Porous silicon, a nanostructured material formed by electrochemical etching of a silicon substrate, is an ideal candidate for constructing optical biosensors due to its large internal surface area, straightforward fabrication, and tunable optical properties that can be exploited to form numerous photonic structures. A major challenge for porous silicon biosensors is its reactive surface that is highly susceptible to oxidation and corrosion in an aqueous environment. In DNA sensing applications, porous silicon corrosion can mask the DNA binding signal as the dissolution of porous silicon is accelerated by the negative charges on the phosphate backbone of the DNA molecules. This corrosion process can be mitigated through surface passivation of porous silicon and the use of charge neutral peptide nucleic acid molecules as capturing probes for DNA targets. Complete mitigation can be achieved by additionally introducing Mg2+ ions to shield the negative charges on the DNA targets. Another key challenge facing porous silicon biosensors is the inefficient analyte transport through nanopores, which can be as slow as a few molecules per pore per second for molecules whose size approaches that of the pore opening. An open-ended porous silicon membrane is demonstrated to overcome the mass transport challenge by allowing analytes to flow through the pores in microfluidic-based assays. The flow-through approach for biosensing using porous silicon membranes enables a 6-fold improvement in sensor response time compared to closed-ended, flow-over porous silicon sensors when detecting high molecular weight analytes (e.g., streptavidin). For small analytes, little to no sensor performance improvement is observed as the closed-ended porous silicon films do not suffer significant mass transport challenges with these molecules. Experimental results and finite element method simulations also indicate that the flow-through scheme enables more reasonable response times for the detection of dilute analytes and reduces the volume of solution required for analysis. Overall, the improvement of surface stabilization and analyte transport efficiency in porous silicon photonic structures opens the door to a fast and reliable optical biosensing platform.

This research is focused on developing a new type of gamma-ray scintillator and is motivated by the need for more accurate positron emission tomography (PET) imaging. PET scans are used to display regions of high-metabolic activity within the body and can indicate the presence of tumors, so clear images are essential for accurate diagnoses and treatment options. Scintillation detectors currently used for PET scans typically have a time resolution of hundreds of ps that yields images with poorly defined and blurred boundaries. Conversely, ZnO nanowires have a response time that is an order of magnitude faster with the potential for an analogous improvement to spatial resolution. Moreover, initial experiments show ZnO nanowires are radiation hardened with highly transient lattice defects. To optimize overall scintillator efficiency, the emission can be enhanced through a combination of optical-cavity effects (15x enhancement) and plasmon-exciton coupling (3x enhancement), while the low interaction volume of the nanowires can be addressed by adding a high-Z backing layer to attenuate incoming gamma rays. The ability to decouple, and address separately, emission efficiency and gamma-ray interaction provides a unique materials workbench and establishes ZnO nanowires as a highly promising PET scan scintillator material.

Gallium arsenide and other III-V materials are well known for their excellent optical and electronic properties and have led to the development of high-performance optoelectronics. Several combinations of III-V semiconductors are now being considered as potentially attractive alternatives to silicon for these applications. However, further development requires fundamental understanding of processes that govern light-matter interactions. Specifically, surface strain and ultrafast dynamics are of great interest to the optoelectronic industry. The research of this dissertation represents an initial exploration of the factors influencing nonlinear optical responses on semiconductor surfaces. The results of this research have the potential to inform the field of nonlinear optics about which lattice behaviors are most likely to contribute to static and transient second harmonic generation (SHG). This information allows for future work to focus on the connection between SHG, dipole contributions, and interatomic potentials in semiconductors under different conditions. This research also provides information about whether strain, resonances, and subpicosecond lattice behaviors can be fit with a simple analytical solution. The results of this research reveal that an analytical fit of polarization-resolved SHG is sensitive to interatomic potential and dipole variations in all three dimensions simultaneously.

