Electrodeposition of FeCoNiCu quaternary system
Electrodeposition is a cost-effective method to produce thin film materials, which have been used widely in the microelectronic industry, and is advantageous to fabricate metal deposits into recessed and curved areas. In this dissertation, FeCoNiCu quaternary alloy system was investigated, both experimentally and theoretically, for fabrication of multilayers, grating structures, and nanowires. Multilayer structures are composed of alternating ferromagnetic and nonmagnetic nanometric layers, and are of interest due to the giant magnetoresistance (GMR) property it possesses, a change in electric resistance in the presence of an external magnetic field. In addition, the compositional modulation, or the composition contrast, in multilayer structures can be used to develop a grating structured mold for the development of a novel nanoimprinting process. FeCoNiCu was investigated as a more general alloy system containing iron-group metals and a nonmagnetic element, Cu, which can be simplified and adapted to any binary or ternary systems. With a dilute tartrate sulfate bath nanometric multilayers were successfully fabricated with pulse plating and GMR value was reported for this electrodeposited system for the first time. A value of -6 % was achieved on rotating disk electrode (RDE) and this maximum occurred when the structure had no preferred crystal phase. Over 40% GMR has been achieved when the multilayer was plated onto a polycrystalline Cu foil. A mathematical model was developed to tailor the deposition process on RDE, and both steady state and nonsteady state cases were simulated. A compositional gradient, which is inherent to a nonsteady state deposition process when the layer size is of nanometer scale was predicted. The quaternary system was explored for other applications. Selective etching of electrodeposited multilayer structures was investigated for different etching solutions. A diluted K2Cr2O7/H2SO4 solution was successfully developed to produce grating structures for a nanoimprinting mold, which was demonstrated with a simple cast molding process. In addition, nanowire plating was explored with different plating schemes. Nanowires of multilayers were successfully fabricated, and the nanometric layer structure was verified. A deviation was observed in the layer thickness from DC plating, as a result of the nonsteady state plating process, consistent with the model developed.
feconicu, modeling, nanoimprinting, nanowire, gmr multilayer, electrodeposition
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