Terahertz Response of Excitons in Nanorod Heterostructures

Quantum-confined systems are one of the most promising ways to enable us to control a material's interactions with light. Nanorods in particular offer the right dimensions for exploring and manipulating the terahertz region of the spectrum. In this thesis, we model excitons confined inside a nanorod using the envelope function approximation. A region-matching transfer matrix method allows us to simulate excitonic states inside arbitrary heterostructures grown along the length of the rod. We apply the method to colloidal CdSe rods 70 nm in length and under 10 nm in diameter, capped with ligands of DDPA and pyridine. We extend past studies on these types of rods by taking into account their dielectric permittivity mismatch. Compared to previous calculations and experimentally measured terahertz absorption, we predict a higher energy main 1S$z$ to 2P$z$ transition peak. This indicates that the rods are likely larger in diameter than previously thought. We also investigate a nanorod with GaAs/Al$_{0.3}$Ga$_{0.7}$As coupled double dots. The excitonic transitions were found to be manipulable by varying the strength of an applied electric field. We employ quasi-static state population distributions to simulate the effects of exciton relaxation from optically active states to dim ground states. A critical value of the applied field, corresponding to the exciton binding energy of ~18 meV, was found to dramatically alter the terahertz absorption due to state mixing. Above this critical field, more nuanced shifts in transition energies were observed, and gain from radiative relaxation to the ground state is predicted.

Measurements of organic complexation of iron during the CARUSO-EISENEX experiment

The speciation of strongly chelated iron during the 22-day course of an iron enrichment experiment in the Atlantic sector of the Southern Ocean deviates strongly from ambient natural waters. Three iron additions (ferrous sulfate solution) were conducted, resulting in elevated dissolved iron concentrations (Nishioka, J., Takeda, S., de Baar, H.J.W., Croot, P.L., Boye, M., Laan, P., Timmermans, K.R., 2005, Changes in the concentration of iron in different size fractions during an iron enrichment experiment in the open Southern Ocean. Marine Chemistry, doi:10.1016/j.marchem.2004.06.040) and significant Fe(II) levels (Croot, P.L., Laan, P., Nishioka, J., Strass, V., Cisewski, B., Boye, M., Timmermans, K.R., Bellerby, R.G., Goldson, L., Nightingale, P., de Baar, H.J.W., 2005, Spatial and Temporal distribution of Fe(II) and H2O2 during EisenEx, an open ocean mescoscale iron enrichment. Marine Chemistry, doi:10.1016/j.marchem.2004.06.041). Repeated vertical profiles for dissolved (filtrate < 0.2 µm) Fe(III)-binding ligands indicated a production of chelators in the upper water column induced by iron fertilizations. Abiotic processes (chemical reactions) and an inductive biologically mediated mechanism were the likely sources of the dissolved ligands which existed either as inorganic amorphous phases and/or as strong organic chelators. Discrete analysis on ultra-filtered samples (< 200 kDa) suggested that the produced ligands would be principally colloidal in size (> 200 kDa-< 0.2 µm), as opposed to the soluble fraction (< 200 kDa) which dominated prior to the iron infusions. Yet these colloidal ligands would exist in a more transient nature than soluble ligands which may have a longer residence time. The production of dissolved Fe-chelators was generally smaller than the overall increase in dissolved iron in the surface infused mixed layer, leaving a fraction (about 13-40%) of dissolved Fe not bound by these dissolved Fe-chelators. It is suggested that this fraction would be inorganic colloids. The unexpected persistence of such high inorganic colloids concentrations above inorganic Fe-solubility limits illustrates the peculiar features of the chemical iron cycling in these waters. Obviously, the artificial about hundred-fold increase of overall Fe levels by addition of dissolved inorganic Fe(II) ions yields a major disruption of the natural physical-chemical abundances and reactivity of Fe in seawater. Hence the ensuing responses of the plankton ecosystem, while in itself significant, are not necessarily representative for a natural enrichment, for example by dry or wet deposition of aeolian dust. Ultimately, the temporal changes of the Fe(III)-binding ligand and iron concentrations were dominated by the mixing events that occurred during EISENEX, with storms leading to more than an order of magnitude dilution of the dissolved ligands and iron concentrations. This had strongest impact on the colloidal size class (> 200 kDa-< 0.2 µm) where a dramatic decrease of both the colloidal ligand and the colloidal iron levels (Nishioka, J., Takeda, S., de Baar, H.J.W., Croot, P.L., Boye, M., Laan, P., Timmermans, K.R., 2005, Changes in the concentration of iron in different size fractions during an iron enrichment experiment in the open Southern Ocean. Marine Chemistry, doi:10.1016/j.marchem.2004.06.040) was observed.

