Thesis advisor: Dunwei Wang / Metal nanocrystals with size and shape control have great potential in heterogeneous catalysis. Controllable encapsulation of well-defined metal nanoparticles into the novel porous materials results in new multifunctional nanomaterials. The core-shell nanostructure can enhance the selectivity, durability, or reactivity of the catalysts and even provide additional functionalities. Metal-organic frameworks (MOFs) are a class of novel crystalline nanoporous materials, with well-defined pore structures and distinctive chemical properties. Using MOFs as the encapsulating porous materials has drawn great interest recently due to their tunable structures and properties. However, it could be challenging to grow another porous material layer on metal surface due to the unfavorable interfacial energy. In this work we develop a new concept of colloidal synthesis to synthesize the metal@MOF core-shell nanostructures, in which a layer of self-assembled molecules directed the growth and alignment between two materials. Surfactant cetyltrimethylammonium bromide (CTAB) is designated to facilitate the overgrowth of MOF onto metal surface, and an alignment between the {100} planes of the metal and {110} planes of the MOF can be observed. By utilizing the same concept, a third layer of mesoporous silica could also be coated on the MOF shell with assistance of CTAB. And our method could be a general strategy to fabricate multiple-layer MOF materials. / Thesis (MS) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Our work addresses a novel biocompatible plasmon-enhanced nanostructure approach based on the combination of metal nanoparticles, light emitting polymer-based nanostructures, and scalable cellulose nanofiber templates via a one-step facile electrospinning process that can easily be applied to biomedical devices. In collaboration with the Team of Prof. Lee Goldstein in the Boston University medical campus, we demonstrated light emission from small-size (below 200nm) polymer nanoparticles coupled to plasmonic nanoparticles and to light-emitting biocompatible molecules. In order to fully demonstrate the potential of our novel plasmonic nanostructures we developed Magnetic resonance imaging (MRI) reagent doped Polycaprolactone (Core)-Polyethylene glycol (shell) core-shell nanoparticles and studied their size distribution and dispersion properties in a phosphate buffered saline solution. Our materials were optimized in order to obtain no aggregation of the nanoparticles in solution. The presence of MRI reagent in nanoparticles were demonstrated via Inversion Recovery Sequences (IR) by characterizing the different T1 relaxation times. The concentration of Gd in the nanoparticles dispersion was estimated with different dilution of Gd commercial reagent as a reference. In addition, we combined facile electrospinning fabrication with top down nano-deposition and demonstrated a novel and scalable plasmonic resonant medium for rapid and reliable Raman scattering sensing of molecular monolayers and bacteria. Specifically, aided by PCA multivariate data analysis techniques, we demonstrated fingerprinting Surface Enhanced Raman Scattering (SERS) spectra of different bacteria strains (E. Coli K12, E. coli BL21 (DE3) and E. coli DH 5α) entrapped in our novel plasmonic networks. Finally, in this thesis we have also addressed the development of novel, Si-compatible and largely tunable plasmonic materials for biosensing applications in the mid-infrared spectral range and developed a novel type of transparent conductive oxide based on the Indium Silicon Oxide (ISO) material (Indium Silicon Oxide) that features enhanced surface smoothness and thermal stability compared to Indium tin oxide (ITO) and Titanium nitride (TiN) alternative plasmonic materials. In collaboration with our collaborators at Columbia University, we demonstrated the tunability of near-field plasmonic resonances from 1.8 to 5.0 μm as a function of different annealing temperature. This work provides an enabling first-step towards the development of novel Si-compatible materials with tunable plasmon resonances for metamaterials and sensing devices that operate across the infrared spectrum. / 2019-07-02T00:00:00Z

