Much of the interest in bent-core compounds in the last few years has centred aroundtheir potential to form nematic liquid crystal phases, which may be both biaxial andpolar. These properties offer possibilities for nematic ferroelectric switching andnonlinear optics applications. In this work, two optical properties, the refractive indices and the second ordernonlinear optical response, were investigated in the high temperature (> 170 °C)nematic phase of a series of bent-core oxadiazole compounds, of varying chain typeand length. An experimental technique, based on the acquisition and analysis of reflectionspectra from liquid crystal cells, and capable of operating at the high temperaturesrequired, was used for the measurement of refractive indices. The extraordinaryrefractive index was found to range from 1.70 to 1.78 over the nematic phase of thebent-core compounds. The ordinary refractive index varied from 1.58 to 1.62. Bothranges of values are higher than is typically observed for rod-like liquid crystals. Thebirefringence took values from ~ 0.10, in the high temperature nematic phase, to~ 0.18, close to the underlying smectic phase. A new experiment was designed, constructed and tested for the second harmonic(SH) measurements. The dependences of the SH on temperature and on scatteringangle are well explained by the theory of SH generation by the flexoelectricpolarisation induced by thermal fluctuations of the director in the nematic phase. Themaximum conversion efficiency was measured to be very low, ~ 1/10000 of apercent. No evidence for the formation of macroscopic biaxial nematic phases was found byeither the refractive indices or SH experiments. However, for the compounds havinglong nematic phases of > 50 °C, different regimes of behaviour in the uniaxialnematic phase were revealed by the SH experiments. This atypical behaviour isconsistent with other reports on these compounds. This study cannot confirm the existence of nanoscale cybotactic clusters in thenematic phases of the bent-core compounds examined but neither is it inconsistentwith them.

The evolution of electronics has become the staple thrust of modern scientific innovation: a need for advancing materials engineered for our equally rapidly advancing needs and computing requirements has fueled recent wealth of new materials. Here, I use the ideals of exotic materials design to answer this need, specifically for 2D materials. Two-dimensional (2D) van der Waals materials with in-plane anisotropy are of great interest for directional transport of charge and energy. I perform solid state synthesis to produce several such materials: an intrinsic antiferromagnet, superatomic semiconductors, and a polytype system with a component that displays the possibilities of Weyl nodes.The former, chromium sulfur bromide (CrSBr), is first synthesized, then fully studied structurally, compositionally, electronically, and magnetically. Second harmonic generation (SHG), more advanced than older techniques such as magneto-optical Kerr spectroscopy or Raman spectroscopy, allows us to fully understand the magnetic symmetry in this system as an interlayer antiferromagnetic and intralayer ferromagnetic in-plane anisotropic material. I also introduce published work in which we integrate CrSBr into different devices to show the utility of this fundamental research into a more practical application setting. It is used to stimulate more magnetic response from graphene — promising ultra-thin magnetic memory or sensory devices in future projects. Applying strain and external magnetic fields provides another tuning knob through which to access different functional modalities. In the latter third of this dissertation, we report a layered van der Waals semiconductor with in-plane anisotropy built upon the superatomic units of Mo₆S₃Br₆ (MSB), a robust construction with a direct gap of 1.64 eV. Next, MSB and Re₆Se₈Cl₂, another analogous superatomic vdW material, are potential candidates for optoelectronic applications; we qualify this by studying their Auger dynamics as a measure of quantum efficiency. Finally, layered van der Waals (vdW) materials belonging to the MM’Te₄ structure class have recently received intense attention due to their ability to host exotic electronic transport phenomena, such as in-plane transport anisotropy, Weyl nodes, and superconductivity. In summary, we have discovered two ternary exfoliatable vdW TMD polytypes with the composition TaFeTe₄, one of which (ꞵ) shows the prerequisite symmetry elements to be a type-II Weyl semimetal. This dissertation is a treatise to solid state synthesis, exploration into the more exotic spectrum of 2D materials, and robust and eclectic methods used to paint a full picture of different magnetic and electronic systems within.

