My Ph.D. thesis is presented in two parts. In the first part, I describe the preparation of organic-inorganic hybrid micelles formed from poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) block copolymers and CdSe quantum dots (QDs). Several distinct morphologies were observed including, spheres, finite-sized wormlike networks and clusters of hollow vesicles. A series of experiments were carried out to explore whether these hybrid colloids were thermodynamically stable or formed under kinetic control. Upon addition of 2-propanol (2-PrOH) to a chloroform solution containing a mixture of PS404-b-P4VP76 plus CdSe QDs (2-PrOH is a good solvent for P4VP block and a precipitant for PS block and QDs), uniform spherical micelles formed almost instantly, with a PS core and a thin P4VP corona to which the QDs were attached. Vigorous stirring of this solution for two days led to the formation of three-dimensional wormlike networks consisted of Y-junctions and cylindrical struts, terminated by bulbous spherical end-caps. Even more profound structural changes occurred when the solution was subjected to prolonged magnetic stirring (e.g. 1 month). ii In contrast, manipulating the chemical composition of the initial block copolymer could trigger a spontaneous structural transition from sphere to network of wormlike micelles over 2 h without the need of stirring. The second part of the thesis begins by describing a modular approach for preparing polyferrocenyldimethylsilane (PFS) block copolymers via a Cu-catalyzed alkyne/azide coupling reaction to covalently combine two homopolymers synthesized separately. This strategy opens the door to a broad library of novel functional PFS block copolymers, for example, poly(ferrocenyldimethylsilane-b-N-isopropyl acrylamide) (PFS-b-PNIPAM). In an attempt to expand our understanding of PFS block copolymer self-assembly in polar solvents, I investigated the self-assembly of a new polymer (PFS26-b-PNIPAM105) in alcohol solvents. When the block polymer was dissolved in methanol, ethanol and 2-propanol, it formed long fiber-like micelles with uniform width. I also showed that micelles of this polymer underwent seeded growth in methanol, leading to cylindrical micelles that were nearly mono- dispersed in length.

My Ph.D. thesis is presented in two parts. In the first part, I describe the preparation of organic-inorganic hybrid micelles formed from poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) block copolymers and CdSe quantum dots (QDs). Several distinct morphologies were observed including, spheres, finite-sized wormlike networks and clusters of hollow vesicles. A series of experiments were carried out to explore whether these hybrid colloids were thermodynamically stable or formed under kinetic control. Upon addition of 2-propanol (2-PrOH) to a chloroform solution containing a mixture of PS404-b-P4VP76 plus CdSe QDs (2-PrOH is a good solvent for P4VP block and a precipitant for PS block and QDs), uniform spherical micelles formed almost instantly, with a PS core and a thin P4VP corona to which the QDs were attached. Vigorous stirring of this solution for two days led to the formation of three-dimensional wormlike networks consisted of Y-junctions and cylindrical struts, terminated by bulbous spherical end-caps. Even more profound structural changes occurred when the solution was subjected to prolonged magnetic stirring (e.g. 1 month). ii In contrast, manipulating the chemical composition of the initial block copolymer could trigger a spontaneous structural transition from sphere to network of wormlike micelles over 2 h without the need of stirring. The second part of the thesis begins by describing a modular approach for preparing polyferrocenyldimethylsilane (PFS) block copolymers via a Cu-catalyzed alkyne/azide coupling reaction to covalently combine two homopolymers synthesized separately. This strategy opens the door to a broad library of novel functional PFS block copolymers, for example, poly(ferrocenyldimethylsilane-b-N-isopropyl acrylamide) (PFS-b-PNIPAM). In an attempt to expand our understanding of PFS block copolymer self-assembly in polar solvents, I investigated the self-assembly of a new polymer (PFS26-b-PNIPAM105) in alcohol solvents. When the block polymer was dissolved in methanol, ethanol and 2-propanol, it formed long fiber-like micelles with uniform width. I also showed that micelles of this polymer underwent seeded growth in methanol, leading to cylindrical micelles that were nearly mono- dispersed in length.

