(169c) Electrodeposited FeNiCo and FeNiCoCu Microposts and Nanowires

Electrodeposited FeNiCo alloys are of interest as electronic magnetic components and as an element of a bimorph temperature sensor. While most electrodeposited metals and alloys exhibit high thermal expansion coefficients (CTE), Fe-rich, FeNiCo alloys that consist of 64 wt % Fe, 31 wt % Ni, and 5 wt % Co have characteristically low CTE values as bulk films, referred to as Super Invar. Fabricating and controlling these elements with uniform composition into recessed geometries is not straightforward because of their preferential deposition of the less noble metal. Our work addresses the conditions to obtain a low CTE Super Invar-like alloy that is electrodeposited into micro- and nano-recesses. Guiding conditions were determined using a rotating Hull cell. The micro-recess electrode array was fabricated with X-ray lithography and the nano-recess array was demonstrated with porous alumina membranes. Micropost arrays were electrodeposited using different pulsing waveforms and the composition distribution along the length of the microposts examined. The corresponding CTE was also determined; the FeNiCo microposts exhibited negative CTEs in the axial direction, i.e., the micro-posts shrink with a temperature increase, unlike bulk equivalents. Electrodeposition of nanowires composed of Super Invar-like composition was also explored. Addition of copper ions to the electrolyte and subsequent deposit enables the design of a multilayered structure having the potential to tailor the CTE. It was observed that the copper affected the deposition rates of Fe, Ni, and Co differently, altering the deposit composition.