Inorganic colloid chemistry,

I. The collidal elements.--II. The hydrous oxides and hydroxides.--III. The colloidal salts.

The Harvey lectures : delivered under the auspices of the Harvey Society of New York, 1913-1914 /

Includes bibliographical references.

Synthesis of Silver Nanoparticle Based Conductive Inks for Additively Manufactured Electronics

Thesis (Master's)--University of Washington, 2016-06

Pseudo-ternary phase diagrams of aqueous mixtures of Quil A, cholesterol and phospholipid prepared by the lipid-film hydration method

Pseudo-ternary phase diagrams of the polar lipids Quil A, cholesterol (Chol) and phosphatidylcholine (PC) in aqueous mixtures prepared by the lipid film hydration method (where dried lipid film of phospholipids and cholesterol are hydrated by an aqueous solution of Quil A) were investigated in terms of the types of particulate structures formed therein. Negative staining transmission electron microscopy and polarized light microscopy were used to characterize the colloidal and coarse dispersed particles present in the systems. Pseudo-ternary phase diagrams were established for lipid mixtures hydrated in water and in Tris buffer (pH 7.4). The effect of equilibration time was also studied with respect to systems hydrated in water where the samples were stored for 2 months at 4degreesC. Depending on the mass ratio of Quil A, Chol and PC in the systems, various colloidal particles including ISCOM matrices, liposomes, ring-like micelles and worm-like micelles were observed. Other colloidal particles were also observed as minor structures in the presence of these predominant colloids including helices, layered structures and lamellae (hexagonal pattern of ring-like micelles). In terms of the conditions which appeared to promote the formation of ISCOM matrices, the area of the phase diagrams associated with systems containing these structures increased in the order: hydrated in water/short equilibration period < hydrated in buffer/short equilibration period < hydrated in water/prolonged equilibration period. ISCOM matrices appeared to form over time from samples, which initially contained a high concentration of ring-like micelles suggesting that these colloidal structures may be precursors to ISCOM matrix formation. Helices were also frequently found in samples containing ISCOM matrices as a minor colloidal structure. Equilibration time and presence of buffer salts also promoted the formation of liposomes in systems not containing Quil A. These parameters however, did not appear to significantly affect the occurrence and predominance of other structures present in the pseudo-binary systems containing Quil A. Pseudo-ternary phase diagrams of PC, Chol and Quil A are important to identify combinations which will produce different colloidal structures, particularly ISCOM matrices, by the method of lipid film hydration. Colloidal structures comprising these three components are readily prepared by hydration of dried lipid films and may have application in vaccine delivery where the functionality of ISCOMs has clearly been demonstrated. (C) 2003 Elsevier B.V. All rights reserved.