Environmental and economic factors demand radical advances in solar cell technologies. Organic and polymer photovoltaics emerged in the 1990's that have led to low cost per unit area, enabled in significant part by the convenient manufacturing of roll-to-roll-processible solution-cast semiconductors. Colloidal quantum dot solar cells dramatically increase the potential for solar conversion efficiency relative to organics by enabling optimal matching of a photovoltaic device's bandgap to the sun's spectrum. Infrared-absorbing colloidal quantum dot solar cells were first reported in 2005. At the outset of this study in 2007, they had been advanced to the point of achieving 1.8% solar power conversion efficiency. These devices degraded completely within a few hours’ air exposure. The origin of the extremely poor device stability was unknown and unstudied. The efficiency of these devices was speculated to be limited by poor carrier transport and passivation within the quantum dot solid, and by the limitations of the Schottky device architecture. This study sought to tackle three principal challenges facing colloidal quantum dot photovoltaics: stability; understanding; and performance. In the first part of this work, we report the first air-stable infrared colloidal quantum dot photovoltaics. Our devices have a solar power conversion efficiency of 2.1%. These devices, unencapsulated and operating in an air atmosphere, retain 90% of their original performance following 3 days’ continuous solar harvesting. The remarkable improvement in device stability originated from two new insights. First, we showed that inserting a thin LiF layer between PbS film and Al electrode blocks detrimental interfacial reactions. Second, we proposed and validated a model that explains why quantum dots having cation-rich surfaces afford dramatically improved air stability within the quantum dot solid. The success of the cation-enrichment strategy led us to a new concept: what if - rather than rely on organic ligands, as all prior quantum dot photovoltaics work had done - one could instead terminate the surface of quantum dots exclusively using inorganic materials? We termed our new materials strategy ionic passivation. The goal of the approach was to bring our nanoparticles into the closest possible contact while still maintaining quantum confinement; and at the same time achieving a maximum of passivation of the nanoparticles' surfaces. We showcase our ionic passivation strategy by building a photovoltaic device that achieves 5.8% solar power conversion efficiency. This is the highest-ever solar power conversion efficiency reported in a colloidal quantum dot device. More generally, our ionic passivation strategy breaks the past tradeoff between transport and passivation in quantum dot solids. The advance is relevant to electroluminescent and photodetection devices as well as to the record-performing photovoltaic devices reported herein.

Solution processed solar cells offer the promise of a low cost solution to global energy concerns. Colloidal quantum dots are one material that can be easily synthesized in and deposited from solution. These nanoparticles also offer the unique ability to select the desired optical and electrical characteristics, all within the same materials system, through small variations in their physical dimensions. These materials, unfortunately, are not without their limitations. To date, films made from colloidal quantum dots exhibit limited mobilities and short minority diffusion lengths. These limitations imply that simple device structures may not be sufficient to make an efficient solar cell. Here we show that through clever manipulation of the geometric and energetic structures, we can utilize the size-tunability of CQDs while masking their poor electrical characteristics. We further outline the physical mechanisms present within these architectures, namely the utilization of a distributed built-in electric field to extract current through drift rather than diffusion. These architectures have consequently exceeded the performance of legacy architectures such as the Schottky cell. Finally, we discuss some of the limiting modes within these architectures and within CQD films in general including the impact of surface traps and polydispersity in CQD populations. Through the development of these novel architectures, the power conversion efficiency of CQD solar cells has increased from ~3.5% to 7.4%; the highest efficiencies yet reported for colloidal quantum dot solar cells.

