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Selective Electrodeposition of High Aspect Ratio Magnetic and Thermoelectric Materials

October 10, 2017 | 11:00 AM – 12:30 PM
Nedderman Hall 229 | Seminar Flyer

Seminar Speaker

Despina Davis, PhD

Principal Senior Engineer, Advanced Multilayer Interconnect, Raytheon, Space and Airborne Systems

Abstract

In addition to the cost-effectiveness, electrodeposition (electroplating) is one of the few methods that can overcome the geometrical restrictions of inserting metals into very deep nano/micro recesses, making it the method of choice for high aspect ratio nanowire and nanotube fabrication.

Technological applicability of metallic submicron structures has generated tremendous interest because of their industrial potential. The discovery of giant magnetoresistance (GMR) in 1988 by Baibich et al. [Baibich, 1988] in multilayered thin films marked the beginning of an intense research topic. Manufactured materials that exhibit the GMR are used for perpendicular magnetic recording and magnetic field sensors. These magnetic materials make good candidates for computer disk drives, audio-video tape heads, magnetometers, compass systems, etc. Downsizing disk drives involved higher disk drive densities, which in turn requires miniature read heads with increased sensitivity to detect smaller bits and weaker magnetic fields. The GMR effect can also be used for objects’ position detection devices with permanent imprinted magnetization patterns. Robotics and assembly lines use position magnetic sensors that sense a change in magnetic field due to the movement of a magnetized object. Multilayered nanotubes made by alternating ferromagnetic and nonmagnetic layers, are good candidates for the study of perpendicular magneto-transport phenomena and can be used for nanoparticle transport and detection mediums.2,6 GMR sensors possess higher sensitivity, better signal-to-noise ratios, and exhibit minimal mechanical wear since they could be considered contactless sensors.

Thermoelectric phenomena involve the conversion between electrical and thermal energy and its various applications include generation of electric energy for space operation, charge-coupled devices, magnetic sensors, waste heat recovery in automobiles and optoelectronic industries. The nondimensional figure of merit ZT characterizes thermoelectric materials and shows the relationship between the Seebeck coefficient and the electrical conductivity, the thermal conductivity and the absolute temperature. Increasing the power factor and simultaneously decreasing the thermal conductivity is one of the avenues for obtaining high efficiency thermoelectric materials. The nanostructure theoretical-enhanced efficiency is based on the increased density of states and phonon boundary scattering, resulting in a higher power factor and decreased thermal conductivity. The goal 4,5 7-9 is to increase the Seebeck coefficient, the electrical conductivity and power factor using nanostructured thermoelectric Bi2Te3 alloy fabricated by electrodeposition.
In this presentation thermoelectric bismuth-telluride (Bi2Te3) nanostructures have been electrodeposited and optimized for improved Seebeck coefficients to be employed as an external thermocooling component for the magnetic GMR sensing material.1 (US patent 8441255 awarded-Thermocooling of GMR Sensors). Micro fluidic magnetic nanoparticles sensors based on GMR nanowires were fabricated6 and the tested proven to be highly sensitive to low concentration of functionalized nanoparticle.

Bio

Dr. Despina Davis obtained her BS degree in Chemical Engineering from Texas Tech University, and her Masters and Doctorate in Engineering from Louisiana State University (LSU). In 2007, Dr. Davis began her academic appointment in the Chemical Engineering Department & Institute for MicroManufacturing (IfM) at Louisiana Tech University. During her stay at Louisiana Tech, her research funding contribution (PI & Co-PI) was approximately $1million. In 2011, Dr. Davis joined Raytheon Space and Airborne Systems in Dallas where she established a successful record in new process development, technology qualification and tool selection in a state-of-the-art semiconductor manufacturing environment specialized in RF MEMS switches, phase shifters, circulators and multilayer interconnects. Dr. Davis has a solid background in high aspect ratio ferromagnetic nanostructures (nanowires and nanotubes) electroplating for CPP-GMR sensors and high density data storage with more than 20 refereed publications (as corresponding author) in the field of novel materials electrodeposition, sensors and device integration. Dr. Davis conceptualized governmental agencies proposals and executed funded research (NSF, DOE, NASA, DARPA) while supervising research staff performance (nine graduate students) as well as publishing and presenting scientific work.