<p>The symmetry requirements of both second harmonic generation (SHG) and triboluminescence (TL) provide outstanding selectivity to noncentrosymmetric crystals, leading to high signal to noise measurements of crystal growth and nucleation of active pharmaceutical ingredients (API) within amorphous solid dispersions (ASD) during accelerated stability testing. ASD formulations are becoming increasingly popular in the pharmaceutical industry due to their ability to address challenges associated with APIs that suffer from poor dissolution kinetics and low bioavailability as a result of low aqueous solubility. ASDs kinetically trap APIs into an amorphous state by dispersing the API molecules within a polymer matrix. The amorphous state of the API leads to an increase in apparent solubility, faster dissolution kinetics, and an increase in bioavailability. Both SHG and TL are used to quantitatively and qualitatively detect the crystal growth and nucleation within ASD formulations at the parts per million (ppm) regime. TL is the emission of light upon mechanical disruption of a piezoelectrically active crystal. Instrumentation was developed to rapidly determine the qualitative presence of crystals within nominally amorphous pharmaceutical materials in both powders and slurries. SHG was coupled with a controlled environment for <i>in situ</i> stability testing (CEiST) to enable <i>in situ</i> accelerated stability testing of ASDs. Single particle tracking enabled by the CEiST measurements provided insights into crystal growth rate distributions present due to local differences within the material. Accelerated stability testing monitored by <i>in situ</i> measurements increased the signal to noise in recovered nucleation and crystal growth rates by suppressing the Poisson noise normally present within conventional accelerated stability tests. The disparities between crystal growth and nucleation kinetics on the surface versus within bulk material were also investigated by single particle tracking and <i>in situ </i>measurements. Crystals were found to grow faster in the bulk compared to single crystals growing on the surface while total crystallinity was found to be higher on the surface due to radial growth habits of crystals on the surface compared to columnar growth within the bulk. To increase the throughput of the <i>in situ </i>measurements, a temperature and relative humidity array (TRHA) was developed. The TRHA utilizes a temperature gradient and many individual liquid wells to enable the use of a multitude of different conditions at the same time which can reduce time required to inform formulations design of stability information. </p>

The scope of this PhD-thesis is the production and characterization of highly conductive ferroelectric domain walls in 5 mol% magnesium-doped lithium niobate single crystals. Therefore one domain wall is induced into a single domain sample by the means of a local poling procedure. The produced structure is contacted through evaporated macroscopic metal electrodes. Since domain walls typically exhibit low currents a high voltage treatment is applied to persistantly increase the conductance by several orders of magnitude. A deeper understanding of the mechansimn behind the transport characteristics is given via atomic force microscopy and Cherenkov second-harmonicgeneration-microscopy. The combinaiton of surface sensitive conduction measurements and three dimensional topology detection prove to be magnificent complementary methods. A clear correlation between inclination with respect to the z-axis and local conductivity is found. Through this correllation a simple and intuitive theory is derived inside the band model, which quantitativly explains the observed behaviour. Following some key process parameters like electrode material, poling procedure and doping of the lithiumniobate crystal are varied, while their influence on the high voltage treatment is investigated. Additionally the procedure is also applied to domain walls in lithium tantalate. Lastly domain walls are observed in real time under the influence of an electric field via Cherenkov second-harmonic-generation-microscopy. There is the possibillity of either two or three dimansional investigations while the latter bears a worse time resolution. It is shown that the speed of the domain wall movement holds a gradient along the z-axis, depending on the polarity of the electric field. / Die vorliegende Dissertation behandelt die Herstellung und Charakterisierung hochleitfähiger ferroelektrischer Domänenwände in 5 mol% magnesiumdotierten Lithiumniobat-Einkristallen. Dabei kommen eindomänige Probenstücke zum Einsatz in die durch lokale Umpolung eine einzelne Domänenwand induziert wird. Die makroskopische Kontaktierung der erzeugten Struktur erfolgt mit Hilfe von aufgedampften Metallelektroden. Da die Domänenwände üblicherweise nur sehr kleine Leitfähigkeiten zeigen wird durch eine Hochspannungsbehandlung selbige nachhaltig um mehrere Gröÿenordnungen erhöht. Einen tieferen Einblick in die Mechanismen der veränderten Transportcharakteristik gewähren die Rasterkraft- und Cherenkov-Second-Harmonic-Generation-Mikroskopie. Die Kombination aus oberflächensensitiver lokaler Leitfähigkeitsmessung und dreidimensionaler Topologieerfassung erweisen sich als ausgezeichnete komplementäre Methoden. Sie zeigen eine klare Korrelation zwischen Neigungswinkel der Wand im Verhältnis zur z-Achse und der gemessenen Leitfähigkeit. Über diesen Zusammenhang wird eine einfache, intuitive Theorie der Domänenwand im Bändermodell entwickelt, die das Verhalten quantitativ erklärt. Es folgt die Untersuchung verschiedener Prozessparameter wie Elektrodenmaterial, Polungsprozedur sowie Dotierung des Lithiumniobats und deren Einfluss auf die Hochspannungsbehandlung. Zudem wird diese auch an Lithiumtantalat-Kristallen getestet. Abschlieÿend wird eine Echtzeitmessung der Domänenwand unter angelegtem Feld mittels Cherenkov-Second-Harmonic-Generation-Mikroskopie durchgeführt. Diese ist dabei in zwei bzw. drei räumlichen Dimensionen möglich, wobei letztere eine geringere Zeitauflösung besitzt. Es wird deutlich, dass die Geschwindigkeit mit der sich die Domänenwand bewegt, einen Gradienten entlang der z-Achse aufweist. Dieser ist von der Polarität des elektrischen Feldes abhängig.

