也進行了探討。
第二部份對基於表面等離子體共振的生物傳感器與陣列幾何結構的關係進行了研究。結果發現，激發效率和衰減壽命對表面等離子體共振傳感器的分辨率都起到了關鍵性作用。在共振中，峰值高度和帶寬主要由表面等離子體的衰減速率控制。較低的衰減速率導致較清晰的峰值線型，從而產生較高的傳感器分辨率。因此，通過調整陣列的幾何結構以產生非常低得輻射衰減速率，表面等離于體共振傳感器的品質因數可高達104.8/RIU ，這已經超過了基於梭鏡和納米粒子對應器件的性能表現。
Surface plasmon polaritons (SPPs) generate a strong localized electromagnetic field on metal surface and thus are promising for nano- and bio-photonics including high performing light-emitting diodes and photovoltaic cells, super-high resolution optical imaging, ultra-high sensitive bimolecular detection, etc. In particular, the application of SPPs on surface plasmon resonance (SPR) biosensor has drawn much more attention recently because of the attempt to realize single molecule detection in medical diagnosis.
This thesis contains two parts. The first part focuses on studying the basic plasmonic properties of two-dimensional periodic hole arrays while the second part concentrates on the application of hole arrays on SPR sensing.
In the first part, SPPs modes on hole arrays are classified into nondegenerate mode (m, 0) and degenerate mode (m, ±n). For nondegenerate mode, its decay lifetime and generation efficiency are studied both experimentally and theoretically. By combining interference lithography and thin film deposition, a set of arrays with a wide range of geometry has been fabricated with high reproducibility. The dispersion relations of arrays are studied by angle-dependent reflectivity for mode identification and detenninations of SPP decay lifetime and generation efficiency. In particular, through orienting the polarization of the specular reflection either parallel or orthogonal to that of the incidence, we can access both the nonradiative and radiative decays of SPPs at different resonance wavelengths. As a result, it is found that decay lifetime is strongly dependent on the geometry of single hole and its behaviors can be understood by using a simple quasi-static model taking into account of the higher order correction as well as numerical simulation deduced by finite-difference timedomain. The dependence of generation efficiency on hole geometry or resonance wavelength can be understood in tenns of trade-off between nonradiative and radiative decay rates. Once these two decay rates equals to each other, the optimum generation efficiency is realized and the field enhancement gets the maximum. And the optimum parameters can be achieved by adjusting the hole geometry or the resonance wavelength. For degenerate mode, due to the coupling between (m, +n) and (m, -n) modes, a symmetric and an anti-symmetric modes are excited under pand s-polarized excitation, respectively. Their symmetries and modifications to the decay lifetime and resonance wavelength can be understood by using the interference method and coupled mode theory. Finally, generalized coupled mode equations are employed to know about the evolution of dispersion relation as hole depth increases.
The dependence of SPR biosensor on the generation and decay of SPPs are studied in the second part. Both the generation efficiency and decay lifetime of SPPs are found to be critical in governing the resolution of SPR biosensor. In SPR, the peak height and linewidth are primarily controlled by the decay rate of SPPs. Lower decay rate leads to sharper peak profile, which results in higher SPR resolution. Therefore, by tailoring the geometry of hole arrays to achieve a very low radiative decay rate, a SPR biosensor with figure of merit (FOM) reaching l04.8/RIU can be realized, which surpasses those of prism and nanoparticle counterparts.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Zhang, Lei = 表面等離子體激元對於週期性金屬納米結構幾何形狀的依賴性及其在生物傳感中的應用 / 張磊.
"November 2011."
Thesis (Ph.D.)--Chinese University of Hong Kong, 2012.
Includes bibliographical references (leaves 116-125).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.
Zhang, Lei = Biao mian deng li zi ti ji yuan dui yu zhou qi xing jin shu na mi jie gou ji he xing zhuang de yi lai xing ji qi zai sheng wu chuan gan zhong de ying yong / Zhang Lei.
Chapter Chapter1 --- Introduction --- p.1
Chapter Chapter2 --- Theoretical Background --- p.7
Chapter 2.1 --- Maxwell's equations --- p.7
Chapter 2.2 --- Classic electromagnetic theory for dielectric properties of matter --- p.9
Chapter 2.3 --- Surface plasmon polaritons at the dielectric/metal interface --- p.11
Chapter 2.4 --- Excitation of surface plasmon polaritons --- p.16
Chapter 2.4.1 --- Prism coupling --- p.17
Chapter 2.4.2 --- Grating coupling --- p.17
Chapter 2.5 --- lones calculus --- p.19
Chapter 2.6 --- Finite-difference time-domain method --- p.22
Chapter Chapter 3 --- Sample Preparation --- p.25
Chapter 3.1 --- Interference lithography --- p.25
Chapter 3.1.1 --- Substrate preparation --- p.26
Chapter 3.1.2 --- Exposure --- p.27
Chapter 3.1.3 --- Pattern development --- p.30
Chapter 3.2 --- Thin film deposition --- p.30
Chapter Chapter 4 --- Experimental Setups and Calibration --- p.33
Chapter 4.1 --- Experimental setup for measuring dispersion relation --- p.33
Chapter 4.2 --- Experimental setup calibration --- p.35
Chapter 4.2.1 --- Calibration of spectrometer --- p.36
Chapter 4.2.2 --- Calibration of movement stages --- p.38
Chapter 4.3 --- Data presentation for dispersion relation --- p.40
Chapter 4.4 --- Summary --- p.41
Chapter Chapter 5 --- Understanding of Fundamental Properties of SPPs --- p.43
Chapter 5.1 --- Excitation of SPPs on 2D hole arrays --- p.44
Chapter 5.2 --- Properties of non degenerate modes and theoretical explanation --- p.53
Chapter 5.2.1 --- Dependence of lifetime on hole geometry and theoretical explanation --- p.55
Chapter 5.2.2 --- Dependence of generation efficiency on hole geometry and theoretical explanation --- p.63
Chapter 5.3 --- Properties of degenerate modes and theoretical explanation --- p.70
Chapter 5.3.1 --- Dependence of properties of degeneration modes on hole geometry by FDTD --- p.72
Chapter 5.3.1.1 --- (0, ±l)[subscript s,a] modes --- p.72
Chapter 5.3.l.2 --- (-1, ±l)[subscript s,a] modes --- p.76
Chapter 5.3.2 --- Understanding of excitation of degenerate modes by using interference method --- p.79
Chapter 5.3.3 --- Understanding of coupling between degenerate modes by using coupled mode theory --- p.85
Chapter 5.4 --- Evolution of dispersion relation as hole depth increases --- p.90
Chapter 5.5 --- Summary --- p.95
Chapter Chapter 6 --- Surface Plasmon Resonance Based Label Free Biosensor --- p.98
Chapter 6.1 --- Basics of surface plasmon resonance (SPR) based biosensor --- p.98
Chapter 6.2 --- State-of-the-art SPR biosensor --- p.101
Chapter 6.3 --- SPR biosensor by using 2D metallic hole arrays --- p.102
Chapter 6.4 --- Summary --- p.111
Chapter Chapter 7 --- Conclusions --- p.112
References --- p.116
Publications --- p.126