Liquid crystals (LCs) are an interesting class of materials that are attracting significant attention due to their ever-growing applications in a wide variety of fields such as liquid crystal display (LCD) technology, materials science and bioscience. In recent years, along with the developments of materials at the nanoscale, doping LCs with nanoparticles (NPs) has emerged as a very promising approach for improving LC properties. Nanoparticle additives can introduce novel effects on optical and electro-optical properties of nematic liquid crystals (N-LCs), such as altered molecular alignment, faster response time and increased efficiency. This thesis studies the impacts that the inclusion of metallic NPs made of gold or semiconductor CdSe quantum dots (QDs), have on optical and electro-optical properties of N-LCs. Using polarized optical microscopy and detailed capacitance and transmittance measurements of nematic mixtures in electro-optic test cells, characteristics such as optical texture, phase transition temperatures, switching voltages and dielectric anisotropy are investigated in pure as well as doped samples. Surface ligands in NPs and their chemical functionalization play an important role in the LC-NP interactions, largely by determining the dispersibility of NPs and stability of the nanocomposites. One important objective of this thesis is to investigate and prepare a series of gold nanoparticles (Au NPs) with specially formulated robust coatings that maximizes solubility and stability in LC medium. Silanization of NPs is developed as a method to overcome the stability challenge. The functionalization of silanized NPs with aliphatic ligands or liquid crystalline molecules, provides chemically and thermally stable NPs with hydrophobic and structurally compatible surfaces required for dispersion in N-LCs. After complete characterization the synthesized particles are used to make the new nematic nanocomposites. By analysis of the structure-property relationships governing LC-nanomaterial composites and by comparison of new results and data from previous studies on other types of NPs, this thesis will further reveal the mechanism of the interrelations between host LC molecules and NP, considering the role of variables such as core composition, size and surface chemistry of NPs (e.g. siloxane shell, aliphatic ligand vs. liquid crystalline ligand) in achieving stable LC composites with desired optical and electro-optical properties.

The goal of this research is to contribute to the development of MARS spectral CT and to demonstrate the feasibility of molecular imaging using the technology. MARS is a newly developed micro CT scanner, incorporating the latest spectroscopic Medipix photon counting detector. I show that the scanner can identify both drug markers and stenosis of atherosclerosis labelled with non-toxic nanoparticles. I also show that spectral computed tomography using Medipix x-ray detectors can give quantitative measurements of concentrations of gold nanoparticles in phantoms, mice and excised atheroma. The characterisation of the Medipix2 assemblies with Si and CdTe x-ray sensors using poly-energetic x-ray sources has been performed. I measure the inhomogeneities within the sensors; individual pixel sensitivity response; and their saturation effects at higher photon fluxes. The effects of charge sharing on the performance of Medipix2 have been assessed, showing that it compromises energy resolution much more than spatial resolution. I have commissioned several MARS scanners incorporating several different Medipix2 and Medipix3 cameras. After the characterization of x-ray detectors and the geometrical assessment of MARS-CT, spectral CT data has been acquired, using x-ray energies that are appropriate for human imaging. The outcome shows that MARS scanner has the ability to discriminate among low atomic number materials, and from various concentrations of heavy atoms. This new imaging modality, used with functionalized gold nanoparticles, gives a new tool to assess plaque vulnerability. I demonstrated this by using gold nanoparticles, attached to antibodies, which targeted to thrombotic events in excised plaque. Likewise, the imaging modality can be used to track drugs labelled with any heavy atoms to assess how much drug gets into a target organ. Thus the methodology could be used to accelerate development of new drug treatments for cancers and inflammatory diseases.