Corrosion is a major issue in applications involving materials in normal and severe environments, especially when it involves corrosive fluids, high temperatures, and radiation. Left unaddressed, corrosion can lead to catastrophic failures, resulting in economic and environmental liabilities. In nuclear applications, where metals and alloys, such as steel and zirconium, are extensively em- ployed inside and outside of the nuclear reactor, corrosion accelerated by high temperatures, neu- tron radiation, and corrosive atmospheres, corrosion becomes even more concerning. The objec- tives of this research are to study and develop surface modification techniques to protect zirconium cladding by the incorporation of a specific barrier coating, and to understand the issues related to the compatibility of the coatings examined in this work. The final goal of this study is to recommend a coating and process that can be scaled-up for the consideration of manufacturing and economic limits. This dissertation study builds on previous accident tolerant fuel cladding research, but is unique in that advanced corrosion methods are tested and considerations for implementation by industry are practiced and discussed. This work will introduce unique studies involving the materials and methods for accident tolerant fuel cladding research by developing, demonstrating, and consid- ering materials and processes for modifying the surface of zircaloy fuel cladding. This innova- tive research suggests that improvements in the technique to modify the surface of zirconium fuel cladding are likely. Three elements selected for the investigation of their compatibility on zircaloy fuel cladding are aluminum, silicon, and chromium. These materials are also currently being investigated at other labs as alternate alloys and coatings for accident tolerant fuel cladding. This dissertation also investigates the compatibility of these three elements as surface modifiers, by comparing their mi- crostructural and mechanical properties. To test their application for use in corrosive atmospheres, the corrosion behaviors are also compared in steam, water, and boric-acid environments. Various methods of surface modification were attempted in this investigation, including dip coating, diffu- sion bonding, casting, sputtering, and evaporation. The benefits and drawbacks of each method are discussed with respect to manufacturing and economic limits. Characterization techniques utilized in this work include optical microscopy, scanning electron microscopy, energy-dispersive spec- troscopy, X-ray diffraction, nanoindentation, adhesion testing, and atomic force microscopy. The composition, microstructure, hardness, modulus, and coating adhesion were studied to provide en- compassing properties to determine suitable comparisons and to choose an ideal method to scale to industrial applications. The experiments, results, and detailed discussions are presented in the following chapters of this dissertation research.

The chemical vapour transport reactions of some Group III-V semiconductors with hydrogen halides have been studied hy a modified entrainment method. Enthalpies and entropies for the transport reactions in the systems: indium arsenide-hydrogen bromide, indium arsenide-hydrogen chloride and gallium arsenide-hydrogen bromide were calculated. The effect of surface kinetics on the rate of transport of gallium arsenide by hydrogen bromide gas was investigated. Binary diffusion coefficients for hydrogen bromide and hydrogen chloride gases in hydrogen have been obtained by a study of the transport of indium in hydrogen bromide or hydrogen chloride under limiting equilibrium conditions. Using literature results for the temperature dependence of the vapour pressure of zinc, the binary diffusion coefficients of zinc atoms in helium and in argon over the temperature range 850 - 1120 K were determined. A modified entrainment method apparatus was used to monitor the evaporation of zinc in the inert gas.

<p> The progressive advancements in communication and transportation has changed human daily life to a great extent. While important advancements in battery technology has come since its first demonstration, the high energy demands needed to electrify the automotive industry have not yet been met with the current technology. One considerable bottleneck is the cathode energy density, the Li-rich layered oxide compounds xLi₂MnO₃.(1-x)LiMO₂ (M= Ni, Mn, Co) (0.5= Co) (0.5=discharge capacities greater than 280 mAh g^-1 (almost twice the practical capacity of LiCoO₂).</p><p> In this work, neutron diffraction under <i>operando</i> battery cycling is developed to study the lithium and oxygen dynamics of Li-rich compounds that exhibits oxygen activation at high voltage. The measured lattice parameter changes and oxygen position show movement of oxygen and lattice contractions during the high voltage plateau until the end of charge. Lithium migration kinetics for the Li-rich material is observed under operando conditions for the first time to reveal the rate of lithium extraction from the lithium layer and transition metal layer are related to the different charge and discharge characteristics.</p><p> In the second part, a combination of multi-modality surface sensitive tools was applied in an attempt to obtain a complete picture to understand the role of NH4F and Al₂O₃ surface co-modification on Li-rich. The enhanced discharge capacity of the modified material can be primary assigned to three aspects: decreased irreversible oxygen loss, the activation of cathode material was facilitated with pre-activated Mn³⁺ on the surface, and stabilization of the Ni redox pair. These insights will provide guidance for the surface modification in high voltage cathode battery materials of the future.</p><p> In the last part, the idea of Li-rich has transferred to the Na-ion battery cathode. A new O3 - Na_0.78Li_0.18Ni_0.25Mn_0.583O_w is prepared as the cathode material for Na-ion batteries, delivering exceptionally high energy density and superior rate performance. The single-slope voltage profile and ex situ synchrotron X-ray diffraction data demonstrate that no phase transformation happens through a wide range of sodium concentrations (0.8 Na removed). Further optimization could be realized by tuning the combination and ratio of transition metals.</p>

<p> Low groundwater pH is frequently cited as inhibiting the performance of in-situ bioremediation of chlorinated solvents at contaminated sites. A common method of pH control is injection of solutions containing alkalinity, but alternatives for prolonged, passive pH control are needed. This work explores pH-responsive hydrogel coatings on MgO nanoparticles as vehicles for controlled release of alkalinity. Chitosan cross-linked with glutaraldehyde was evaluated as a representative hydrogel coating. The effects of coating thickness and cross-linking on the rate of alkalinity release were experimentally evaluated using batch dissolution experiments. Dissolution rates were found to be up to an order of magnitude slower for coated particles than for uncoated particles. A diffusion model was developed for the dissolution rate of coated particles, and the model was able to account for the dissolution rate as a function of coating thickness over a range of pH.</p>