Plasmonic metasurfaces enable functionalities that extend beyond the possibilities of classical optical materials and as a result, have gained significant research interest over the years. This thesis aims towards introducing plasmonic metamaterials and metasurfaces, a two-dimensional subset of metamaterials. The thesis also provides insights into the nonlinear optical responses from subwavelength metallic nanostructures manifesting as extraordinary physical phenomena like the second harmonic generation (SHG). The hydrodynamic Drude model is a theory that characterizes electron conduction in a hydrodynamic way to predict optical responses of metals. The thesis discusses the various contributions to the second-order optical nonlinearities from the terms in the hydrodynamic model: Coulomb, convection, and the Lorentz magnetic force. The significance of these terms, specifically the Lorentz magnetic term, is validated in contrast with existing research. The details of the work carried out to achieve a significant contribution to SHG from the Lorentz magnetic term are provided. A dominant Lorentz magnetic force for SHG was achieved through engineering T-shaped aperture arrays milled into a thin gold film. The dimensions of these structures were tuned for fundamental wavelength resonance. The structures exhibit both magnetic and electric field enhancements at the plasmonic resonance. Furthermore, a revised theoretical model is developed to accurately predict both linear and nonlinear optical responses of metamaterials. The model is based on the hydrodynamic Drude model and nonlinear scattering theory. Results from the finite difference time domain simulations performed on the metasurface are presented. It is observed that the T-shaped structure provides 65% greater nonlinear generation from the Lorentz magnetic term than the sum of the other two hydrodynamic terms. The influence of incident beam polarization on SHG conversion efficiency was also investigated. It was discovered that even though the contributions of hydrodynamic (Coulomb and convection) terms are maximum at 0◦ and 90◦, the metasurface shows maximum SHG intensity at 45◦ which indicates a dominant Lorentz magnetic term. Experimental validation was performed using the fabricated metasurface and a good agreement between the experiment and theoretical calculations was observed. Another aspect of the magnetic Lorentz force contribution, Bethe’s aperture theory was evaluated for a circular aperture at off-normal incident light. It is shown that the Lorentz force dominates the SHG by an order of magnitude at angled incidence where the generation is maximized. The angular dependence was observed to match the magnetic and electric dipole interaction effects as predicted from Bethe’s theory. The revised theory developed in this thesis predicts the linear and nonlinear optical responses of metamaterials including their angular dependency. The analysis and numerical calculations for a circular aperture agree well with past experiments. To conclude, the thesis provides an outlook on future developments in the field of nonlinear plasmonic research with regards to the development of highly efficient nonlinear metasurfaces through optimization of the Lorentz contributions. An insight into the recent developments in nanofabrication capabilities, design methodologies, nano-characterization techniques, modern electromagnetic simulations is discussed as avenues for future research in nanophotonic and nanoplasmonic device design and development. / Graduate