Abstract: A brief overview of this PhD thesis, The emergence of nanotechnology has stimulated both fundamental and industrially relevant studies of the catalytic activity of noble metal nanoparticles. Palladium, ruthenium and gold are well known catalysts when used in nanoparticle- based systems. This body of work endeavoured to investigate the catalytic activity of these noble metal nanoparticles through three studies as a briefly overviewed below. Study 1: Palladium is a well-known catalyst, even in bulk phases, but its high cost had driven industry towards its use in nanoparticle- based systems well before nanotechnology had attracted the attention of the media. Palladium nanoparticles often show remarkable catalytic activity and selectivity, particularly for the hydrogenation of some unsaturated hydrocarbons, such as alkenes, alkynes and unsaturated carbonyl compounds. The nature of supports can affect the catalytic activity and selectivity of metal-support interaction. Natural polymeric supports, such as wool, can be suitable for new generation of composite materials incorporating nanosized metal nanoparticles and have the added advantage of being “environmentally friendly”. Catalytic hydrogenation of cyclohexene to cyclohexane by palladium nanoparticles immobilized on wool was demonstrated by using a Parr high pressure hydrogenation set-up. The efficiency of the process was explored over loading rates from 1.6% to 2.6% of palladium nanoparticles (by weight) with a variety of particle sizes. Optimization of the reaction conditions including, stirring rate, amounts of reactants, gas pressure and target temperature, led to series of catalytic activity tests carried out for 5 or 24 hours (each) at 400psi H2 and 40 oC using a stirring rate 750 rpm. Product mixtures were analysed using gas chromatography (GC-FID) to determine conversions. Samples S1 and S2 proved to be the most active catalysts because the average Pd particle size was around ~5 nm and the particles were more accessible for the reactant (i.e., Pd particles were on the surface of wool). However, under the catalytic testing conditions studied, wool (Pd/wool) did not show advantages over commercially used palladium nanoparticles on activated carbon (Pd/C). Study 2: Ruthenium fabricated as noble metal nanoparticles can be catalytically active for hydrogenation of organic compounds. However, a challenging issue for researchers is that Ru nanocatalysts can be spontaneously deactivated due to effects, such as sintering or leaching of active components, oxidation of noble metal nanoparticles, inactive metal or metal oxide deposition and impurities in solvents and reagents. Calcination of noble metal nanoparticles is one option for reactivation of Ru nanoparticles immobilized on SiO2 (Ru/SiO2) utilized as nanocatalysts in chemical reactions. In fact, the catalytic activity of noble metal nanoparticles is known to be proportional to the active part of the surface area. The effects of calcinations on catalytic activity of “shape- specific” 0.1 wt% Ru/SiO2 for hydrogenation of cyclohexene to cyclohexane were investigated. Optimization of calcinations by varying temperature and time proved to be effective on the activity of nanocatalysts retaining the Ru nanocatalysts shapes for the hydrogenation of cyclohexene. Product mixtures were analysed using gas chromatography (GC-FID) to determine conversions. The Ru catalysts showed the highest activity (100%) when they were activated by calcination following protocol No.1 in a furnace under the mildest reductive conditions studied (temperature = 200 oC for 1 hour, which was the shortest calcination time). HRTEM study showed only minor deformation of the Ru nanoparticles and minimal aggregation for this type of activation. Study 3: Supported gold nanoparticles have excited much interest owing to their unusual and somewhat unexpected catalytic activity particularly with the selective oxidation of organic compounds. Gold nanoparticles immobilized on Norit activated carbon (Au101/C) via colloidal deposition gave high selectivity of benzyl alcohol oxidation. The presence of a base (K2CO3) increased the catalytic activity of gold nanocatalysts (which was negligible in the absence of base) through dehydrogenation of the alcohol via deprotonation of a primary OH groups, and helped overcome the rate-limitation step of the oxidation process. The interaction between the gold species and the support was investigated by measuring change in catalytic activity with different activation methods (i.e., washing with a solvent at elevated temperature, and/or followed by calcinations). A mixture of benzyl alcohol as a reactant, methanol as a solvent, K2CO3 as a base and oxygen gas was studied by the activated gold nanocatalysts using a mini reactor set-up. The efficiency of the process was explored by varying the amounts of benzyl alcohol and the base, target temperature, metal loading of the gold catalysts rate and the solvent, between 3 and 24 hours at 73 psi O2 and a stirring rate (750 rpm). The samples of the reaction mixture were centrifuged and analysed by highperformance liquid chromatography (HPLC) to determine conversions. The effect of size on the catalytic activity was studied for different types of gold particles (Au101, Aunaked and Aucitrate) and clusters (Au8 and Au9) immobilized on powder Norit activated carbon. The highest activity of benzyl alcohol oxidation was observed for activated 1.0 wt% Au101/C catalysts (washed with toluene and followed by calcination under vacuum at 100 oC for 3 h) for ~3.5 nm gold particles. Additionally, the support effect was studied for gold particles immobilized on different types of carbons, such as Norit activated carbon (powder, granular and powdered) and mesoporous carbons (CMK-3, CMK-8 and NCCR-41), granular modified carbon (–SH and –SO3H groups) and Vulcan carbon. The highest activity was observed by activated 1.0 wt% Au101/C8 catalysts (washed with toluene and followed by calcination under vacuum at 100 oC for 3 h). Activated 1% Au101/C41 (washed with toluene followed by calcination under vacuum at 100 oC for 3 hours) with 2.6 ± 0.1 nm gold particle size showed the highest selectivity towards methyl benzoate as a main product (S%: 88%) after 3 hours reaction time. However, activated 1% Au101/C (calcination in O2 -H2 at 100 oC for 3 hours) with 6.6 ± 0.3 nm gold particle size exhibited the highest selectivity towards benzoic acid as a main product (S: 86%) after 24 hours reaction time.Therefore, particle size and type of carbon support can be considered as playing crucial roles in defining the catalytic activity of gold nanocatalysts which were used for benzyl alcohol oxidation.

