No description available.

No description available.

Repairing injured nervous systems requires the ability to regenerate axons and to guide growing axons to their targets. To achieve guidance, mechanistic studies in physiological axon guidance in developing neurons will be critical. It is known that the growth cone, the structure at the leading edge of developing axons, responds to chemical and mechanical cues in the environment to steer the axon to its target, and chemotropic cues have been well characterized. However, the mechanotransduction pathways involved in axon guidance are currently not well understood. Photoacoustics offers a means for mechanical stimulation of neurons that can be used to study axon guidance by mechanotransduction. Compared to other methods, photoacoustics offers a non-genetic, extremely high spatial precision method for neuron stimulation that works by converting pulsed light energy into ultrasound waves by light absorption and subsequent thermal expansion and contraction of the photoacoustic material. In this thesis, photoacoustic stimulation of neuronal growth cones was used to study axon guidance mechanisms. First, a photoacoustic device that was previously developed in this lab was fabricated by applying a photoacoustic composite material coating to the tip of an optical fiber. This device was used for targeting the growth cones of Xenopus laevis primary embryonic neurons in vitro, and subsequent growth patterns were analyzed using optical microscopy with a custom-built quantitative model for measuring growth rates and directional changes. Calcium imaging by Fluo-4 fluorescent dye was used to show successful activation of mechanotransduction pathways. This thesis offers the first evidence that photoacoustic stimulation of growth cones is possible and sets up future research to explore axon guidance by mechanotransduction using photoacoustic stimulation.

The application of functional thin films encompasses a wide range of industries and technologies, where these films are applied to enhance the performance, durability, and functionality of various materials and devices. Specifically, polymer thin films play an important role for their molecular architecture and composition. This work aims to use poly(glycidyl methacrylate)(PGMA) polymer as a backbone and modify the PGMA with phenolic derivatives to perform the phenol-assisted electrodeposition. This work includes the selection of phenolic derivatives, the process of modification, the method of purification, the study of how to tune film thickness, and broadening this method to other polymers. / 2026-05-23T00:00:00Z

Wide bandgap (WBG) semiconductors (Eg >2.0 eV) in two-dimensional (2D) form have demonstrated great potential in 2D electronics, optoelectronics, and power industries. However, as an essential group of WBG semiconductors, 2D transition metal oxides (TMOs) remain largely understudied in terms of physical properties and applications in 2D electronic devices due to the lack of sufficiently large 2D crystals. Here, we accomplish the synthesis of WBG 2D nickel oxide (NiO) (Eg > 2.7 eV) thermally converted from 2D nickel hydroxide (Ni(OH)2) with the largest ever reported lateral domain size (>20 µm). Besides, the process is studied via various X-ray techniques and provides significant insights on the morphology, structure and electronic band structure variation. Moreover, temperature associated defects are monitored by in-situ X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) and low energy inverse photoemission spectroscopy (LEIPS) are demonstrated to characterize band structure of materials, to establish a relation between structural defects and electronic properties.

The highly desirable properties of molten salts have generated a renewed interest in using them not only in Molten Salt Reactors (MSR) as fuel carriers, but in concentrated solar power, thermal storage systems, hydrogen production, oil refineries and as heat transfer fluids. LiF-NaF-KF (46.5-11.5-42 mol% - ‘FLiNaK’) and NaF-ZrF4 (53-47 mol%) are model MSR salts - the former salt is used as a heat transfer coolant and for thermal solar energy storage applications while the latter salt has been used as a fuel carrier and primary coolant. To understand the origin of the salt’s physical and chemical properties, it is important to have knowledge of its atomic structure. This study will discuss the structural data of such molten fluoride salts as a function of temperature using high-energy x-ray scattering and x-ray absorption spectroscopy experiments that were conducted at Beamline 28-ID-1 at NSLS-II, Brookhaven National Lab and Beamline 5-BM-D at Advanced Photon Source, Argonne National Lab. Ab-initio Molecular Dynamics (AIMD) and Neural Network-based Molecular Dynamics (NNMD) simulation results obtained from collaborators will also be compared to experiments through the predicted pair distribution functions and coordination numbers as a function of temperature. These findings contribute to a comprehensive understanding of the complex local structure of the molten salts, providing insights into temperature-dependent preferences and correlations within the molten system.