The objective of this Ph.D. study is to explore an important and fertile research topic on the methods for synthesis of nanomaterials by homogeneous nonaqueous solution phase reaction. Research in this work focuses on synthesizing several kinds of nanomaterials in different environments and structure, including spherical nanoparticles, nanowires and core-shell structure composites We first synthesized metallic nanomaterials in this system, such as ~10 nm Fe nanoparticles, ~6 nm Au nanoparticles, and ~100 nm Bi nanoparticles, this system are the preparation for the following studies. Secondly, we synthesized bimetallic nanomaterials in this system, such as Fe50Co50 alloy and Bi doped with Mn. For FeCo alloy, after annealing at 500 °C, a pure phase of Fe50Co50 was obtained. And we first synthesized the nanowires of bismuth doped with manganese. By studying intermediates at different temperatures during the growth process of nanowires, the evolution of the crystallization of metallic products and the mechanism of the formation of the nanowires are investigated. Thirdly, we synthesized core-shell structure nanocomposites, including either gold as the shell or polymer as the shell. Au-coated magnetic Fe nanoparticles have been successfully synthesized by partial replacement reaction in a polar aprotic solvent with about 11 nm core of Fe and about 2.5 nm shell of Au. HRTEM images show clear core-shell structure with different crystal lattices from Fe and Au. SQUID magnetometry reveals that particle magnetic properties are not significantly affected by the overlayer of a moderately thick Au shell. The Aucoated particles exhibit a surface plasmon resonance peak that red-shifts from 520 to 680 nm. And Poly (Vinyl Pyrolidone) (PVP) coated iron nanoparticles also have been successfully synthesized in a polar aprotic solvent, which shows the welldefined core-shell structures. In this approach, Poly (Vinyl Pyrolidone) (PVP) was employed as the coating polymer directly coated on metallic core (iron) nanoparticles. In this work, a combination of TEM (transmission electron microscopy), EDS (Energy disperse X-ray spectroscopy), XRD (X-ray powder diffractometry), ICP (inductively-coupled plasma spectrometer), TGA (Thermogravimetric analysis), UV-visible absorption spectroscopy, IR (infrared) spectroscopy and SQUID magnetometry (Superconducting Quantum Interference Device) were employed to characterize the morphology, structure, composition and magnetic properties of the products. In summary, this Ph.D. study successfully and systematically synthesized several kinds of nanocomposites in a system. The synthetic procedure is simple, economic and easily scaled-up for further applications. And many techniques were employed to characterize the products.

Thesis advisor: Chia-kuang Frank Tsung / Pt-based alloy and core-shell nanoparticles have been intensively studied to regulate its size and shape. It has known that these nanoparticles show enhanced catalytic activity in various important fields such as heterogeneous catalysis, and electrochemical energy storage including fuel cells and metal-air batteries. Here, we report a facile hydrothermal synthesis of sub-10 nm PdPt alloy and sub-20 nm Au@PdPt core-shell structures. By using a mild reducing agent in aqueous solution, metal precursors are co-reduced. Specific gases are introduced during the synthesis to optimize the reaction conditions. The PdPt alloy and Au@PdPt core-shell nanostructures were characterized and confirmed by TEM, HRTEM, EDS, ICP-OES and XRD. The resulting PdPt and Au@PdPt particles are monodispersed single crystalline and octahedral shape enclosed by (111) facets. The electrocatalytic activity for the oxidation of formic acid was tested. It was found that the catalytic activity toward the formic acid oxidation of Au@PdPt core-shell particles were much higher than those of PdPt alloy particles. In addition, Pt-rich compositions were the most active in both PdPt alloy and Au@PdPt core-shell nanoparticles. Further studies on thinner alloy-shell core-shell nanoparticles reveal that there is a volcano-curve relationship between the lattice strain strength related to alloy-shell thickness and the catalytic performance. It is proposed that there are three key parameters that can determine the catalytic activity: the alloy composition, the presence of the gold core, and the thickness of alloy-shell. / Thesis (MS) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Vapor grown carbon nanofibers (VGCNFs) developed in 1980s are being widely used for reinforcing composites. Carbon nanotubes (CNTs) discovered in early 1990 can be classified as single wall carbon nanotubes (SWNTs), double wall carbon nanotube (DWNTs) and multi wall carbon nanotubes (MWNTs) depending on the number of grapheme layer forming the carbon nanotube. Polyacrylonitrile (PAN), a commercially important polymer is a predominant precursor for carbon fiber. Carbonized and activated PAN/SWNT films can find application as electrochemical supercapacitor electrodes. This study is focused on the structure, processing and properties of polyacrylonitrile/carbon nanotube (CNT) composite films. PAN/SWNT (60/40) composite film have been processed with unique combination of tensile strength, modulus, electrical conductivity, dimensional stability, low density, solvent resistance, and thermal stability. PAN molecular motion above the glass transition temperature (Tg) in the composite film is significantly suppressed, resulting in high PAN/SWNT storage modulus above Tg. The specific modulus of PAN/VGCNF composite films is consistent with the predictions of the Halpin-Tsai equation up to 20% VGCNF loading. The magnitude of modulus and other property enhancement is reduced as the nanofiber loading is increased (up to 40%). Further increase in nanofiber loading (> 40%) in composite results in modulus and tensile strength lower than those of control PAN. Electrical percolation was observed at 3.1 vol% VGCNF loading. PAN/CNT composite films were processed using SWNTs, DWNTs, MWNTs and VGCNFs to study the effect of various nanotubes on the composite properties. PAN/CNT films have been characterized by wide angle X-ray diffraction (WAXD), Raman spectroscopy, and scanning as well as transmission electron microscopy. Films have also been characterized for electrical conductivity, tensile and dynamic mechanical properties. Mechanical property results have been analyzed in terms of the nanotube surface area determined by nitrogen gas adsorption. PAN/CNT composite films and fibers are characterized using solid state 1HNMR spin lattice relaxation time (T1). With the addition of nanotubes, the T1 values for the PAN matrix generally decreased, and the reduction mechanism is discussed. The optical anisotropy of SWNT in PAN/SWNT composites was observed in their polarized infrared spectra and analyzed using the effective medium theory.