The work presented in this thesis explores the optical properties of hierarchical structures composed of nanoscale building blocks ranging from metals to semiconductors and composites, organized through bottom-up design methods. 1) By following the dynamic generation of hot-spots in self-assembled chains of gold nanorods (NRs), we have established a direct correlation between ensemble-averaged surface-enhanced Raman scattering (SERS) and extinction properties of these nanoscale chains. Experimental results were supported by comprehensive finite-difference time-domain simulations (FDTD). The relationship established between the structure of nanorod ensembles and their optical properties provides a basis for producing dynamic, solution-based, plasmonic platforms for applications ranging from sensing to nanoelectronics. 2) We report theoretical and experimental analyses of the optical properties of side-by-side assembled gold NRs. Comprehensive FDTD simulations showed a blue shift of the surface plasmon resonance in the side-by-side assembled NR structures and a reduction of electric field intensity as the number of NRs per stack increased. These results were experimentally verified via extinction measurements and ensemble-averaged SERS spectroscopy. The experimental results and electrodynamic simulations were found to be in agreement. 3) The efficacy of hollow core photonic crystal fibers (HCPCF) as a platform for SERS spectroscopy was demonstrated. SERS measurements carried out using this platform showed the capability to monitor minute amounts of ligands on the surface of gold nanoparticles and SERS signals from HCPCF exhibited a 10-fold enhancement. Using the exchange of cetyltrimethylammonium bromide with α-methoxy-ω mercaptopolyethylene glycol on the surface of gold nanorods as an exemplary system, we showed the feasibility of using HCPCF SERS to monitor the change in surface chemistry of NRs. 4) Facile, solution-phase formation of ordered, lamellar quantum dot (QD) arrays exhibiting structural integrity and temporal stability, without the need for chemical crosslinking, was achieved. While micrometers in diameter, they are typically only two to three QD layers thick. These structures are capable of carrying a cargo of water-soluble ions, molecules, metal nanoparticles, or biomolecules. The photoluminescence of the host CdSe QDs were enhanced by the encapsulation of gold nanoparticles within the lamellae, demonstrating the ability to modulate their properties through the cargo they carry. 5) This chapter explores a bottom-up method to produce a metamaterial designed to function as an optical cloak in the visible range. A composite material consisting of an array of silver nanowires (NWs) in a dielectric host has been produced based on the theory of a non-magnetic optical cloak. The required radial array of silver NWs was achieved by electroless deposition of the metal into the channels of a porous alumina structure grown perpendicularly from the curved surface of a micrometer scale aluminum wire. The functionality of the cloak was demonstrated by partial cloaking in the visible range (540 nm).