A comparison of pseudo-ternary diagrams of aqueous mixtures of Quil A, cholesterol and phospholipid prepared by lipid-film hydration and dialysis

Pseudo-ternary diagrams for Quil A, phospholipid (phosphatidylcholine (PC) or phosphatidylethanolamine (PE)) and cholesterol were established in order to identify combinations that result in the formation of immune-stimulating complex (ISCOM) matrices and other colloidal structures produced by these three components in aqueous systems following lipid-film hydration or dialysis (methods that can be used to produce ISCOMs). In addition, the effect of equilibration time (1 month at 4degreesC) on the structures formed by the various combinations of the three components was investigated. Depending on the ratio of Quil A, cholesterol and phospholipid, different colloidal particles, including ISCOM matrices, liposomes and ring-like micelles, were found irrespective of the preparation method used. In contrast, worm-like micelles were only observed in systems prepared by lipid-film hydration. For samples prepared by dialysis, ISCOM matrices were predominantly found near the Quil A apex of the pseudo-ternary diagram (> 50% Quil A). On the other hand, for samples prepared by lipid-film hydration, ISCOM matrices were predominantly found near the phospholipid apex of the pseudo-ternary diagram (> 50% phospholipid). The regions in the pseudo-ternary diagrams in which ISCOM matrices were observed increased following an extended equilibration time, particularly for samples prepared by lipid-film hydration. Differences were also observed between pseudoternary diagrams prepared using either PE or PC as phospholipids.

Rare earth element geochemistry of Late Devonian reefal carbonates, canning basin, Western Australia: Confirmation of a seawater REE proxy in ancient limestones

Rare earth element and yttrium (REE+Y) concentrations were determined in 49 Late Devonian reefal carbonates from the Lennard Shelf, Canning Basin, Western Australia. Shale-normalized (SN) REE+Y patterns of the Late Devonian samples display features consistent with the geochemistry of well-oxygenated, shallow seawater. A variety of different ancient limestone components, including microbialites, some skeletal carbonates (stromatoporoids), and cements, record seawater-like REE+Y signatures. Contamination associated with phosphate, Fe-oxides and shale was tested quantitatively, and can be discounted as the source of the REE+Y patterns. Co-occurring carbonate components that presumably precipitated from the same seawater have different relative REE concentrations, but consistent REE+Y patterns. Clean Devonian early marine cements (n = 3) display REE+Y signatures most like that of modern open ocean seawater and the highest Y/Ho ratios (e.g., 59) and greatest light REE (LREE) depletion (average Nd-SN/Yb-SN = 0.413, SD = 0.076). However, synsedimentary cements have the lowest REE concentrations (e.g., 405 ppb). Non-contaminated Devonian microbialite samples containing a mixture of the calcimicrobe Renalcis and micritic thrombolite aggregates in early marine cement (n = 11) have the highest relative REE concentrations of tested carbonates (average total REE = 11.3 ppm). Stromatoporoid skeletons, unlike modern corals, algae and molluscs, also contain well-developed, seawater-like REE patterns. Samples from an estuarine fringing reef have very different REE+Y patterns with LREE enrichment (Nd-SN/Yb-SN > 1), possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged LREE from a nearby riverine input source. Hence, Devonian limestones provide a proxy for marine REE geochemistry and allow the differentiation of co-occurring water masses on the ancient Lennard Shelf. Although appropriate partition coefficients for quantification of Devonian seawater REE concentrations from out data are unknown, hypothetical Devonian Canning Basin seawater REE patterns were obtained with coefficients derived from modern natural proxies and experimental values. Resulting Devonian seawater patterns are slightly enriched in LREE compared to most modem seawaters and suggest higher overall REE concentrations, but are very similar to seawaters from regions with high terrigenous inputs. Our results suggest that most limestones should record important aspects of the REE geochemistry of the waters in which they precipitated, provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high, non-seawater-like REE contents. Hence, we expect that many other ancient limestones will serve as seawater REE proxies, and thereby provide information on paleoceanography, paleogeography and geochemical evolution of the oceans. Copyright (C) 2004 Elsevier Ltd.