No description available.

Ce travail de thèse a été consacré au développement d’un système multicouche constitué de nanoparticules dopées par des ions terres rares (le cœur), entourées d’une première couche cristalline non dopée, permettant de préserver les propriétés optiques du cœur. Une coquille de silice mésoporeuse est ensuite déposée, permettant l’incorporation d’un photosensibilisateur (ZnPc) via les pores de la couche de silice pour une application thérapeutique : la photothérapie dynamique. Différentes matrices ont été étudiées à savoir Y2O3, KY3F10 et NaYF4. Ces matrices ont été codopées Yb3+/Er3+ afin d’obtenir des émissions dans le visible sous l’effet d’une excitation infrarouge (upconversion), le but ultime étant d’exciter le ZnPc in situ. Chacune des matrices a été caractérisée d’un point de vue structural et morphologique dans une première partie, et d’un point de vue spectroscopique dans une deuxième partie. La structure cœur-coquille cristalline renforce l’émission rouge issue du niveau 4F9/2 de l’Er, effet déduit de l’analyse des spectres et de la dynamique de luminescence.La détection de l’oxygène singulet a été réalisée par le protocole de « bleaching » en présence ou pas du ZnPc en évaluant l’intensité de fluorescence de l’ABDA. / This work has been dedicated to the development of a multistep system composed by rare earths doped nanoparticles (core), enclosed by a first undoped crystalline layer (core-shell), serving as protection of the optical properties of the core. Within a shell of mesoporous silica allowing the loading of the photosensitizer (ZnPc) via the pores of the shell of silica for a therapeutic application: the photodynamic therapy. Various lattices were studied namely Y2O3, KY3F10 and NaYF4. These lattices were codoped with Yb3+ and Er3+ ions to obtain emissions in the visible under an infrared excitation (up conversion), the ultimate purpose being to excite in situ ZnPc. Each of these lattices was characterized from a structural and morphological point of view in the first part and, in the second part, spectroscopic studies are developed. The core-shell enhances the red emission stemming from the level 4F9/2 of Er, effect deduced from the analysis of spectra and the dynamics of luminescence. The detection of the singlet oxygen was realized in vitro by the study of the bleaching of ABDA fluorescence. The comparison of the results for nanoparticles loaded with ZnPc and unloaded ones allows demonstrating the generation of singlet oxygen by exciting in the infrared region of the spectra thanks to the efficient upconversion processes occurring in the rare earth doped materials.

Rotationally averaged polarizabilities and intrinsic electric dipole moments of sodium clusters are measured and reported. The experimental method is a molecular beam deflection. Our precision is the highest (<5%) and the range of the cluster sizes is the broadest to date (Na₁₀ ∼ Na₃₀₀). Compared to the earlier measurements, our data covers all sizes with no gaps up to the largest cluster. The fine structure in the polarizability curve is previously unobserved. We have carefully ruled out several possible explanations. And we find an earlier existing theory could explain the facts but will lead to magic numbers which were not seen in some previous experiments. A detailed theory is needed to understand the behaviors we see. Intrinsic electric dipole moments (EDM) of sodium clusters are probed to answer the intriguing question: Do metal clusters develop electric dipole moments like molecules? Some theories have predicted the existence of EDM in ground state sodium clusters and gave their magnitudes. We put upper bounds on the EDM of sodium clusters and find that they are orders of magnitude smaller than the predictions. This provokes an interesting question: how can one define metallicity in metal clusters? Our measurements are performed at cryogenic temperature 20 Kelvin. At this temperature the clusters are believed to be in their vibronic ground states.

