Browsing by Subject "Gallium"

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    Controlled electrochemical synthesis of giant magnetostrictive iron-gallium alloy thin films and nanowires.
    (2012-04) Reddy, Kotha Sai Madhukar
    Magnetostrictive Galfenol (Fe1-xGax, x = 10% - 40%) alloys have generated tremendous interest in recent times because of their potential as functional materials in various micro- and nano-electromechanical systems (MEMS/NEMS)-based transducers and sensors. Among the giant magnetostrictive alloys, Terfenol-D (Tb1-xDyxFe2) has the largest magnetostriction, but its brittle nature limits its applications. In contrast, the next best magnetostrictive alloy, Galfenol, is highly malleable and ductile while having the tensile strength of Iron. Electrochemistry is an economical route to fabricate 'very thick' films (upto several microns) or high-aspect ratio structures like nanowire arrays. However, the highly electropositive nature of gallium makes it very difficult to electrodeposit from aqueous solutions, similar in behavior to other non-ideal elements like molybdenum, phosphorus, tungsten etc. As a result, Fe1-xGax alloy plating has been severely plagued by non-repeatability in compositions from growth to growth, lack of uniformity in filling of pores when growing nanowires in nanoporous templates, undesired secondary hydrogen evolution reactions etc. In this study, a thorough understanding of the complex interplay between various deposition parameters (pH, overpotential, concentration, hydrodynamic conditions) was achieved, leading to an understanding of the deposition mechanism itself, thus allowing excellent control and ability to tune the alloy compositions. Arrays of nanowires were fabricated with alternating segments of the magnetostrictive alloy Fe1-xGax and Cu in nanoporous anodic aluminum oxide (AAO) templates. A novel rotating disk electrode-template (designed in-house) was used to optimize the nanowire length distributions by controlling the various aspects of electrodeposition like nucleation, kinetics and mass-transfer. Extensive structural characterization was done by X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), and magnetic characterization by vibrating sample magnetometry (VSM). Furthermore, of excellent promise in semiconductor spintronics, the feasibility of fabricating epitaxially nucleated Fe1-xGax thin films on GaAs having the desired (001) texture was demonstrated. Structural characterization using microdiffraction, high resolution ω - 2θ and rocking curve analysis revealed that the films grown on GaAs(001) are highly textured with <001> orientation along the substrate normal, and the texture improved further upon annealing at 300 °C for 2 hours in N2 environment. This was in contrast to films grown on polycrystalline brass substrates which exhibited undesired <011> texture out-of-plane. Rocking curve analysis on Fe1-xGax/GaAs structures further confirmed that the <001> texture in the Fe1-xGax thin film was indeed due to epitaxial nucleation and growth. A non-linear current-voltage plot was obtained for the Fe1-xGax/GaAs Schottky contacts, characteristic of tunneling injection, and showed improved behavior with annealing.
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    Method Development and Degradation Studies to Verify the Stabilization of a Gallium Prodrug of Epinephrine
    (2021-09) Livezey, Nicholas
    Utilizing the unique and varied properties of metals, such as their redox activity, lability, and net charge, metal-based prodrugs can be designed and optimized for numerous applications. The most prominent usage of metal-based prodrugs has historically been anti-cancer agents, though there have been more recent efforts in the development of theranostic and antimicrobial agents as well. Gallium has promise for extending the scope of metal-based prodrugs, as it has been FDA approved for the treatment of tumors and hypercalcemia. Epinephrine is a compelling target for a gallium-based prodrug as conventional prodrugs are not suitable for the treatment of anaphylactic shock. This is because the prodrugs are inactive during their long half-lives. Additionally, as should mitigate drug degradation from high pH, light, and heat. The development of a novel gallium prodrug of epinephrine establishes the first prodrug treatment of anaphylactic shock, and extends the chemical space of metal-based prodrugs.