Studies various nanostructured materials have gained considerable interest within the past several decades. This novel class of materials has opened up a new realm of possibilities, both for the fundamental comprehension of matter, but also for innovative applications. The size-dependent effect observed for these systems often lies in their interaction with the surrounding environment and understanding such interactions is the pivotal point for the investigations undertaken in this thesis. Three families of nanoparticles are analyzed: semiconductor quantum dots, metallic silver nanoparticles and rare-earth oxide nanomaterials. The radical scavenging ability of cerium oxide nanoparticles (CeO2) is quite controversial since they have been labeled as both oxidizing and antioxidant species for biological systems. Here, both aqueous and organic stabilized nanoparticles are examined in straightforward systems containing only one reactive oxygen species to ensure a controlled release. The apparent absence of their direct radical scavenging ability is demonstrated despite the ease at which CeO2 nanoparticles generate stable surface Ce3+ clusters, which is used to explain the redox activity of these nanomaterials. On the contrary, CeO2 nanoparticles are shown to have an indirect scavenging effect in Fenton reactions by annihilating the reactivity of Fe2+ salts. Cadmium selenide quantum dots (CdSe QD) constitute another highly appealing family of nanocolloids in part due to their tunable, size-dependent luminescence across the visible spectrum. The effect of elemental sulfur treatment is investigated to overcome one of the main drawbacks of CdSe QD: low fluorescence quantum yield. Herein, we report a constant and reproducible quantum yield of 15%. The effect of sulfur surface treatment is also assessed following the growth of a silica shell, as well as the response towards a solution quencher (4-amino-TEMPO). The sulfur treated QD is also tested for interaction with pyronin Y, a xanthene dye that offers potential energy and electron transfer applications with the QD. Interaction with the dye molecule is compared to results obtained with untreated quantum dots, as well as CdSe/ZnS core shell examples. In another chapter of this thesis, the catalytic potential of silver nanoparticles is addressed for the grafting of polyhydrosiloxane polymer chains with various alkoxy groups. A simple one-pot synthesis is presented with silver salts and the polymer. the latter serves as a mild reducing agent and a stabilizing ligand, once silver nanoparticles are formed in-situ. We evaluate the conversion of silane into silyl ethers groups with the addition of several alcohols, whether primary, secondary or tertiary, and report the yields of grafting under the mildest conditions: room temperature, under air and atmospheric pressure.

This thesis focuses on pioneering a scalable route to fabricate quantum information devices based upon single InAs/InP quantum dots emitting in the telecommunications wavelength band around 1550 nm. Using metallic gates in combination with nanotemplate, site-selective epitaxy techniques, arrays of single quantum dots are produced and electrostatically tuned with a high degree of control over the electrical and optical properties of each individual quantum dot. Using metallic gates to apply local electric fields, the number of electrons within each quantum dot can be tuned and the nature of the optical recombination process controlled. Four electrostatic gates mounted along the sides of a square-based, pyramidal nanotemplate in combination with a flat metallic gate on the back of the InP substrate allow the application of electric fields in any direction across a single quantum dot. Using lateral fields provided by the metallic gates on the sidewalls of the pyramid and a vertical electric field able to control the charge state of the quantum dot, the exchange splitting of the exciton, trion and biexciton are measured as a function of gate voltage. A quadrupole electric field configuration is predicted to symmetrize the product of electron and hole wavefunctions within the dot, producing two degenerate exciton states from the two possible optical decay pathways of the biexciton. Building upon these capabilities, the anisotropic exchange splitting between the exciton states within the biexciton cascade is shown to be reversibly tuned through zero for the first time. We show direct control over the electron and hole wavefunction symmetry, thus enabling the entanglement of emitted photon pairs in asymmetric quantum dots. Optical spectroscopy of single InAs/InP quantum dots atop pyramidal nanotemplates in magnetic fields up to 28T is used to examine the dispersion of the s, p and d shell states. The g-factor and diamagnetic shift of the exciton and charged exciton states from over thirty single quantum dots are calculated from the spectra. The g-factor shows a generally linear dependence on dot emission energy, in agreement with previous work on this subject. A positive linear correlation between diamagnetic coefficient and g-factor is observed.

