Electrodeposition of multilayered nanostructures for giant magnetoresistance and thermoelectric applications
The electrodeposition of novel materials such as multilayer nanotubes for giant magneto resistance (GMR) applications and bismuth telluride nanotubes for thermoelectric applications are presented in this dissertation. The motivation for the multilayer electrodeposition is the investigation of giant magnetoresistance (GMR), a change in the material resistance in an applied magnetic field as a consequence of antiferromagnetic coupling. The nanowire high aspect ratio geometry allows the measurement of GMR with the current applied perpendicular to the plane (CPP) of the multilayers, which has been theoretically identified as being larger than the GMR in the (CIP) configuration (current in plane of multilayers). The current perpendicular to the plane giant magneto-resistance (CPP)-(GMR) effect makes multilayered nanowires of huge interest as magnetic sensor materials. Electrodeposition is the most efficient method for fabricating magnetic nanowires. In addition to the cost-effectiveness, electrodeposition is one of the few methods that can overcome the geometrical restrictions of inserting metals into very deep nanometric recesses, making it the favored method for nanowire and nanotube fabrication. In this dissertation, the quaternary CoNiFeCu alloy system was investigated in order to electrodeposit multilayered nanowires/nanotubes for GMR effect. Electrodeposited multilayer CoNiFeCu/Cu nanowires and nanotubes were fabricated by pulsed applied electric potential and their giant magnetoresistance (GMR) behavior characterized. The effect of electrolyte concentration on the GMR was investigated. The FeSO4, CoSO4 and NiSO4 concentrations were varied to optimize the GMR and the saturation field of the multilayered nanowires. Nanolayer thicknesses were controlled and varied for commercially viable GMR results. Furthermore, the influence of electrolyte temperature on nanotube formation and the resulting GMR was explored. Micro fluidic magnetic nanoparticles sensors based on CoNiFeCu/Cu GMR nanowires were fabricated for the first time. The test results show that the sensors are highly sensitive to small nanoparticle concentrations. Employing the potentiostatic electrodeposition, nanotubes of bismuth-telluride (Bi2Te3) were obtained. The electrolyte concentration was varied and affected the nanotube formation and the resulting Seebeck coefficients.
electrodeposition, nanowires, nanotubes, gmr, multilayers, sensors, magnetoresistance
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Engineering Science (Interdepartmental Program)