Energy transfer dynamics of nanocrystal-polymer composites

Steady-state and time-resolved photoluminescence spectroscopy are used to examine the photoluminescent properties of nanocrystal-polymer composites consisting of colloidal PbS nanocrystals blended with poly(2-methoxy-5(2-ethylhexyloxy)-p-phenylene vinylene). Quenching of the emission from the conjugated polymer due to the PbS nanocrystals is observed along with band edge emission from the ligand capped PbS nanocrystals. A decrease in the photoluminescence lifetime of MEH-PPV is also observed in the thin film nanocrystal-polymer composite materials. Photoluminescence excitation spectroscopy of the PbS nanocrystal emission from the composite shows features attributed to MEH-PPV providing evidence of a Forster transfer process.

W/O microemulsions for ocular delivery: Evaluation of ocular irritation and precorneal retention

Water-in-oil microemulsions (w/o ME) capable of undergoing a phase-transition to lamellar liquid crystals (LC) or bicontinuous ME upon aqueous dilution were formulated using Crodarnol EO, Crill 1 and Crillet 4, an alkanol or alkanediol as cosurfactant and water. The hypothesis that phase-transition of ME to LC may be induced by tears and serve to prolong precomeal retention was tested. The ocular irritation potential of components and formulations was assessed using a modified hen's egg chorioallantoic membrane test (HET-CAM) and the preocular retention of selected formulations was investigated in rabbit eye using gamma scintigraphy. Results showed that Crill 1, Crillet 4 and Crodamol EO were non-irritant. However, all other cosurfactants investigated were irritant and their irritation was dependent on their carbon chain length. A w/o ME formulated without cosurfactant showed a protective effect when a strong irritant (0.1 M NaOH) was used as the aqueous phase. Precorneal clearance studies revealed that the retention of colloidal and coarse dispersed systems was significantly greater than an aqueous solution with no significant difference between ME systems (containing 5% and 10% water) as well as o/w emulsion containing 85% water. Conversely, a LC system formulated without cosurfactant displayed a significantly greater retention compared to other formulations. (c) 2005 Elsevier B.V. All rights reserved.

Preparation of immuno-stimulating complexes (ISCOMs) by ether injection

preparation of liposomes, as a new, continuous and potentially scaleable method for the preparation of ISCOMs. Phosphatidylcholine (PC) and cholesterol (Chol) were dissolved in ether, which was injected into an aqueous solution, maintained at 55 degrees C, containing Quil A. The influences of the following variables on ISCOM formation were investigated: ratio of PC:Quil A:Chol used, pumping rate, total lipid mass and concentration of buffer salts and Quil A in the aqueous phase. All samples were characterized by negative stain transmission electron microscopy, photon correlation spectroscopy and sucrose ultracentrifugation gradient. It was demonstrated that ISCOMs could be produced by this method but the homogeneity of the preparation was influenced by the conditions used. Homogeneous ISCOM preparations were consistently produced only when the weight ratio of PC:Quil A:Chol was 5:3:2 with a total lipid mass of 20 mg, the Quil A dissolved in a 0.01 M phosphate buffer at a concentration of 6 mg in 4 ml, and the ether solution injected into the warmed buffer solution at a rate of 0.2 ml/min. Changing any of these variables resulted in more heterogeneous preparations in which ISCOMs typically co-existed with other colloidal structures such as worm-like and helical micelles, liposomes, lamellae and lipidic particles. (C) 2005 Elsevier B.V. All rights reserved.

Time-resolved photoluminescence spectroscopy of ligand-capped PbS nanocrystals

PbS nanocrystals are synthesized using colloidal techniques and have their surfaces capped with oleic acid. The absorption band edge of the PbS nanocrystals is tuned between 900 and 580 nm. The PbS nanocrystals exhibit tuneable photoluminescence with large non-resonant Stokes shifts of up to 500 mcV. The magnitude of the Stokes shift is found to be dependent upon the size of PbS nanocrystals. Time-resolved photoluminescence spectroscopy of the PbS nanocrystals reveals that the photouminescence has an extraordinarily long lifetime of 1 mus. This long fluorescence lifetime is attributed to the effect of dielectric screening similar to that observed in other IV-VI semiconductor nanocrystals.

