Galfenol (Fe1-xGax, 10 < x < 40) may be the only smart material that can be made by electrochemical deposition which enables thick film and nanowire structures. This article reviews the deposition, characterization, and applications of Galfenol thin films and nanowires. Galfenol films have been made by sputter deposition as well as by electrochemical deposition, which can be difficult due to the insolubility of gallium. However, a stable process has been developed, using citrate complexing, a rotating disk electrode, Cu seed layers, and pulsed deposition. Galfenol thin films and nanowires have been characterized for crystal structures and magnetostriction both by our group and by collaborators. Films and nanowires have been shown to be largely polycrystalline, with magnetostrictions that are on the same order of magnitude as textured bulk Galfenol. Electrodeposited Galfenol films were made with epitaxial texture on GaAs. Galfenol nanowires have been made by electrodeposition into anodic aluminum oxide templates using similar parameters defined for films. Segmented nanowires of Galfenol/Cu have been made to provide engineered magnetic properties. Applications of Galfenol and other magnetic nanowires include microfluidic sensors, magnetic separation, cellular radio-frequency identification (RFID) tags, magnetic resonance imaging (MRI) contrast, and hyperthermia.

Identifying and characterizing nanoscale crystallographic features is vital for understanding deformation in plasmonic devices and developing more robust plasmonic structures. Here, advanced characterization processes using transmission Electron Back Scatter Diffraction (tEBSD) were developed to analyze thin film crystal structure and its role in plasmonic device stability. The specific crystalline features of interest are film texture, grain boundary configuration and grain size. These results will hopefully contribute to the successful implementation of Heat Assisted Magnetic Recording (HAMR) as well as improve plasmonic device reliability in other applications.[1]

Here, we report the first measurements of magnetostriction as a function of composition for electrodeposited iron-gallium alloys, also known as galfenol. Galfenol is an exciting material due to its large magnetostriction constant (up to 400 ppm) and robust mechanical properties. A wide range of sensors, actuators, and other transducers can be fabricated by taking advantage of galfenol's unique mix of magnetic and mechanical properties. Electrodeposition allows galfenol to be easily integrated into a variety of applications, such as toque sensors with conformal, monolithic active layers. In this work, we examine the underlying factors that influence magnetostriction in electrodeposited galfenol, including crystallinity and composition. Here, we have controlled the film composition, as measured by energy dispersive x-ray spectroscopy, over the range of 5–25% gallium using a single plating bath by varying deposition parameters. This composition range corresponds to the region of largest expected magnetostriction for iron gallium alloys. However, our measured magnetostriction values were significantly lower than the values for single crystal galfenol from literature. The electrodeposited films in this work appeared polycrystalline when measured using x-ray diffraction. When the texture of the film is taken into account, the magnetostriction results closely matched the predicted values. These results show that it is possible to achieve magnetostrictive galfenol thin films over a wide range of compositions using electrodeposition.

Electrodeposition of gold from a basic "fresh" and "used" thiosulfate-sulfite solution containing 0.02 M Na3Au(S2O3)(2) has been investigated on Au and Pt electrodes using various electroanalytical techniques (CV, LSV, RDE), controlled potential electrodeposition, as well as constant current and pulse current deposition. It was proposed that irreversible one electron reduction to gold-run in "fresh" solution-at the Pt electrode starts from Au(S2O3)(SO3)(2)(5-), a mixed gold thiosulfate-sulfite complex with a high stability constant (log beta = 30.8). A diffusion coefficient of 1.77 x 10(-6) cm(2)/s for Au (S2O3) (SO3)(2)(5-) was calculated from the slope of the linear plot i(p)- nu(1/2) obtained with a Pt electrode, which is lower than the value of diffusion coefficient (D = 4.6 x 10(-6) cm(2)/s) obtained for the Au (S2O3)(2)(3-) complex (log beta = 26.0) present in the "used" solution. The voltammograms for gold deposition on the Au electrode were significantly different from those on Pt indicating that the electron transfer was influenced by the coupled chemical reaction. The natures of possible chemical reactions are discussed. (C) 2014 The Electrochemical Society. All rights reserved.

We have investigated a method for measuring the dimensions of an individual multilayered Fe-Ga/Cu nanowire (NW) as it changes with induced magnetization. In this study, we demonstrate the proposed approach and establish this as a viable method for measuring the magnetostrictive behavior of an individual Fe-Ga/Cu NW using atomic force microscopy (AFM). When an external magnetic field (∼300 Oe) was applied perpendicular to the NW axis, the NW length appeared minimized. When a field (∼1000 Oe) was applied parallel to the NW axis, the height profile of the NW was found to be higher than in the case with no parallel external field. Since both ends of the NW were welded to the substrate, the magnetic field induced dimensional change of the NW caused deflection of the NW in the upward direction, which was significant enough to be detected by AFM. An average height difference of 15 nm was measured with and without an applied field which was then used to calculate the magnetostriction of the multilayered NW.

In this paper, we investigate the challenges related to electrodeposition and characterization of magnetostrictive galfenol thin films as well as techniques used to overcome these issues. Successful deposition and evaluation of galfenol thin films is necessary for the design of galfenol based microelectromechanical devices. Stress is a primary concern because thick films and poor adhesion to substrates (e.g., silicon oxide) can lead to delamination and peeling. In addition, magnetostriction measurements require films that are uniform in thickness and composition over the sample area. Various adhesion layers were tested, and delamination was eliminated with Cr/Cu, which provided robust adhesion to the glass substrates used in capacitance bridge measurements. Uniformity and composition were controlled by the use of a rotating disk electrode for electrodeposition, which created a uniform boundary condition across the sample during deposition. The capacitance bridge technique was calibrated with Ni/glass samples, after which a magnetostriction of 140 ppm was measured for Fe83Ga17 films. These results represent the first magnetostriction measurements of electrodeposited galfenol.

In this study, using steady-state electrochemistry at a rotating disk electrode, a deposition mechanism for giant magnetostrictive Fe1−xGax alloys is proposed in which the formation of an adsorbed monovalent [Fe(I)]ads intermediate is determined to be the rate-determining step. In subsequent steps, this intermediate either gets reduced to iron or catalyzes the reduction of gallium by forming an adsorbed [Ga(III)–Fe(I)]ads intermediate. In line with the proposed mechanism, it was experimentally shown that the differences in the mass-transport rates of Fe(II) species determined the thin film composition. Therefore, this study has made possible a controllable and reproducible deposition of Fe1−xGax thin films with compositions in the entire range of interest (15%–30% Ga). As-grown Fe80Ga20 thin films were found to have magnetostriction constants of ~112ppm.