De récentes avancées technologiques laissent entrevoir le potentiel des spins électroniques uniques comme supports pour le stockage et la manipulation de l'information. En raison de leur nature quantique, les spins électroniques contrôlé à l’échelle de l’électron unique peuvent non seulement être utilisés pour stocker l'information classique, mais pourraient également être mis en œuvre pour réaliser des qubits dans un ordinateur quantique. Dans un tel dispositif, les superpositions de différents états de spin peuvent être utilisées pour calculer plus efficacement que les ordinateurs classiques.Une mise en œuvre prometteuse d'un tel système est un électron piégé dans une boite quantique latérale. Ce dispositif nanométrique défini dans des structures semiconductrices permet d'isoler et de manipuler le spin d’un électron de façon cohérente avec des potentiels électrostatiques. Dans cette thèse, nous manipulons les électrons dans des boites quantiques dans un régime dit « isolé». La manipulation de charges électroniques individuelles en plusieurs boites quantiques connectées entre elles apparaît alors être simplifiée. Cette manipulation de spin se fait grâce à l’échange cohérent d’un quantum de spin entre deux électrons piégés. Le contrôle du couplage tunnel entre ces deux boites quantiques rend cet échange contrôlé. De cette façon, la manipulation de spin peut se faire à un "sweet spot", un point insensible au bruit de charge, permettant ainsi d'obtenir des oscillations de spin de haute qualité.Le contrôle précis de la charge dans le régime isolé est ensuite utilisé pour contrôler le déplacement d’un électron dans un système circulaire de trois boites quantiques qui sont fortement couplées par effet tunnel. Ainsi la cohérence d'une superposition de deux spins électroniques déplacée le long d’une boucle fermée a été étudiée. Nos mesures montrent le transport cohérent de spins électroniques uniques sur des distances allant jusqu'à 5 μm. Pendant le transfert, le temps de cohérence se révèle être considérablement augmenté. Nous avons identifié le mécanisme sous-jacent à cette amélioration comme provenant d’un rétrécissement, lors du mouvement, des gradients de champ nucléaires générées par l'environnement cristallin. Les sources de décohérence sont discutées et permettent d’obtenir de nouvelles connaissances sur la dynamique interne du processus de transfert entre des boites quantiques couplées. Nos résultats sur le transport cohérent d'électrons peuvent être utilisés pour évaluer les possibilités d’intégration à grande échelle de qubits de spin dans des réseaux de boites quantiques à deux dimensions. / Recent technological advances hint at the future possibility to use single electron spins as carriers and storage of information. Due to their quantum nature, individually controlled electron spins can not only be used to store classical information, but could also find implementation as quantum bits in a quantum computer. In this envisioned device, the superposition of different spin states could be used to perform novel calculation procedures more efficiently than their classical counterparts.A promising implementation of a controllable single electron spin system is an electron trapped in a lateral quantum dot. This nanoscale solid state device allows to isolate and coherently manipulate the spin of individual electrons with electrostatic potentials. In this thesis we study electrons in quantum dot structures using a manipulation technique which we call the "isolated regime". In this regime the manipulation of individual electron charges in several connected quantum dots is shown to be simplified. This allows to implement a novel spin manipulation scheme to induce coherent exchange of a quantum of spin between two electrons via a variation of the tunnel-coupling between adjacent quantum dots. This manipulation scheme is observed to lead to a reduced sensibility to charge noise at a "sweet spot" and thereby allows to obtain high quality spin oscillations.The improved charge control in the isolated regime is then used to achieve circular coupling in a triple quantum dot device with high tunnel-rates. This allows to directly probe the coherence of a superposition of two electron spins which are displaced on a closed loop in the three quantum dots. Our measurements demonstrate coherent electron transport over distances of up to 5 μm. During the transfer the coherence time is found to be significantly increased. We identify the underlying mechanism for the enhancement with a motional narrowing of the nuclear field gradients originating from the crystal environment. The limiting decoherence source is found to be single electron spin-flips induced by a real space motion of the electrons. Our results on the coherent transport of electrons can be used to asses the scaling possibilities of spin qubit implementations on two-dimensional lattices.