The work presented in this thesis explores the optical properties of hierarchical structures composed of nanoscale building blocks ranging from metals to semiconductors and composites, organized through bottom-up design methods. 1) By following the dynamic generation of hot-spots in self-assembled chains of gold nanorods (NRs), we have established a direct correlation between ensemble-averaged surface-enhanced Raman scattering (SERS) and extinction properties of these nanoscale chains. Experimental results were supported by comprehensive finite-difference time-domain simulations (FDTD). The relationship established between the structure of nanorod ensembles and their optical properties provides a basis for producing dynamic, solution-based, plasmonic platforms for applications ranging from sensing to nanoelectronics. 2) We report theoretical and experimental analyses of the optical properties of side-by-side assembled gold NRs. Comprehensive FDTD simulations showed a blue shift of the surface plasmon resonance in the side-by-side assembled NR structures and a reduction of electric field intensity as the number of NRs per stack increased. These results were experimentally verified via extinction measurements and ensemble-averaged SERS spectroscopy. The experimental results and electrodynamic simulations were found to be in agreement. 3) The efficacy of hollow core photonic crystal fibers (HCPCF) as a platform for SERS spectroscopy was demonstrated. SERS measurements carried out using this platform showed the capability to monitor minute amounts of ligands on the surface of gold nanoparticles and SERS signals from HCPCF exhibited a 10-fold enhancement. Using the exchange of cetyltrimethylammonium bromide with α-methoxy-ω mercaptopolyethylene glycol on the surface of gold nanorods as an exemplary system, we showed the feasibility of using HCPCF SERS to monitor the change in surface chemistry of NRs. 4) Facile, solution-phase formation of ordered, lamellar quantum dot (QD) arrays exhibiting structural integrity and temporal stability, without the need for chemical crosslinking, was achieved. While micrometers in diameter, they are typically only two to three QD layers thick. These structures are capable of carrying a cargo of water-soluble ions, molecules, metal nanoparticles, or biomolecules. The photoluminescence of the host CdSe QDs were enhanced by the encapsulation of gold nanoparticles within the lamellae, demonstrating the ability to modulate their properties through the cargo they carry. 5) This chapter explores a bottom-up method to produce a metamaterial designed to function as an optical cloak in the visible range. A composite material consisting of an array of silver nanowires (NWs) in a dielectric host has been produced based on the theory of a non-magnetic optical cloak. The required radial array of silver NWs was achieved by electroless deposition of the metal into the channels of a porous alumina structure grown perpendicularly from the curved surface of a micrometer scale aluminum wire. The functionality of the cloak was demonstrated by partial cloaking in the visible range (540 nm).

This research focuses on the microwave properties of nanoparticles for use as contrast and hyperthermia agents. Currently, visible light is used for irradiation of nanoparticles as hyperthermia agents. Additionally, visible/Near-infrared light is used for photoacoustic tomography (PAT) imaging. Compared to optical wavelengths, frequencies in microwave range transmit through tissue with high penetration depth . Thus, deep cancerous cells and malignant tissue may be treated and imaged. These nanoparticles could enable the use of a hybrid microwave/acoustic technique known as thermoacoustic tomography. Here, quantitative measurements of the heat generation in super paramagnetic iron oxide nanoparticle (SPIONs), gold nanoparticles (AuNPs), and gold nanoclusters (AuNCs) induced by microwave energy at 3 GHz, are presented and compared. Based on our experiments, SPIONs are the most efficient nanoparticles for microwave heating. Very high concentrations of SPIONs are able to convert microwave energy into heat about 22° C more than DI-water. AuNPs, which support plasmon resonances, do not provide heat under microwave irradiation as predicted by our computational analysis based on Mie Theory. AuNCs are a new form of ultra-small (<2.5 nm) AuNPs which do not support plasmonic resonances and have supra-molecular properties such as sub-conduction band transitions. Interestingly, AuNCs have the potential to absorb microwave energy and may provide an alternative to SPIONs. These nanoparticles had not yet been studied before in this frequency region. In addition, the absorption coefficient of nanoparticles were calculated using complex permittivity data from a dip probe kit and a Vector Network Analyzer (VNA) in a broad band range from 500 MHZ to 10 GHz. This method allows identification of best frequency region with highest penetration depth. In the last step, the nanoparticles with different concentrations were tested as exogenous contrast agents in a Thermoacoustic Tomography (TAT) system. TAT utilizes the penetration depth of microwave energy while producing high resolution images through acoustic waves. The addition of an exogenous contrast agent improves image quality by more effectively converting microwave energy to heat. The experiment reveals that the time resolved thermoacoustic signal (TA) from SPIONs is stronger than AuNPs and AuNCs and thus, the image contrast produced by SPIONs is stronger than the two other aforementioned nanoparticles.

