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We discuss the self-assembled Ni nanoparticles as the etching mask process and produce patterned sapphire substrate in this study. In the Ni nanoparticles formation process, we focus on two major factors which make the Ni films transform into Ni ball, (1)annealing temperature, (2) film thickness. In the experiment, we deposit 2000Ǻ SiO2 on sapphire substrate, and use the E-gun to deposit 100~200Ǻ Ni film. After the Ni film deposition, we use the rapid thermal annealing at 900oC standing for 60sec, and make the Ni film transform into Ni spherical calotte which is resulting from the Ni film cohesive force. In the SiO2 etching process, we use CF4, 20sccm as reactive gas and the Ni calotte as etching mask to form SiO2 nanopillars. Then, we mixed Cl2 and SiCl4 reactive gas, 5sccm and 20sccm, and use SiO2 nanopillars as the etching mask in the dry etching process to form patterned sapphire substrate. We obtain the optimum rapid thermal annealing for self-assembled Ni calotte at 100, 200Ǻ Ni film. We got the patterned sapphire substrate nanopillars at density of 1.59x109cm-2, average height ~64.3nm, average diameter ~106nm, and density of 6.20x108cm-2, average height ~160nm, average diameter ~193nm for 100, and 200Ǻ Ni film process condition, respectively. We use 160nm sapphire nanopillars to increase 18.0-10.3% scattering light for 350~450nm blue light LED application.

Thesis advisor: Krzysztof Kempa / It is well established that molecules can be driven to dissociation via ionizing radiation, and this has various uses in medicine. The drawback is that ionizing radiation has little spectral resolution when applied to the human body. Consequentially, ionizing radiation damages target biological cells and healthy biological cells indiscriminately. If a truly non-invasive and selective dissociation method is desired, it is necessary to consider non-ionizing radiation for additional specificity. The first part of this thesis proposes that a selective dissociation of biomolecules is possible with non-ionizing electromagnetic radiation on the basis of nonlinear driving of molecular resonances. The second part is devoted to a “Trojan horse”-type of strategy. Experimentally, we demonstrate that visible light at moderate power levels damages metastatic cancer cells when they are sensitized with biocompatible polymeric nanoparticles. Efficient photothermal conversion of nanoparticles triggers hyperthermia-induced lysis in cells in a target-selective manner. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Flotation is arguably the most important mineral separation technique. It has been demonstrated that hydrophobic nanoparticles adsorbed onto hydrophilic mineral surfaces can facilitate mineral particles attachment to air bubbles in flotation process. This thesis explores the effects of nanoparticle adhesiveness, size and shape on the performance of nanoparticle flotation collectors. For this, a series of rigid polystyrene, soft shelled polystyrene-poly (n-butyl methacrylate) (PS-PB) and soft lobed polystyrene/poly (n-butyl methacrylate) (PS/PB) Janus nanoparticles were prepared and characterized. Flotation experiments with glass beads, a model for mineral particles, revealed that soft-shelled particles were more effective collectors than were hard polystyrene particles. The small (92 nm) Janus particles were particularly good flotation collectors for glass beads. The pull-off forces required to remove nanoparticles from glass were measured by AFM and the results were compared to the abilities of the nanoparticles to induce the flotation of hydrophilic glass beads. Soft PS-PB particles were strongly adhering and were very effective nanoparticle flotation collectors. By contrast, hard PS particles were weakly adhering and were poor flotation collectors. These observations led to the hypothesis that weakly adhering nanoparticles were dislodged from the glass bead surfaces during flotation. Experimental support for this hypothesis included: (1) the coverage of nanoparticle on glass bead surfaces decreased with increased conditioning time; (2) large nanoparticles aggregates were detected in flotation pulp as well as on bead surfaces; and, (3) dislodged soft-shelled PS-PB particles left polymeric patches, we call footprints, on the glass bead surfaces. Indeed, the presence of the footprints, suggests that a nano-scale stamping process can be used to cover surfaces with hydrophobic polymer footprints. Arguments are made that hydrodynamic forces alone were insufficient to detach the small nanoparticles from the glass bead surfaces in our experiments. Instead, it is proposed that bead-bead collisions during conditioning and flotation caused weakly adhering particles to detach; a process is termed as “nano-scale ball milling”. Furthermore, geometric arguments show that during a bead-bead encounter, larger nanoparticles are more susceptible to removal than small particles which is consistent with the experimental data. Although all experiments were performed with model glass beads and rather simple nanoparticles, this work has for the first time explained why larger polystyrene nanoparticles are ineffective flotation collectors. The work highlights the need to consider nanoparticle/mineral adhesion when designing collectors for real mineral systems. / Dissertation / Doctor of Philosophy (PhD)