L’optique non linéaire est un outil très puissant pour l’étude des propriétés photoniques de molécules, de matériaux et de nanostructures. La taille et la forme des nanoparticules de métaux nobles (NMNPs) influencent fortement leurs propriétés optiques non linéaires du second ordre. Dans cette thèse, nous proposons une étude systématique de l'influence de la surface de nanoparticules sur leurs valeurs de première hyperpolarisabilité bêta. Des nanoparticules en poudre d’argent (de diamètres 7 nm) ainsi que des solutions colloïdales sur NMNPs -avec différentes compositions, tailles et formes -ont été synthétisés : des nanosphères d'argent (de diamètres 10 nm), des nanosphères d’or (de diamètres 3,0; 11,6; 15,8; 17,4; 20,0 et 43,0 nm), des nanobâtonnets d’or (de rapports d'aspect 1,47; 1,63 et 2,30), des nanobâtonnets d’argent (de rapports d'aspect 5,0; 6,3; 7,5; 8,2 et 9,7), des nanofleurs de platine (de diamètres 7,0; 8,0; 10,0; 14,0; 20,0 et 31,0 nm) ainsi que des nanoprismes d'or (d’une longueur de côtés de 47,5 à 112,3 nm). La diffusion harmonique de la lumière (HLS) à 1064 nm est utilisée pour étudier la génération du second harmonique des NMNPs colloïdaux, et d'en déduire leurs valeurs de première hyperpolarisabilité bêta. Pour les nanosphères et les nanorods étudiés dans ce travail, nous démontrons que leurs valeurs de bêta présentent une forte dépendance avec leur surface, qui est le paramètre dominant dans l'évolution des valeurs de bêta. Par ailleurs, la rugosité de la surface des particules ainsi que la forme des irrégularités des nanofleurs sont responsables de valeurs exceptionnellement élevées de bêta. En outre, nous démontrons expérimentalement, pour la première fois dans la littérature, que les valeurs de bêta des nanoprismes présentent non seulement une dépendance linéaire par rapport à la surface, mais sont également sensibles aux courbures des sommets du triangle. / Nonlinear optics is well known to be a highly powerful tool to investigate the photonic properties of molecules, materials and nanostructures. Size and shape of noble metal nanoparticles (NMNPs) strongly influence their second-order nonlinear optical properties. In this PhD thesis, we propose a systematic investigation of the influence of the nanoparticle surface area on their first hyperpolarizability beta values. Powdery-silver nanoparticles (diameters 7 nm) and colloidal solutions on NMNPs with different composition, sizes and shapes have been synthesized, i.e. silver nanospheres (diameters 10 nm), gold nanospheres (diameters 3.0; 11.6; 15.8; 17.4; 20.0 and 43 nm), gold nanorods (aspect ratios 1.47; 1.63 and 2.30), silver nanorods (aspect ratios 5.0; 6.3; 7.5; 8.2 and 9.7), platinum nanoflowers (diameters 7.0; 8.0; 10.0; 14.0; 20.0 and 31.0 nm) and gold nanoprisms (edge length tuned from 47.5 to 112.3 nm). Harmonic light scattering (HLS) at 1064 nm is used to investigate the second harmonic generation from colloidal NMNPs, and to infer their first hyperpolarizability tensor beta. For the nanospheres and nanorods investigated in this work, we demonstrate that their beta values display a strong dependence with their surface area, which is the dominant parameter in the evolution of beta values. Otherwise, particle surface corrugation and shape irregularities of nanoflowers are responsible for exceptionally high beta values. Moreover, we report for the first time in the literature that the beta values of nanoprisms display not only a linear dependence with respect to the surface area, but are also sensitive to the sharpness of the triangle vertices.

