Publications

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The development of an electrodeposition process for cobalt/iron (CoFe) alloys with minimal oxygen concentration and controlled stoichiometry is necessary for the advancement of magnetostrictive device functionalities. CoFe alloy films were electrodeposited out of a novel chemistry onto copper test structures enabling magnetic displacement testing for magnetostriction calculations. Using a combination of additives that served as oxygen scavengers, grain refiners, and complexing agents in conjunction with a pulsed plating technique, CoFe films were synthesized at thicknesses as high as 10μm with less than 8 at% oxygen at a stoichiometry of 70-75% Co and 25-30% Fe. X-Ray diffraction (XRD) analysis confirmed that these films had a crystal structure consistent with 70% Co 30% Fe Wairuaite with a slight lattice contraction due to Co doping in the film. A novel characterization technique was used to measure the displacement of the CoFe films electrodeposited, as a function of applied magnetic bias, in order to determine the saturation magnetostriction (λS) of the material. With this chemistry and a tailored pulse plating regime, λS values as high as 172 ± 25ppm have been achieved. This is believed by the authors to be the highest reported value of magnetostriction for an electrodeposited CoFe film.

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Novel low loss photopatternable matrix materials for IR metamaterial applications were synthesized using the ring opening metathesis polymerization reaction (ROMP) of norbornene followed by a partial hydrogenation to remove most of the IR absorbing olefin groups which absorb in the 8-12 {micro}m range. Photopatterning was achieved via crosslinking of the remaining olefin groups with alpha, omega-dithiols via the thiol-ene coupling reaction. Since ROMP is a living polymerization the molecular weight of the polymer can be controlled simply by varying the ratio of catalyst to monomer. In order to determine the optimum photopattenable IR matrix material we varied the amount of olefin remaining after the partial hydrogenation. Hydrogenation was accomplished using tosyl hydrazide. The degree of hydrogenation can be controlled by altering the reaction time or reaction stoichiometry and the by-products can be easily removed during workup by precipitation into ethanol. Several polymers have been prepared using this reduction scheme including two polymers which had 54% and 68% olefin remaining. Free standing films (approx. 12 {micro}m) were prepared from the 68% olefin material using draw-down technique and subsequently irradiated with a UV lamp (365 nm) for thirty minutes to induce crosslinking via thiol-ene reaction. After crosslinking, the olefin IR-absorption band disappeared and the Tg of the matrix material increased; both desirable properties for IR metamaterial applications. The polymer system has inherent photopatternable behavior primarily because of solubility differences between the pre-polymer and cross-linked matrix. Photopatterned structures using the 54% as well as the 68% olefin material were easily obtained. The synthesis, processing, and IR absorption data and the ramifications to dielectric metamaterials will be discussed.

An overwhelming majority of metamaterial designs that have been proposed thus far rely on the use of metallic resonators to afford properties that are unprecedented in nature. Though well suited for applications at radio and microwave frequencies, metals experience severe ohmic losses at higher frequencies rendering their use at such frequencies impractical. Certainly the future of metamaterials lies in their implementation in the visible and long wavelength infrared (LWIR, 8-12 {micro}m). Thus, alternative design protocols and material components tailored specifically for these frequencies are highly attractive. Herein, we present low permittivity, low permeability polymer dielectric materials that are well suited substrates for LWIR-metamaterial applications. These materials lack vibrational absorption bands in the 8-12 {micro}m range are 3D fabrication compatible, photopatternable, and high temperature tolerant. Thus, these materials are ideal for fabrication of 3D metamaterial structures operating in the LWIR and can also serve as negative photoresists for contact lithography applications.