<p> Mesoporous silicate have widespread potential applications, such as drug delivery, supports for catalysis, selective adsorption and host to guest molecules. Most important in the area of scientific research and industrial applications is their demand due to its extremely high surface areas (> 800<i>m</i>²<i>g</i>^&minus;1) and larger pores with well defined structures. </p><p> Mesoporous silicate (MCM-41) samples were prepared by hydrothermal method under various chemo-physical conditions and various experimental methods such as small angle X-rays scattering (SAXS), Nitrogen adsorption-desorption analysis at 77 K, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were employed to investigate the changes in the structural morphology and subtle lattice parameter changes. With regards to the subtle changes in the structural characteristics of the synthesized mesoporous silicate, we seek to understand the electron density function changes as the synthesis parameter are varied from low molar concentration of ATAB/Si to higher concentration, the system becoming more acidity due to increase in the hydrolysis time of pH regulator as a result of increased production of ethanol and acetic acid and the changes due to extended reaction time. </p><p> This Ph.D. research tries to understand the influence of various parameters like surfactant-Si molar ratio, reaction time, and the hydrolysis of the pH regulator on the orderliness/disorderliness of the lattice order, lattice spacing and electron density function. The stages during synthesis are carefully selected to better understand where the greater influence on the overall structural morphology exist so as to be able to ne tune this parameter for any desired specification and application. </p><p> The SAXS measurement were conducted on a HECUS S3-Micro X-ray system at Rensselaer Polytechnic Institute, Troy, NY. while the data evaluation and visualization were carried in 3DView 4.2 and EasySWAXS software. The electron density functions were generated with a proprietary software called edens. </p><p> In this dissertation, the following observations have been revealed resulting from SAXS measurement. </p><p> 1. As one increases the hydrolysis duration of ethyl acetate, a gradual collapse of the lattice spacing of the mesoporous silcate MCM-41 is observed. We found from SAXS that there is a slight right shift of the spectra toward the higher q-values indicating that we are gradually losing orderliness in the lattice spacing and hexagonal structure of the mesoporous silica. Also, the intensity of the peak of second and third peaks are diminutive when compared to sample with shorter hydrolysis time. </p><p> 2. A comparison of the SAXS spectra for the different molar concentration sample reveals that the 0:5M samples shows a deteriorating structural characteristics as compared to the 0:25 and 0:75M samples respectively and a clear decrease in the (100) reflection planes. Also noticed is the slight rightward shift in the overall spectrum prole. This observation suggest that further analysis is needed so as to better understand the result. </p><p> 3. We establish that during MCM-41 synthesis, longer reaction time is needed to produce quality sample with well defined structurally characteristic for its intended application because according to spectrum for the sample with a longer reaction time (aging), a shift towards the lower q-values indicates that a sample with a larger lattice parameter and wall thickness but the intensities of its peak are diminishing when compared to the other of relatively shorter reaction time. </p><p> Other complementary techniques were used to corroborated the result obtained from SAXS. Nitrogen adsorption-desorption analysis at 77K was used to generate the isotherms while B.E.T method was used in conjunction with the isotherms to obtained the very important surface area information. SEM provide a visual structural morphology of the samples and FTIR gave the fingerprint detail of the bonds and vibration types between particle present.</p>

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 171-185). / The M13 bacteriophage had been shown to be a highly versatile toolkit for growing and assembling nanomaterials with technological importance. Inspired by the natural biomineralization process, much of the existing literature focused on genetically engineering the M13 viral capsid for interaction with inorganic materials, such as metals and oxides. In this thesis, the utility of the M13 toolkit was extended to the synthesis of organic and carbonaceous materials. Biotemplating of phenolic resins was extensively studied, with a particular focus on colloidal assembly and materials chemistry. Genetically engineered M13 bacteriophage was shown to be particularly apt at controlling the morphology and selfassembly of phenolic resin nanofibers. The properties of these nanomaterials could be simultaneously controlled by introducing additional molecular moieties using simple aqueous, organic chemistry, to enable their application as catalyst scaffolds and carbon dioxide sorbents. / Modification of the phenolic resin nanofibers with organosilicon moieties offered a direct route to nanoporous carbon nanofibers upon carbonization. The properties of these biotemplated carbon nanofibers could be tailored for specific applications by independently controlling morphology and carbon texture. Their practical utility was demonstrated by the rapid adsorption of small molecules with uptake values comparable to some highest values reported for carbon materials. High conductivity nanofibers could also be incorporated into lithium-sulfur batteries as interlayers to significantly improve electrochemical performance. New biotemplating approaches to the synthesis of some other inorganic nanomaterials such as zinc sulfide and noble metal nanomaterials were also demonstrated. Biotemplated zinc sulfide nanofibers were shown to be promising anode material for sodium-ion batteries, with potential for further study. / The facile synthesis of a range of noble metal nanowires opens up potential applications in catalysis and energy storage. / by Geran Zhang. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1985. / Bibliography: leaves 83-85. / by Masayuki Nakada. / M.S.