Quantitative analysis and characterization of biofunctionalized fluorescent silica particles

A strategy for the production and subsequent characterization of biofunctionalized silica particles is presented. The particles were engineered to produce a bifunctional material capable of both (a) the attachment of fluorescent dyes for particle encoding and (b) the sequential modification of the surface of the particles to couple oligonucleotide probes. A combination of microscopic and analytical methods is implemented to demonstrate that modification of the particles with 3-aminopropyl trimethoxysilane results in an even distribution of amine groups across the particle surface. Evidence is provided to indicate that there are negligible interactions between the bound fluorescent dyes and the attached biomolecules. A unique approach was adopted to provide direct quantification of the oligonucleotide probe loading on the particle surface through X-ray photoelectron spectroscopy, a technique which may have a major impact for current researchers and users of bead-based technologies. A simple hybridization assay showing high sequence specificity is included to demonstrate the applicability of these particles to DNA screening.

Saponins from Quillaja saponaria Molina: Isolation, Characterization and Ability to Form Immuno Stimulatory Complexes (ISCOMs)

ISCOMs have received much attention as vaccine adjuvants due to their immunostimulatory effects. They are colloidal particles typically comprised of phospholipids, cholesterol and Quil A, a crude mixture of saponins extracted from the bark of Quillaja saponaria Molina. We have previously shown that ISCOMs can be prepared by ether injection wherein an ether solution of phospholipids and cholesterol in a mass ratio of 5:2 is injected into a solution of Quil A at a mass ratio of 7 lipids: 3 Quil A. The aim of this study was firstly to isolate and characterise discrete fractions of Quil A and secondly to investigate which of these fractions were able to form ISCOMs by the method of ether injection. Six fractions of Quil A were isolated by semi-preparative reverse phase high performance liquid chromatography (RP-HPLC) and characterised by analytical HPLC, liquid chromatography tandem mass spectrometry (LC-MS) and the qualitative Liebermann- Burchard and Molisch tests for triterpenoids and carbohydrates respectively. ISCOMs were subsequently prepared from the isolated fractions by the method of ether injection and the resulting preparations characterized by photon correlation spectroscopy (PCS) and negative stain transmission electron microscopy (TEM). The molecular weights of the major compounds in the fractions ranged from ∼1200 to ∼2300 Da; all fractions tested positive for triterpenoids and saccharides and four of the fractions were identified as QS-7, QS-17, QS-18 and QS-21 by analysis (LC-MS and analytical HPLC). Injection of ether solutions of lipids into aqueous solutions of QS-17, QS-18 or QS-21 all resulted in homogeneous ISCOM dispersions. The combination of lipids and QS-7 by ether injection produced lamellae and liposomes as the prominent structures and a minor amount of ISCOMs. The remaining two hydrophilic, low molecular weight fractions of Quil A did not produce ISCOMs, instead liposomes and helical structures predominated in the samples.

Influence of nanowire density on the shape and optical properties of ternary InGaAs nanowires

We have synthesized ternary InGaAs nanowires on (111)B GaAs surfaces by metal-organic chemical vapor deposition. Au colloidal nanoparticles were employed to catalyze nanowire growth. We observed the strong influence of nanowire density on nanowire height, tapering, and base shape specific to the nanowires with high In composition. This dependency was attributed to the large difference of diffusion length on (111)B surfaces between In and Ga reaction species, with In being the more mobile species. Energy dispersive X-ray spectroscopy analysis together with high-resolution electron microscopy study of individual InGaAs nanowires shows large In/Ga compositional variation along the nanowire supporting the present diffusion model. Photoluminescence spectra exhibit a red shift with decreasing nanowire density due to the higher degree of In incorporation in more sparsely distributed InGaAs nanowires.