abstract: As the 3rd generation solar cell, quantum dot solar cells are expected to outperform the first 2 generations with higher efficiency and lower manufacture cost. Currently the main problems for QD cells are the low conversion efficiency and stability. This work is trying to improve the reliability as well as the device performance by inserting an interlayer between the metal cathode and the active layer. Titanium oxide and a novel nitrogen doped titanium oxide were compared and TiOxNy capped device shown a superior performance and stability to TiOx capped one. A unique light anneal effect on the interfacial layer was discovered first time and proved to be the trigger of the enhancement of both device reliability and efficiency. The efficiency was improved by 300% and the device can retain 73.1% of the efficiency with TiOxNy when normal device completely failed after kept for long time. Photoluminescence indicted an increased charge disassociation rate at TiOxNy interface. External quantum efficiency measurement also inferred a significant performance enhancement in TiOxNy capped device, which resulted in a higher photocurrent. X-ray photoelectron spectrometry was performed to explain the impact of light doping on optical band gap. Atomic force microscopy illustrated the effect of light anneal on quantum dot polymer surface. The particle size is increased and the surface composition is changed after irradiation. The mechanism for performance improvement via a TiOx based interlayer was discussed based on a trap filling model. Then Tunneling AFM was performed to further confirm the reliability of interlayer capped organic photovoltaic devices. As a powerful tool based on SPM technique, tunneling AFM was able to explain the reason for low efficiency in non-capped inverted organic photovoltaic devices. The local injection properties as well as the correspondent topography were compared in organic solar cells with or without TiOx interlayer. The current-voltage characteristics were also tested at a single interested point. A severe short-circuit was discovered in non capped devices and a slight reverse bias leakage current was also revealed in TiOx capped device though tunneling AFM results. The failure reason for low stability in normal devices was also discussed comparing to capped devices. / Dissertation/Thesis / M.S. Materials Science and Engineering 2011

Here we present direct investigation of the lasing behaviour by performing gain spectroscopy of solution-based CQDs enabled via in-situ tuning of the feedback wavelength of an open-access hemispherical microcavity. The investigation is performed on two different types of CQDs, namely spherical CdSe/CdS core-shell CQDs and nanopletelets (NPs). The lasing threshold and the differential gain/slope efficiency of the fundamental cavity mode are measured as a function of their spectral position over a spectral range of ∼ 32 nm and of ∼ 42 nm for the spherical CQDs and NPs, respectively. The results of the gain spectroscopy are described using theoretical models, providing insights into the mechanism governing the observed lasing behaviour. Furthermore, the open-access cavity architecture provides a very convenient way of producing in-situ tunable lasing, and single-mode lasing of the fundamental cavity mode over a spectral range of ∼ 25 nm and ∼ 37 nm is demonstrated using spherical CQDs and NPs, respectively. In addition, the stability of laser emission is investigated, with the lasing intensity of the fundamental cavity mode remaining constant over a time period of almost 6 mins. It is hoped that the results will provide a detailed understanding of the lasing behaviour of CQDs. This information can be fed back into the design of CQDs in which the lasing threshold can be reduced to the point where useful devices can be constructed, and in the design of resonant optical feedback structures for which the appropriate wavelength must be carefully selected.