<p>Laser-based displays have been under active development over the past 50 years. Visible lasers are considered as the “ultimate” light sources for display applications due to their high brightness, high directionality and high color saturation. Unlike commercially available red and blue laser diodes, semiconductor laser diodes that can directly emit green light with sufficient power and efficiency required in laser display are still not ready yet. Significant effort has been paid around the world to overcome this “green bottleneck”.</p> <p>The aim of this thesis is to investigate a practical solution to build a compact green laser to satisfy the cost/performance requirement for laser display applications. Frequency doubling based on MgO doped periodically poled lithium niobate (MgO:PPLN) is the main research direction of this thesis work.</p> <p>The thesis focuses on several engineering issues, mainly related to practical applications. Two different approaches have been explored: single-pass frequency doubling and intra-cavity frequency doubling. In the single-pass configuration, an all-fiber Q-switched fiber laser was used as the fundamental laser source because the high peak pump power can increase the conversion efficiency. 3.1%/W/cm nonlinear conversion efficiency was achieved which show good agreements with the theoretical simulations. The single-pass frequency doubling of a novel annealing proton exchanged (APE) MgO:PPLN ridge waveguide was also investigated. Over 120 mW green laser with a 53.2% conversion efficiency was achieved. The results have shown remarkable improvements comparing with the reported waveguide devices.</p> <p>On the other hand, in the intra-cavity frequency doubling, Nd:YVO₄/MgO:PPLN microchips for low power (300 mW CW green power and 530 mW modulated green power) applications have been demonstrated experimentally and investigated theoretically. It has been shown that although the plane-parallel cavity structure with discrete components can provide 2.9 W green laser with 29.6% conversion efficiency, it is complex for mass production. One of the important research achievements of this thesis is to study and optimization of a novel monolithically integrated Nd:YVO₄/MgO:PPLN module (namely mGreen module) which combines the advantages of the microchip structure and the discrete plane-parallel cavity structure. 1.28 Watt output green laser has been achieved through a compact configuration based on the optimized mGreen module. Power scaling based on this monolithic green laser module by employing an array concept has also been investigated. The dependence of output power on pump beam gap has been studied both theoretically and experimentally.</p> / Doctor of Philosophy (PhD)

In this dissertation, the laser spectroscopic methods, second harmonic generation (SHG) and ultrafast transient absorption, have been employed to study the reactions and dynamics in two different types of materials, namely, silver nanoparticles and micro-sized ultrathin crystalline oligoacenes. These two materials, although both are in small dimensions, represent two distinct types of systems with divergent characteristics: 1) systems in which interactions at the surface/interface are dominant, and 2) systems in which bulk interactions are dominant. Silver nanoparticles are an important member of the class of noble metal nanoparticles, and possess unique optical and chemical properties due to their ultrafine size and high surface-to-volume ratio. Strong SHG signal has been observed from silver nanoparticles dispersed in aqueous colloidal solution, in which the SHG signal is enhanced due to a resonance with the localized surface plasmon of silver nanoparticles. Further experiments proved that the SHG signal predominantly originates from the particle surface, in full agreement with the intrinsically interface-sensitive properties of SHG. With the surface origin of the signal now well established, SHG can be used to probe the adsorption and reactions of thiol molecules at the nanoparticle surface in situ and in real time. It is experimentally demonstrated that the free energy change, activation energy, as well as adsorption density of the reactions of a variety of neutral and anionic thiols at the particle surface can be measured by means of SHG. The reaction mechanisms at the molecular level have been deduced, and the neutral vs anionic thiols are found to exhibit qualitatively different reaction mechanisms that reflect the effect of their molecular interactions with the particle surface. Oligoacenes, such as pentacene and hexacene, constitute a family of organic semiconductors that exhibit remarkable optoelectronic properties. In contrast to the nanoparticles in which surface interactions are dominant, as the sizes of materials become larger, the bulk characteristics become more deterministic. Therefore, polarized linear absorption and transient absorption spectroscopies have been applied to study the excitonic properties of crystalline pentacene and the mechanism of singlet fission in crystalline hexacene, respectively. The polarized absorption spectra of crystalline pentacene have been obtained by measuring transmitted light normal to the ab herringbone plane of micro-sized ultrathin single crystals. The significant deviations between the spectral line shapes polarized along the b-axis and orthogonal to the b-axis provide detailed information on the anisotropic mixing nature of the Frenkel/charge-transfer excitons responsible for the pronounced Davydov splitting between the lowest-energy singlet states. Additionally, both singlet and triplet Davydov splittings were also observed from the linear and transient absorption experiments in micrometer-sized ultrathin hexacene single crystals. A two-step process of anisotropic singlet fission was uncovered from the kinetic data, in which singlet fission at different rates were deduced along the a- and b-axes. Both the spectral and kinetic features indicate that singlet fission in crystalline hexacene is an anisotropic and charge-transfer mediated many-molecule process. / Chemistry