This dissertation presents the design of organic/inorganic hybrid 2D and 3D nanostructured arrays via controlled assembly of nanoscale building blocks. Two representative nanoscale building blocks such as carbon nanotubes (one-dimension) and metal nanoparticles (zero-dimension) are the core materials for the study of solution-based assembly of nanostructured arrays. The electrical, mechanical, and optical properties of the assembled nanostructure arrays have been investigated for future device applications. We successfully demonstrated the prospective use of assembled nanostructure arrays for electronic and sensing applications by designing flexible carbon nanotube nanomembranes as mechanical sensors, highly-oriented carbon nanotubes arrays for thin-film transistors, and gold nanoparticle arrays for SERS chemical sensors. In first section, we fabricated highly ordered carbon nanotube (CNT) arrays by tilted drop-casting or dip-coating of CNT solution on silicon substrates functionalized with micropatterned self-assembled monolayers. We further exploited the electronic performance of thin-film transistors based on highly-oriented, densely packed CNT micropatterns and showed that the carrier mobility is largely improved compared to randomly oriented CNTs. The prospective use of Raman-active CNTs for potential mechanical sensors has been investigated by studying the mechano-optical properties of flexible carbon nanotube nanomembranes, which contain freely-suspended carbon nanotube array encapsulated into ultrathin (<50 nm) layer-by-layer (LbL) polymer multilayers. In second section, we fabricated 3D nano-canal arrays of porous alumina membranes decorated with gold nanoparticles for prospective SERS sensors. We showed extraordinary SERS enhancement and suggested that the high performance is associated with the combined effects of Raman-active hot spots of nanoparticle aggregates and the optical waveguide properties of nano-canals. We demonstrated the ability of this SERS substrate for trace level sensing of nitroaromatic explosives by detecting down to 100 zeptogram (~330 molecules) of DNT.

In nature, organisms have long been able to create elaborate mineral structures at ambient temperatures. From a materials science and engineering perspective, favorable properties emerge when the synthesis process can be controlled at finer levels. New strategies in materials chemistry synthesis has been inspired by biomineralization: biomimetics. In this work, silk fibroin films were used to synthesize gold nanoparticles room temperature by soaking a free standing 15nm silk film in HAuCl4. Particles ranged in size and shape from 5nm spheres to 105nm hexagons. Secondly, a film of ZnO1 peptide (ZnO selectively binding peptide) was successfully formed by drop casting on both silk and polystyrene surfaces. Using a HMT + Zn(NO3)2 system for ZnO wet chemical deposition, rods were formed on the peptide surface. Changing solution concentration and growth time affected the density and size of the nanorods. Spin coating a 3nm peptide film reduced the roughness to <1nm, upon which an array of vertical ZnO rods with controllable density was synthesized.

This work explores two very different structural systems: n-type hydrogenated amorphous silicon (a-Si:H) and gold nanoparticles (AuNPs) suspended in a matrix of organic ligands. For a-Si:H, examination of the gas-phase concentration of dopant (1-6% PH3/SiH4) and argon diluent effects includes the temperature dependent conductivity, low-frequency electronic noise, and Raman spectroscopy to examine structure. It is found that a-Si:H samples grown with high dopant concentration or with argon dilution exhibit an anomalous hopping conduction mechanism with an exponent of p=0.75. An experimental approach is used to determine correlations between conduction parameters, such as the pre-exponential factor and the characteristic temperature, rather than an analysis of existing models to explain the anomalous conduction. From these results, the anomalous conduction is a result of a change in the shape of the density of states and not a shift of the Fermi level with dopant. Additionally, it is found that argon dilution increases the carrier mobility, reduces the doping efficiency, and causes a degradation of the short-range order. With AuNPs, a comparison of temperature dependent conductivity and low-frequency noise shows that the temperature coefficient of resistance (TCR) is independent of the length of interparticle distance while the noise magnitude decreases.

Thesis (Ph. D.)--University of Massachusetts Amherst, 2009. / Includes bibliographical references (p. 143-163). Print copy also available.