Hydrogen-related defects in single-crystal ZnO and rutile TiO2 are investigated by means of infrared absorption, Raman scattering, photoluminescence and photoconductivity. Four different defect centers in ZnO are considered: bond-centered hydrogen (HBC ), hydrogen bound within the oxygen vacancy (HO), hydrogen molecules, and a defect, which gives rise to a local vibrational mode at 3326 cm−1 . The measurements identify HBC as a shallow donor with an ionization energy of 53 meV. The internal 1s → 2p transition of HBC is detected at 330 cm−1 in the Raman scattering and photoconductivity spectra. The decay of an exciton bound to HBC results in the photoluminescence line at 3360.1 ± 0.2 meV. The local vibrational mode of the O–H bond for bond-centered hydrogen has a frequency of 3611 cm−1 (H-I) and an effective charge of 0.28±0.03e. It is found that bond-centered hydrogen is unstable against annealing at 190 °C due to diffusion and trapping by other defects. The dominant sink is the hydrogen molecule. It is demonstrated that the well-known I4 photoluminescence line at 3362.8 meV is due to the recombination of excitons bound to the HO donor. The ionization energy of the HO donor is determined to be 47 meV. The 1s → 2pz (2pxy) electronic transition of HO is detected at 265 cm−1 in photoconductivity spectra. The formation of HO occurs via trapping of HBC at vacancies left by out-diffusing oxygen. It is shown that sub-band gap illumination leads to an intensity reduction of the O–H local vibrational mode at 3326 cm−1 and the appearance of a previously unreported infrared absorption line at 3358 cm−1. The signals are identified as stretch modes of an O–H bond associated with the same defect in different charge states. The measurements indicate that this defect has a deep level in the band gap of ZnO at roughly Ec − 1.7 eV. Additionally, results on the thermal stability, uniaxial stress response, and temperature dependence of the transition rates between the two charge states of this defect are presented. Interstitial hydrogen in rutile TiO2 is studied by infrared absorption. It is shown that the defect is a shallow donor with an ionization energy of 10 meV. The absorption lines at about 3290 cm−1 consists of local vibrational modes due to the neutral and the positive charge states of the donor with relative intensities depending on the measurement conditions. In the neutral charge state, the defect reveals two modes at 3288.3 and 3292 cm−1 (10 K), whereas the positive charge state has a vibrational mode at 3287.4 cm−1. An unknown hydrogen complex was found to contribute to the 3288 cm−1 feature.

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Indiana University-Purdue University Indianapolis (IUPUI) / INTRODUCTION: New sealers have been placed on the market to improve the property of a hermetic seal within the root canal and decrease the gap between the gutta-percha and dentin wall. Differences in the adhesive properties of endodontic sealers may be expected because their interaction with either dentin or gutta-percha may vary with their chemical composition. No specific interaction either with dentin or gutta-percha is expected from the setting reaction of calcium hydroxide based sealers and the epoxy-based sealers. The setting reaction of the zinc oxide-eugenol mixtures is a chelation reaction occurring with the zinc ion of the zinc oxide. Development and maintenance of the seal are essential to optimize the long-term success rate of root canal treatment. An ideal endodontic sealer should, in part, adhere firmly both to dentin and gutta-percha. PURPOSE: The purpose of this study is to evaluate the sealing properties of EndoSequence BC sealer TM ,a bioceramic sealer, and Roth’s sealer using gutta-percha with warm vertical condensation and using the single cone technique with the EndoSequence BC sealer only. The goal is to see if there is a significant difference in microleakage between teeth sealed with the bioceramic sealer and teeth sealed with Roth’s sealer. MATERIALS & METHODS: Eighty-five single-rooted maxillary anterior teeth were used for this study. Endodontic cleaning and shaping of each root canal system was accomplished using K-type hand files and NiTi Rotary files. Group A consisted of twenty-seven anterior teeth, which were obturated using EndoSequence BC sealer and gutta-percha with System B and Obtura. Another twenty-seven anterior teeth, Group B, was obturated using Roth’s sealer and gutta-percha with System B and Obtura. A final group, Group C with 27 teeth was obturated using the single cone technique by means of a single gutta-percha point with Endosequence BC sealer. Two teeth were used as a positive control group, and two other teeth as a negative control group. A microbial leakage apparatus was constructed using a similar two-chamber method described by Torabinejad et al. E. faecalis ATCC 29212 was the test bacteria which was used in this study to determine microleakage The outcome of interest (bacterial turbidity) and time-to-leakage (in days), will be determined for each of the samples. Survival analysis will be used to compare the two groups, with a Kaplan-Meier plot to visualize the results and a nonparametric log-rank test for the group comparison RESULTS: No microleakage was observed in the negative control or group B. Microleakage was observed in all the positive control. Group A and C had a significantly higher proportion of samples with microleakage than group B (p<0.0001), but group A and C were not significantly different from each other (p=0.50). Time to microleakage was also significantly lower in group A and C than group B (p<0.0001), but group A and C were not significantly different from each other (p=0.37). CONCLUSION: In conclusion, using E. faecalis as our test bacteria, the microleakage of canals obturated with gutta percha and Roth's sealer was significantly less than canals obturated with gutta percha and EndoSequence BC sealer.