Ionically self-assembled monolayer (ISAM) films are typically an assemblage of oppositely charged polymers built layer by layer through Coulombic attraction utilizing an environmentally friendly process to form ordered structures that are uniform, molecularly smooth and physically robust. ISAM films have been shown to be capable of the noncentrosymmetric order requisite for a second-order nonlinear optical response with excellent temporal and thermal stability. However, such films fabricated with a nonlinear optical (NLO) polyanion result in significant cancellation of the chromophore orientations. This cancellation occurs by two mechanisms: competitive orientation due to the ionic bonding of the polymer chromophore with the subsequent polycation layer, and random orientation of the chromophores within the bulk of each polyanion layer. A reduction in film thickness accompanied by an increase in net polar ordering is one possible avenue to obtain the second-order susceptibility chi(2) necessary for practical application in electro-optic devices. In this thesis, we discuss the structural characteristics of ISAM films and explore a novel approach to obtain the desired characteristics for nonlinear optical response. This approach involves a hybrid covalent / ionic self-assembly technique which affords improved net dipole alignment and concentration of monomer chromophores in the film. This technique yields a substantial increase in chi(2) due to the preferential chromophore orientation being locked in place by a covalent bond to the preceding polycation layer. The films fabricated in this manner yield a chi(2) that substantially exceeds that of any known polymer-polymer ISAM film. This covalent-hybrid ionically self-assembled multilayer (CHISAM) technique is demonstrated to result in films suitable for electro-optic devices, with measured electro-optic coefficient (14 pm/V) comparable to that of the inorganic crystal lithium niobate (30 pm/V). Thermal and temporal stability are important properties of electro-optic device implementation, and are demonstrated for CHISAM films. CHISAM films have remained stable at room temperature for more than 420 days, and suffered no loss of chi(2) when held at 80 C for 36 hours, followed by 150 C for 24 hours. Studies are also presented that demonstrate the ability to produce ISAM chi(2) films that are nearly one micron thick, and exhibit no evidence of a thickness limitation to the polar order. Analytical considerations for second-order NLO characterization of thick films are addressed in detail. The effect of absorption of the second harmonic wavelength and resonant enhancement of chi(2) are investigated, and it is demonstrated that accurate determination of chi(2) may be made for thick films and for films that absorb the second harmonic. The temporal and thermal stability of a variety of ISAM and CHISAM NLO films are examined in detail. In some cases, a decrease in the NLO response is observed at elevated temperature that is completely restored upon cooling. Studies are presented that suggest this effect is a result of thermally induced trans-to-cis isomerization of azo linkages in the NLO chromophores. / Ph. D.

Owing to its centrosymmetric structure, the critical optical component of a silica fiber cannot to possess a second-order nonlinear optical susceptibility, Χ(²), preventing a silica fiber from many potential applications. Here, we theoretically and experimentally demonstrate a new technique to generate large and thermodynamically stable second-order nonlinearity into silica optical tapered fibers without breaking the centrosymmetry of the silica glass. The nonlinearity is introduced by surface layers with high polar-ordering fabricated by a novel hybrid covalent/ionic self-assembly multilayer technique. Despite the overall rotational symmetry of the nonlinear fiber, we observe significant second harmonic generation with ~ 400–500 fold enhancement of the SHG power compared to the traditional tapers. Phase matching for a SHG process in second-order nonlinear tapered fibers is also realized by the compensation of waveguide modal dispersion with material chromatic dispersion, which occurs only for submicron tapers where the modal dispersion is large. In addition, quasi-phase-matching for a nonlinear taper can be accomplished by introducing a periodic pattern into the nonlinear film coating. We use UV laser ablation for the controlled removal of particular nonlinear film segments on a taper surface in order to produce a Χ(²) grating structure. A resulting SHG enhancement from quasi-phase-matching is observed over a broadband spectrum of the pump light mainly due to the non-uniform shape of a taper waveguide. The laser ablation is a clean and fast technique able to produce well-define patterns of polymer films on either flat or curved substrate geometry. With surface layers containing reactive functional groups e.g. primary amines, we demonstrate that the resulting patterned film obtained from the laser ablation can be used as a template for further self-assembly of nanoparticles with high selectivity. A pattern feature size down to ~ 2μm or smaller can be fabricated using this approach. We also discuss preliminary results on a novel technique to further improve spatial accuracy for selective self-assembly of nanoparticles at an unprecedented level. Different types of nanoparticles are joined in order to form well-defined, molecular-like superstructures with nanoscale accuracy and precision. The technique is based on a selective surface functionalization of photosensitive molecules coated on metallic nanoparticles utilizing enhanced two-photon photocleavage at the plasmonically-active sites (hot spots) of the nanoparticles in resonance with an applied electromagnetic wave. As a result, the surface functional groups at the nanoparticle hot spots are different from the the other areas, allowing other kinds of nanoparticles to self-assemble at the hot spots with high degree of selectivity. / Ph. D.