Ce travail a pour objectif la fabrication, en épitaxie par jets moléculaires, de nanofils coeurcoquilleà base de GaAs et AlGaAs déposés sur des substrats Si(111), en vue de réaliser desréseaux de fils pour de nouvelles cellules solaires, et pour des fils photoniques permettant uneapproche bottom-up d’émetteurs de photons uniques.La première partie de ce travail est une étude systématique des paramètres clés qui contrôlent lacroissance uni-dimensionnelle de fils GaAs élaborés par un mécanisme vapeur-liquide-solideauto-catalysé, à savoir le rapport des flux As/Ga, la température du substrat, et la vitesse decroissance.La seconde partie se concentre sur la croissance et la caractérisation de fils GaAs recouvertsd’une coquille d’alliages AlGaAs (35% Al) afin de s’affranchir des recombinaisons de surface.Ces coquillesde AlGaAs sont fabriquées en conditions riche-As (rapport As/Ga > 10) afin deconsommer les gouttes de catalyseur gallium et de promouvoir une croissance radiale (le taux decroissance maximal axial/radial est égal à 6). Diverses caractérisations optiques sont réalisées àbasse température sur ces ensembles de fils : cathodoluminescence, photoluminescence etspectroscopie résolue en temps. L’intensité de luminescence et la durée de vie des porteursaugmentent fortement avec la présence de la coquille : une épaisseur de 7 nm de cette dernièreest suffisante pour optimiser la passivation des nanofils et supprimer les recombinaisons liéesaux états de surface. Une fine couche extérieure de GaAs est nécessaire pour éviter touteoxydation de la coquille d’alliage AlGaAs.De plus, grâce à des mesures de CL résolues spatialement, les longueurs de diffusion desexcitons dans ces fils ont été obtenues, allant de 0.7 μm à 1.5 μm pour des épaisseurs decoquilles comprises entre 20 et 50 nm. Des valeurs plus petites sont mesurées pour des coquillesplus épaisses, ce qui tend à montrer l’introduction de défauts dans l’alliage qui pourraientlimiter la qualité de l’interface. Le décalage en énergie de l’émission fournit des informationssur la génération de contraintes dans ces fils coeur-coquille et sur le champ piézo-électrique quien découle. / This report focuses on the fabrication of GaAs nanowires and GaAs/AlGaAs core-shellstructures by molecular beam epitaxy, deposited on Si (111) substrates in order to providearrays of wires for innovative solar cells and bottom-up photonic wires for efficient singlephoton emitters.The first part of this work is a systematic study of the key parameters which control the onedimensionalgrowth of bare GaAs NWs with a self-assisted vapor-liquid-solid growth process,namely the As-to-Ga flux ratio, the substrate temperature, and the deposition rate.The second part concentrates on the growth and characterization of GaAs wires covered with ashell of AlGaAs alloy (35 % Al) in order to get rid of the surface recombinations. These shellswere fabricated under As-rich condition with ratio As/Ga >10 in order to consume the Gadropletscompletely and to promote a radial growth. The obtained axial-to-radial growth ratio is6. The optical characterizations on ensemble were carried out at low temperature via thecathodoluminescence (CL), photoluminescence (PL), and time-resolved PL measurements. Theresults show that the lifetime of carriers and luminescence intensity increase significantly withshell coverage. About 7 nm thick shell is enough to optimize the passivation and suppress thesurface state recombination. A thin outer cap of GaAs is required in order to prevent someoxidation of the AlGaAs alloy shell.In addition, the exciton diffusion lengths of these NWs, studied via the spatially resolved CL,are in the range of 0.7 - 1.5 μm for NWs with shell thicknesses between 20 - 50 nm. Thesevalues are smaller for thicker shells due to the defect formation, leading to limit the quality ofcore-shell interface. The shift in optical emission experiments provides the information of thestrain generation of core-shell when we vary the shell thickness. The piezoelectric field wasnoticed in these samples.

The aims of this study were to form uncompressed thermobonded 3D wool nonwoven shell structures in one continuous process, and to study the controlling factors that govern this process. Lack of bonding between wool fibres and between wool and thermoplastic fibres was attributed to the wool fibre's low surface energy because of the lipids on the outer surface of wool fibres (epicuticle). To overcome this problem, three different surface treatments were investigated; chlorination, Hercosett and plasma. The purpose of these treatments was to raise the surface energy of wool fibres by bond scission and the introduction of new functional polar groups and ablation of the outer lipid layer or membrane. For thermobonding with wool fibres, low melting nylon fibres were chosen because of their high polarity and chemical compatibility with wool fibres. SEM, BSM and ESEM imaging techniques as well as tensile strength testing for single fibres, pair bonded samples and 3D nonwoven shells were used to assess the samples. Results have shown that it is possible to thermobond wool and nylon fibres as 3D shell structures, given that wool fibres are treated appropriately and the bonding temperature is controlled properly. Moreover, it has been found that, for pair bonded samples, the wrapping angle and the bonding angle have significant effects on the tensile strength and number of bonding points. Hercosett treated wool fibres yielded the strongest bonds with nylon fibres followed by plasma, chlorinated and untreated fibres.