This dissertation describes advances in the microfabrication of thin layer chromatography (TLC) plates. These plates are prepared by the patterning of carbon nanotube (CNT) forests on substrates, followed by their infiltration with an inorganic material. This document is divided into ten sections or chapters. Chapter 1 reviews the basics of conventional TLC technology. This technology has not changed substantially in decades. This chapter also mentions some of the downsides of the conventional approach, which include unwanted interactions of the binder in the plates with the analytes, relatively slow development times, and only moderately high efficiencies. Chapter 2 focuses primarily on the tuning of the iron catalyst used to grow the CNTs, which directly influences the diameters of the CNTs grown that are produced. Chapter 3 focuses on the atomic layer deposition (ALD) of SiO2 from a silicon precursor and ozone onto carbon-nanotubes to obtain an aluminum free stationary phase. This approach allowed us to overcome the tailing issues associated with the earlier plates prepared in our laboratory. Chapter 4 is a study of the hydroxylation state of the silica in our TLC plates. A linear correlation was obtained between the SiOH+/Si+ time-of-flight secondary ion mass spectrometry (ToF-SIMS) peak ratio and the isolated silanol peak position at ca. 3740 cm-1 in the diffuse reflectance infrared spectroscopy (DRIFT) spectra. We also compared the hydroxylation efficiencies on our plates of ammonium hydroxide and HF. Chapter 5 reports a series of improvements in TLC plate preparation. The first is the low-pressure chemical vapor deposition (LPCVD) of silicon nitride onto CNTs, which can be used to make very robust TLC plates that have the necessary SiO2 surfaces. These TLC plates are the best we have prepared to date. We also describe here the ALD deposition of ZnO into these devices, which can make them fluorescent. Chapters 6 – 10 consist of contributions to Surface Science Spectra (SSS) of ToF-SIMS spectra of the materials used in our microfabrication process. SSS is a peer-reviewed database that has been useful to many in the surface community. The ToF-SIMS spectra archived include those of (i) Si/SiO2, (ii) Si/SiO2/Al2O3, (iii) Si/SiO2/Al2O3/Fe, (iv) Si/SiO2/Fe (annealed at 750 °C in H2), and (v) Si/SiO2/Al2O3/Fe(annealed)/CNTs. Both positive and negative ion spectra have been submitted. In summary, the present work is a description of advances in the development, thorough characterization, optimization, and application development of microfabricated thin layer chromatography plates that are superior to their commercial counterparts.