Engineering the nanoparticle - protein association offers a new way to form protein crystals as well as new approaches for arrangement of nanoparticles. Central to this control is the nanoparticle surface. By conjugating polymers on the surface with controlled molecular weights many properties of the nanoparticle can be changed including its size, stability in buffers and the association of proteins with its surface. Large molecular weight poly(ethylene glycol) (PEG) coatings allow for weak associations between proteins and nanoparticles. These interactions can lead to changes in how proteins crystallize. In particular, they decrease the time to nucleation and expand the range of conditions over which protein crystals form. Interestingly, when PEG chain lengths are too short then protein association is minimized and these effects are not observed. One important feature of protein crystals nucleated with nanoparticles is that the nanoparticles are incorporated into the crystals. What results are nanoparticles placed at well-defined distances in composite protein-nanoparticle crystals. Crystals on the size scale of 10 - 100 micrometers exhibit optical absorbance, fluorescence and super paramagnetic behavior derivative from the incorporated nanomaterials. The arrangement of nanoparticles into three dimensional arrays also gives rise to new and interesting physical and chemical properties, such as fluorescence enhancement and varied magnetic response. In addition, anisotropic nanomaterials aligned throughout the composite crystal have polarization dependent optical properties.

A novel method of delivering thermal energy efficiently for flow assurance and for improved heavy oil production/transport is described. The method, an improved form of magnetic induction heating, uses superparamagnetic nanoparticles that generate heat locally when exposed to a high frequency magnetic field oscillation, via a process known as Neel relaxation. This concept is currently used in biomedicine to locally heat and ablate cancerous tissues. Dependence of the rate of heat generation by commercially available, single-domain Fe3O4 nanoparticles of ~10 nm size, on the magnetic field strength and frequency was quantified. Experiments were conducted for nanoparticles dispersed in water, in hydrocarbon liquid, and embedded in a thin, solid film dubbed “nanopaint”. For a stationary fluid heat generation increases linearly with loading of nanoparticles. The rate of heat transfer from the nanopaint to a flowing fluid was up to three times greater than the heat transfer rate to a static fluid. Dispersion models indicated that the thermal conductivity of the dispersing fluid did not greatly influence the heat transfer results, whereas differences in size between hydrophilic and hydrophobic nanoparticles did. The model of static fluid in a nanopainted tube verified that the nanoparticle loading in the paint was ~30wt% and the nanopaint thickness was 600 µm. The model of flowing fluid in a nanopainted tube showed that internal mixing in the system, even at laminar flow rates, improved heat transfer to the center of the flowing fluid. A waveguide model verified the feasibility of using steel hydrocarbon transport pipelines as a means to guide electromagnetic energy to target heating locations along the pipeline if the energy is transmitted at frequencies above the cutoff frequency. Heating of nanopaint with external magnetic field application has immediate potential impact on oil and gas sector, because such coating could be applied to inner surfaces of pipelines and production facilities. A nanoparticle dispersion could also be injected into the reservoir zone or gravel pack near the production well, so that a thin, adsorbed layer of nanoparticles is created on pore walls. With localized inductive heating of those surfaces, hydrate formation or wax deposition could be prevented; and heavy oil production/transport could be improved by creating a ‘slippage layer’ on rock pore walls and inner surfaces of transport pipes. / text

An apparatus intended to measure the pressure oscillations generated by nanoparticle suspensions in response to an AC electric field was designed and made operational. Electroacoustic measurements were performed on nanoparticle systems covering a range of particle sizes and zeta-potentials, determined using typical particle characterization techniques. The results of the electroacoustic experiments were mapped to the hydrodynamic size and zeta-potentials of the various nanoparticle systems. It was determined that while the electroacoustic technique can be used successfully to measure the motion of nanoparticles in response to an AC electric field, additional improvements to the electroacoustic apparatus are required to allow for a more rigorous mapping of electroacoustic measurements to particle hydrodynamic size and zeta-potential.