This dissertation contains six chapters detailing recent advances that have been made in the synthesis and characterization of metal-semiconductor hybrid nanocrystals (HNCs), and the applications of these materials. Primarily focused on the synthesis of well-defined II-VI semiconductor nanorod (NR) and tetrapod (TP) based constructs of interest for photocatalytic and solar energy applications, the research described herein discusses progress towards the realization of key design rules for the synthesis of functional semiconductor nanocrystals (NCs). As such, a blend of novel synthesis, advanced characterization, and direct application of heterostructured nanoparticles are presented. Additionally, for chapters two through six, a corresponding appendix is included containing supporting data pertinent to the experiments described in the chapter. The first chapter is a review summarizing the design, synthesis, properties, and applications of multicomponent nanomaterials composed of disparate semiconductor and metal domains. By coupling two compositionally distinct materials onto a single nanocrystal, synergistic properties can arise that are not present in the isolated components, ranging from self-assembly to photocatalysis. While much progress was made in the late 1990s and early 2000s on the preparation of a variety of semiconductor/metal hybrids towards goals of photocatalysis, comprehensive understanding of nanoscale reactivity and energetics required the development of synthetic methods to prepare well-defined multidimensional constructs. For semiconductor nanomaterials, this was first realized in the ability to tune nanomaterial dimensions from 0-D quantum dot (QD) structures to cylindrical (NR) and branched (TP) structures by exploitation of advanced colloidal synthesis techniques and understandings of NC facet reactivities. Another key advance in this field was the preparation of "seeded" NR and TP constructs, for which an initial semiconductor QD (often CdSe) is used to "seed" the growth of a second semiconductor material (for example, CdS). These advances led to exquisite levels of control of semiconductor nanomaterial composition, shape, and size. Concurrently, many developments were made in the functionalization of these NCs with metallic nanoparticles, allowing for precise tuning of metal nanoparticle deposition position on the surface of preformed semiconductor NCs. To date, photoinduced and thermally induced methods are most widely used for this, providing access to metal-semiconductor hybrid structures functionalized with Au, Pt, Ag2S, Pd, Au/Pt, Ni, and Co nanoparticles (to name a few). With colloidal nanomaterial preparation becoming analogous to traditional molecular systems in terms of selectivity, property modulation, and compositional control, the field of nanomaterial total synthesis has thus emerged in the past decade. With a large toolbox of reactions which afford selectivity at the nanoscale developed, to date it is possible to design a wider array of materials than ever before. Only recently (the past ~ 5 years), however, has the transition from design of model systems for fundamental characterization to realization of functional materials with optimized properties begun to be demonstrated. The emphasis of chapter 1 is thus on the key advances in the preparation of metal-semiconductor hybrid nanoparticles made to date, with seminal synthetic, characterization, and application milestones being highlighted. The second chapter is focused on the synthesis and characterization of well-defined CdSe-seeded-CdS (CdSe@CdS) NR systems synthesized by overcoating of wurtzite (W) CdSe quantum dots with W-CdS shells. 1-dimensional NRs have been interesting constructs for applications such as solar concentrators, optical gains, and photocatalysis. In each of these cases, a critical step is the localization of photoexcited excitons from the light-harvesting CdS NR "antenna" into the CdSe QD seed, from which emission is primarily observed. However, effects of seed size and NR length on this process remained unexplored prior to this work. Previous work had demonstrated that, for core@shell CdSe@CdS systems, small CdSe seed sizes (< 2.8 nm in diameter) resulted in quasi-type II alignment between semiconductor components (with photoexcited electrons delocalized across the structure and holes localized in the CdSe seed), and large seed sizes (> 2.8 nm) resulted in type I alignment (with photoexcited electrons and holes localized in the CdSe seed). Through synthetic control over CdSe@CdS NR systems, materials with small and large CdSe seeds were prepared, and for each seed size, multiple NR lengths were prepared. Through transient absorption studies, it was found that band alignment did not affect the efficiency of charge localization in the CdSe core, whereas NR length had a profound effect. This work indicated that longer NRs resulted in poor exciton localization efficiencies owing to ultrafast trapping of photoexcited excitons generated in the CdS NR. Thus, with increasing rod length, poorer efficiencies were observed. This work served to highlight the ideal size range for CdSe@CdS NR constructs targeted towards photocatalysis, with ~ 40 nm NRs exhibiting the best rod-to-seed localization efficiencies. Additionally, it served to expand the understanding of exciton trapping in colloidal NC systems, allowing development of a predictive model to help guide the preparation of other nanorod based