Основной целью данной работы являлось исследование условий, необходимых для роста наноструктур на основе водного коллоидного раствора с наночастицами, созданными с помощью лазерной абляции мишени металлического цинка. Исследования проводились при помощи различных методик, включая СЭМ, ПЭМ, РФЭС и оптическое поглощение, позволяющих исследовать форму и состав полученных наночастиц. В первой части работы содержится обзор литературных источников, посвященный механизму формирования наночастиц, принципиальной схеме синтеза наночастиц методом лазерной абляции в жидкости и основным характеристикам наночастиц оксида цинка. Вторая часть работы включает в себя цели и задачи, поставленные в данной работе. В третьей части описаны методики получения и исследования наночастиц. Четвертая часть посвящена данным, полученным в ходе синтеза, описанию характеристик и свойств наночастиц, а также сформулированным выводам. В результате проведения исследования показано, что импульсная лазерная абляция цинка в воде позволяет создавать наночастицы оксида цинка способные к ориентированному росту. / The main goal of this work was to investigate the conditions necessary for the growth of nanostructures in water based colloid produced by laser ablation of metallic zinc. The studies were carried out using various techniques, including SEM, TEM, XPS, and optical absorption, which made it possible to study the shape and composition of the nanoparticles. The first part of the work contains a review of literature sources devoted to the mechanism of nanoparticle formation, the principle scheme of the nanoparticle synthesis by laser ablation in liquid, and the main characteristics of zinc oxide nanoparticles. The second part of the work includes the goals and objectives set in this work. The third part describes methods for obtaining and studying nanoparticles. The fourth part is devoted to the obtained data, the characteristics and properties of nanoparticles, and the conclusions. It was shown that pulsed laser ablation of zinc in water allows to create zinc oxide nanoparticles capable of oriented growth.

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Despite the many attractive features of carbon fiber reinforced polymers (FRPs) composites, they are prone to failure due to delamination. The ability to tailor the fiber/matrix interface FRPs is crucial to the development of composite materials with enhanced structural performance. In this dissertation, ZnO nanowires (NWs) were grown on the surface of carbon fibers utilizing low temperature hydrothermal synthesis technique prior to the hybrid composite fabrication. The scanning electron microscopy revealed that the ZnO nanowires were grown uniformly on the surface of the carbon fabric. The surface grown ZnO NWs functionally-graded the composite material properties and ensured effective load transfer across the interface. To assess the influence of the ZnO NWs growth, reference samples were also prepared by exposing the carbon fabric to the hydrothermal conditions. The damping properties of the hybrid ZnO NWs-CFRP composite were examined using the dynamic mechanical analysis (DMA) technique. The results showed enhanced energy dissipation within the hybrid composite. Quasi-static tensile testing revealed that the in-plane and out-of-plane strengths and moduli of the hybrid FRP composite were also boosted. The interlaminar shear strength (ILSS) measurements suggested the improvement in the mechanical properties of the composite to the enhanced adhesion between the ZnO nanowires and the other constituents (carbon fiber and epoxy). It was necessary thus, to utilize the molecular dynamics simulations (MD) to investigate the adhesion within the CFRP structure upon growing the ZnO nanowires on the surface of the carbon fibers. Molecular models of the carbon fibers, the epoxy matrix and the ZnO nanowires were built. The resulting molecular structures were minimized and placed within a simulation box with periodic boundary conditions. The MD simulations were performed using the force field COMPASS to account for the empirical energy interactions between the different toms in the simulation box. Proper statistical thermodynamics were employed to relate the dynamics of the molecular model to the macroscale thermodynamic states (pressure, temperature and volume). Per the computed potential energies of the different components of the composite, it was found that the polar surfaces in the ZnO structures facilitates good adhesion properties in the graphite-epoxy composite. Besides the attractive mechanical properties of the ZnO nanowires, their piezoelectric and semiconductor properties were sought to design an energy harvesting device. To ensure sufficient charges collection from the mechanically stressed individual ZnO nanowires, a copper layer was sputtered on top of the ZnO nanowires which introduced also a Schottky effect. The mechanical excitation was provided by exposing the device to different vibration environment. The output voltage and currents were measured at the conditions (in terms of frequency and resistive load). It was demonstrated that the electrical output could be enhanced by stacking up similar devices in series or in parallel. Finally, in an attempt to exploit the reversibility of the electromechanical coupling of the energy harvesting device, the constitutive properties of the hybrid ZnO nanowires-CFRP composite were estimated using the Mori-Tanaka approach. This approach was validated by a finite element model (FEM). The FEM simulations were performed on a representative volume element (RVE) to reduce the computational time. The results demonstrated that the mechanical properties of the hybrid ZnO NWs-CFRP composite were better than those for the baseline CFRP composite with identical carbon fiber volume fraction (but with no ZnO NWs) which confirmed the experimental findings. Furthermore, the electro-elastic properties of the hybrid composite were determined by applying proper boundary conditions to the FE RVE. The work outlined in this dissertation will enable significant advancement in the next generation of hybrid composites with improved structural and energy harvesting multifunctionalties. / Ph. D.