Nanoparticles (nPs) demonstrate significant advantages over other sensor and marker technologies. The most useful optical nanosensor and label platform for biological samples would be non-toxic, hydrophilic, resistant to non-specific protein interactions and degradation over time or under harsh conditions, highly retentive of entrapped components, and easily functionalized for target specificity. The work described here is part of an investigation into the fabrication and application of polyacrylamide, polyacrylamide/silica hybrid, and polystyrene-core silica-shell nPs. Polyacrylamide (PA) nP nitric oxide (NO) sensors were made by co-entrapping 4, 5-diaminofluorescein (DAF-2) and Texas Red dextran in 60 nm PAnPs. Sensors were used to measure NO produced by a diazeniumdiolate NO donor in solution, and have a response time of 30 seconds or less. Entrapped DAF-2 was protected from non-specific interactions with bovine serum albumin (BSA). Sensor response to NO in FBS solutions was reduced compared to buffer, although improvement over free dyes was observed. The sensors were applied to J477A.1 macrophages as well as a HT1080 cell line (HTRiNOS) in preliminary studies for measuring intracellular NO production. Polyacrylamide/silica hybrid nPs were fabricated and nP architecture was evaluated by transmission electron microscopy. Isopycnic centrifugation of nP samples indicates that the hybrid nPs have a density between 1.70 and 1.76 g/cm³. Silica in the hybrid nPs was covalently labeled with Texas Red, suggesting that the hybrid nPs may be used as ratiometric or possibly multiplexed sensors. Hybrid nPs coated with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) exhibit reduced adsorption of TRITC-BSA compared to uncoated hybrid nPs. Hybrid nP pH sensors were prepared and responded reproducibly and reversibly to changes in pH, nominally from pH 6.0 to 8.0. Core-shell nPs for scintillation proximity assay (SPA) were fabricated by entrapping the scintillants p-terphenyl and 4-bis(4-methyl-5-phenyl-2oxyzolyl)benzene in polystyrene, onto which silica shells were subsequently added. Core-shell nPs were found to have a scintillation response similar to that of shell-less polystyrene cores, indicating that the presence of the silica shells does not reduce scintillation efficiency. Preliminary studies using core-shell nPS for biotin-streptavidin binding SPA do not indicate an enhancement in scintillation efficiency, although this may be due to high nP:radiolabeled analyte ratios.