photocatalytic systems. The third chapter describes the synthesis of Au-tipped CdSe NRs and studies of the effects of selective metal nanoparticle deposition on the band edge energetics of these model photocatalytic systems. Previous studies had demonstrated ultrafast localization of photoexcited electrons in Au nanoparticles (AuNP) (and PtNP) deposited at the termini of CdSe and CdSe@CdS NR constructs. Also, for similar systems, the hydrogen evolution reaction (HER) had been studied, for which it was found that noble metal nanoparticle tips were necessary to extract photoexcited electrons from the NR constructs and drive catalytic reactions. However, in these studies, energetic trap states, generally ascribed to surface defects on the NC surface, are often cited as contributing to loss of catalytic efficiency. In this study, we found that the literature trend of assuming the band-edge energetics of the parent semiconductor NC applies to the final metal-functionalized catalyst did not present a complete picture of these systems. Through a combination of ultraviolet photoelectron spectroscopy and waveguide based spectroelectrochemistry on films of 40 nm long CdSe NRs before and after AuNP functionalization, we found that metal deposition resulted in the formation of mid-gap energy states, which were assigned as metal-semiconductor interface states. Previously these states had only been seen in single particle STS studies, and their identification in this study from complementary characterization techniques highlighted a need to further understand the nature of the interface between metal/semiconductor components for the design of photoelectrochemical systems with appropriate band alignments for efficient photocatalysis. The fourth chapter transitions from NR constructs to highly absorbing CdSe@CdS TP materials, for which a single zincblende (ZB) CdSe NC is used to seed the growth of four identical CdS arms. These arms act as highly efficient light absorbers, resulting in absorption cross sections an order of magnitude greater than for comparable NR systems. In the past, many studies have been published on the striking properties of TP nanocrystals, such as dual wavelength fluorescence, multiple exciton generation, and inherent self-assembly owing to their unique geometry. Nonetheless, these materials have not been exploited for photocatalysis, primarily owing to challenges in preparing TP from ultrasmall ZB-CdSe seed size (owing to phase instability of the zincblende crystal structure), thus preventing access to quasi-type II structures necessary for efficient photocatalysis. In this study, we successfully break through the type I/quasi-type II barrier for TP NCs, reclaiming lost ground in this field and demonstrating for the first time quasi-type II behavior in CdSe@CdS TPs through transient absorption measurements. This was enabled by new synthetic protocols for the synthesis and stabilization of ultrasmall (1.8 – 2.8 nm) ZB-CdSe seeds, as well as for the synthesis of CdSe@CdS TPs with arm lengths of 40 nm. Easily scalable, TPs were prepared on gram scales, and the quasi-type II systems showed dramatically enhanced rates of selective photodeposition of AuNP tips under ultraviolet and solar irradiation. These are promising materials for photocatalytic and solar energy applications. The fifth chapter continues with the study of CdSe@CdS TPs, and elaborates on a new method for the selective functionalization of the highly symmetrical TP construct. Previous studies had demonstrated that access to single noble metal NP tips was vital for efficient photocatalytic HER from NR constructs. However, TP materials have been notoriously difficult to selectively functionalize, owing to their symmetric nature. Using a novel photoinduced electrochemical Ostwald ripening process, we found that initially randomly deposited AuNPs could be ripened to a single, large (~ 7 nm) AuNP tip at the end of one arm of a type I CdSe@CdS TP with 40 nm arms. To demonstrate the selectivity of this tipping process, dipolar cobalt was selectively overcoated onto the AuNP tips of these TPs, resulting in dipolar Au@Co-CdSe@CdS TP nanocrystals. These particles were observed to spontaneous self-assemble into 1-D mesoscopic chains, owing to pairing of N-S dipoles of the ferromagnetic CoNPs, resulting in the first example of “colloidal polymers” (CPs) bearing bulky, tetrapod ("giant t-butyl") pendant groups. The sixth chapter elaborates further on the preparation of colloidal polymers, further extending the analogy between molecular and colloidal levels of synthetic control. One challenge in the field of colloidal science is the realization of new modes of self-assemble for compositionally distinct nanoparticles. In this work, it was found that Au@Co nanoparticle dipole strength could be systematically varied by tuning of AuNP size on CdSe@CdS nanorods/tetrapods. In the first example of a colloidal analogue to reactivity ratios observed for traditional chain growth polymerization systems, highly disparate AuNP tip sizes (and thus final Au@Co NP dipole strength) were found to result in segmented colloidal copolymers upon dipolar self-assembly, whereas similar AuNP tip sizes ultimately led to random dipolar assemblies. Clearly visualized through incorporation of NR and TP sidechains into these colloidal polymers, this study presented a compelling case for continued exploration of colloidal analogues to traditional molecular levels of synthetic control.