The demand for clean energy production and storage has inspired research in molten salt-based technologies. Understanding of how molten salts change with respect to temperature is vital to establishing efficient, cost-effective systems. Experimental measurements of physical properties and parallel x-ray studies of material structure can be used together to better understand how the molten salt speciation and behavior changes with temperature. Limited research into such materials means there are knowledge gaps and uncertainty in reported property values with respect to temperature due to difficulties in accurate experimental determination of properties. This is in part due to the stringent environmental requirements necessary due to the reactivity of the materials at elevated temperatures. Additionally, common high temperature techniques are time consuming, limiting the quantity of materials that can be evaluated. Many research efforts attempt to utilize MD modeling to fill these gaps and accelerate this process, however accurate physical measurements are still required to verify the results. This thesis presents the development of glove box compatible techniques that are chosen with the intent of reducing measurement time while still providing accurate results of thermophysical properties as a function of temperature. Studies were performed on two candidate molten salts for one technology of interest, the Molten Salt Reactors (MSRs). The first is FLiNaK, the well-studied eutectic of the LiF-KF-NaF system with the composition of 46.5-11.5-42 mole percent. The second is a lesser studied salt NaF-ZrF4 with a composition of 53-47 mole percent. This salt was chosen as a surrogate for the NaF-ZrF4-UF4 fuel candidate used in the original MSR experiments between 1950 and 1970. Properties measured in this work include viscosity, surface tension and density. Viscosity was measured with a falling ball viscometer adapted to high temperature applications. The intent of this system was to provide viscosity measurements as a function of temperature while minimizing sampling time and sample quantity. The applicable testing conditions were extended beyond the Stokes Flow regime (Reynolds Number < 1) typically used in the classic falling ball viscometer. A high temperature induction sensor was developed to measure the rate of the falling metallic ball, in this case Ti. Additionally, density and surface tension were measured simultaneously as a function of temperature with the maximum bubble pressure method. Combining these property measurements reduces total measurement time by eliminating the need for a second experiment. This method also addresses the effect of surface tension on density measurements that is commented on in published literature for molten salts, including FLiNaK and NaF-ZrF4. Considerations were made on both measurements to address environmental effects that might influence results. Characterization of salt samples before and after measurements were performed to provide context for the accuracy of the measurements with respect to temperature that may arise from these interactions with the environment and the materials used in the experiments.

Fluorine plasma etching is a common process in semiconductor wafer processing. The plasma operations degrade the chamber components that are primarily made of aluminum alloys such as Al-6061. A technology to prolong life of chamber components was sought with the goal of resisting fluorine diffusion. AlN is a well-known diffusion barrier to fluorine in the semiconductor industry. However, there is no available process that can impart a protective AlN layer over large aluminum parts with complex geometries. Moreover, existing processes to deposit AlN on samples with simple geometries require stringent conditions such as high vacuum, toxic reactants, high temperatures or mechanical processing that disturb the component geometry. A process of carrying out surface nitridation of Al-6061 alloy substrates was developed, that allowed for the growth of a dense aluminum nitride coating on samples having complex geometries. The method used nitrogen gas alone as the nitrogen carrier, and not ammonia derivatives unlike conventional AlN synthesis processes. Mg powders in a powder bed placed before the sample along the gas flow path supplied a rapid burst of magnesium vapor to the sample during exothermal nitridation (combustion) of Mg powders. This burst of supersaturated magnesium vapor converted the native protective Al2O3 to non-protective MgO on the sample surface if the extent of magnesium supersaturation, the temperature of the sample, and the residence time of the vapor around the Al-6061 alloy sample were high enough. The process led to uniform coating coverage over the flat sample surfaces as well as over the surfaces of drilled holes in the sample. The coatings were stable when subjected to several 400°C thermal cycles. The advantages of this process are that the process reactants are inexpensive, non-toxic, and is carried out at atmospheric pressure. The AlN coatings were examined using XRD, SEM, EDS, and TEM. The dense and adherent AlN coatings were found to comprise of a two-phase mixture of dendritic AlN interspaced with Al grains, making the coating electrically conductive. Uncoated and AlN coated Al-6061 alloy coupons were exposed to fluorine plasma to assess the effectiveness of the AlN coatings. The results showed that the AlN coated Al-6061 samples resisted fluorine attack significantly better than the uncoated Al-6061 samples. Although fluorine did react with a top layer of the coating forming AlF3, the remainder of the coating and the substrate suffered much less detrimental effects such as cracking or spallation, validating the effectiveness of the AlN coatings.

No description available.

<p>This investigation is primarily concerned with the development of a suitable high-precision sectioning technique to be employed in studies of depth distributions of energetic ions in Mo and V. It consists of two main parts.</p> <p>In the first part, uniform anodic oxide films of controlled thicknesses have been grown on poiycrystalline V, Mo, and W (the latter, primarily for comparison with earlier works on W) in acetic acid-sodium tetraborate solutions containing small quantities of water. These anodic films which show bright characteristic interference colours when formed at >10 volts, are shown to be rapidly soluble in a dilute solution of KOH whereas the underlying metal is attacked at a rate of less than ~100Å per day. The thickness of the anodic films per volt has been established using ellipsometry and conventional weight-loss measurements.</p> <p>Kinetics of anodization have been studied at constant-current and constant-voltage. An analysis of these data shows the composition of the films on Mo and W to be close to Mo0₃ and W0₃ respectively while those on V were intermediate between V₂0₄ and V₂0₅. The density of the films on Mo and the differential field strength, E_d, for films on Mo and W have also been determined.</p> <p>In the second part, a theoretical background consisting of an outline of the theory of Lindhard, Scharff and Schiøtt, has been provided; in the absence of experimental data, this theory is generally used to estimate the depth distribution of ions in amorphous targets. Experimental range profiles have been determined for 5-30 keV Kr⁸⁵ in polycrystalline Mo using the technique developed in the first part and the results obtained show a large discrepancy when compared with Lindhard theory. The extent of disagreement with theory is similar to that obtained by previous workers with targets such as Al or W.</p> <p>Evidence is presented to show that this large discrepancy may be attributted to crystal-lattice effects (i.e. channelling). For example, it is shown that the discrpency is not due to the anodizing-stripping sequence being sensitive to bombardment. Also, it is demonstrated that the Mo used had a pronounced preferred orientation such that the open directiors <100>, <211>, and <111> were normal to the surface.</p> <p>An important part of future work will be to extend techniques such as those described here to the metal Be, for Be is the lightest target material that can be conveniently worked with.</p> / Master of Science (MS)