Engineered nanomaterials (ENMs) are increasing becoming incorporated into consumer products to imbue remarkable physical and chemical properties. The increased use of these ENMs leads to a growing need to understand the environmental fate of ENMs after release. Many ENMs, including Ag and Cu ENMs, have the potential to undergo complex physical and chemical transformations which impact their toxicity, solubility and fate in the environment. There is a lack of research characterizing the transformation rate and understanding how these transformations affect interactions with organisms and the ultimate environmental fate. The first objective of this thesis was to understand how transformations of Ag ENMs affect the uptake, distribution and speciation of these materials in plants. Terrestrial (alfalfa, Medicago sativa) and an aquatic (duckweed, Landoltia punctate) plant species were exposed hydroponically to as manufactured (“pristine”) Ag0-NPs and more environmentally relevant (“transformed”) Ag2S NPs. The uptake, spatial distribution and speciation of Ag were analyzed using synchrotron based X-ray Absorption Spectroscopy (XAS) techniques to provide mechanistic insights into the uptake of these ENMs. The reduced solubility and reactivity of Ag2S ENMs was expected to prevent plants from solubilizing these particles and only allow for direct uptake of particles. For the more soluble Ag species, the absorption of Ag+ ions was expected to be primarily the mechanism of Ag uptake. Although the total Ag associated with the plants was similar, the Ag distribution in the roots was dramatically different. The transformed ENMs (Ag2S) appeared to be taken into the plant tissue as sulfidized ENMs. The pristine Ag0 ENMs were found to partially dissolve and incorporate into the plant tissue as both dissolved Ag and Ag0-NPs. The fact that ENMs readily attach onto plant tissue regardless of speciation and solubility suggests that exposure to ENMs may be controlled by factors affecting attachment to root surfaces. However, internalization of Ag appears to be affected by solubility. The second objective was to characterize the impact of transformations of Ag and Cu-based ENMs on the distribution, speciation and fate of these materials in subaquatic sediments and the aquatic plant, E. Densa in a simulated emergent freshwater wetland using large-scale mesocosms. The exposure of pristine (Ag0 and CuO) ENMs and their transformed analogues (Ag2S and CuS) was compared to an ionic control (Cu(NO3)2) to determine if nanoparticulate species of metals were distributed differently than their dissolved counterparts. The metal speciation was determined using XAS to elucidate relative timescales of transformations. The pristine ENMs were expected to rapidly transform into their more stable sulfidized species and the uptake of Ag and Cu were expected to depend on the solubility of the ENMs. Transformations of the pristine ENMs were found to be rapid (weeks) in the surficial sediment, but slower (months) in the aquatic plant tissue. The uptake of ENMs coupled with the slow transformation in the aquatic plant tissue suggests ENMs persist longer than the timescales measured in sediments. This knowledge enables better risk forecasting for ENMs exposed to aquatic organisms and informs toxicity testing to ensure correct forms of ENMs are examined. This thesis provided several novel contributions to the understanding of how transformations of ENMs affect their interactions with plants and their fate in real complex environments. Mechanistic insights into the attachment and uptake of ENMs into plant tissues were identified suggesting two predominant uptake pathways. Relative timescales of ENM transformations in freshwater wetland sediments and plant tissue provided suggests plants can slow transformations and allow labile ENMs to persist longer than assumed.

Third-generation optoelectronics, which utilize nanoscale materials, have received a considerable amount of attention in the chemical sciences and are poised to make a large impact in both fundamental research and real-world application. In order to make a contribution to the field, this thesis describes a route towards highly stable, water-soluble semiconductor nanorods and their incorporation into nanoparticle/polymer composite thin films. To characterize the photoelectrical properties of these multilayers, and to provide a proof-of-concept for a functional optoelectronic device, the films were integrated into an excitonic solar cell. To gain further insight into the physical properties of the thin films, computational modeling of the carrier transport in thiophenes was conducted, and the limits to device performance were described in the context of their charge transport characteristics. Electrostatic layer-by-layer (ELBL) assembly was used for the synthesis of multilayer nanorod/polymer composite films. CdSe nanorods (NRs) were synthesized and made cationic and water-soluble using ligand exchange chemistry. The NRs were partnered with anionic polymers including poly(sodium 4-styrenesulfonate) (PSS) and the two polythiophene-based photoactive polymers, sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate (PTEBS) and poly[3-(potassium-6-hexanoate)thiophene-2,5-diyl] (P3KHT). Multilayer growth, with nanoscale control, is shown through UV-vis spectroscopy, cross-sectional scanning electron microscopy (SEM) and surface analytical techniques including atomic force microscopy (AFM). The formation of an intimate nanorod/conducting polymer bulk heterojunction is confirmed through cross-sectional SEM, transmission electron microscopy (TEM), and scanning Auger analysis. A series of photovoltaic devices was fabricated on ITO electrodes using CdSe NRs in combination with PTEBS or P3KHT. A thorough device analysis showed that performance was limited by carrier transport throughout the films. Computational modeling of the thiophene component in polymer-based third-generation devices was done using density functional theory (DFT) with core potentials added to account for long range dispersion interactions inherent to optoelectronic thin films. Binding energies and orbital splittings in dimers composed of monomers up to six rings were investigated. The combination of experimental and computational studies elucidates some of the underlying mechanisms behind the production of third-generation solar energy.