Electrodeposition of gold from a basic "fresh" and "used" thiosulfate-sulfite solution containing 0.02 M Na 3 Au(S 2 O 3 ) 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(S 2 O 3 )(SO 3 ) 2 5− , a mixed gold thiosulfate -sulfite complex with a high stability constant (log β = 30.8). A diffusion coefficient of 1.77 × 10 −6 cm 2 /s for Au (S 2 O 3 ) (SO 3 ) 2 5− was calculated from the slope of the linear plot i p -ν 1/2 obtained with a Pt electrode, which is lower than the value of diffusion coefficient (D = 4.6 × 10 −6 cm 2 /s) obtained for the Au (S 2 O 3 ) 2 3− complex (log β = 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.Electrodeposition of gold is the metallization process of choice for interconnects, and electrical contacts in compound semiconductors, as well as optoelectronic and biomedical applications as described in recent reviews. 1-3 In addition to useful electrical properties gold also shows excellent plasmonic properties at room temperature, but is susceptible to deformations caused by high energy densities encountered in plasmonic devices. 4 Traditional cyanide-based gold plating solutions are becoming increasingly unpopular for obvious toxicity concerns including possible liberation of toxic HCN gas in the reaction with acids, worksite safety, effluent treatment etc. Excess of cyanide ions, liberated during electrochemical reduction of the Au(CN) 2 − complex, can attack photoresist, resulting in lift-off of the resist and deposition of extraneous gold underneath the interface between resist and substrate. 3,5-7 In order to address these shortcomings, new non-cyanide solutions including sulfite, thiosulfate, mixed sulfite-thiosulfate, and organic additives as a solution-stabilizers have been evaluated. 1-3 Compared to cyanide, these non-cyanide electrolytes are environmentally friendly, but suffer from SO 2 , and colloidal sulfur formation in neutral and acidic media. 5-7 The instability of sulfite and thiosulfate electrolytes can be improved through addition of organic and inorganic bath stabilizers. 6-8 Thiosulfate plating solutions are unstable under neutral and acidic conditions due to thiosulfate decomposition and formation of "colloidal" sulfur. 2"Colloidal" sulfur is also formed by the protonation of excess S 2 O 3 2− ions according to the following equation:The precipitation of "colloidal" sulfur which occurs with precipitation of all gold thiosulfate complexes is catastrophic when it happens in an industrial electrodeposition tool. The addition of sulfite into the thiosulfate s...

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.

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Articles you may be interested inElectrodeposition and characterization of magnetostrictive galfenol (FeGa) thin films for use in microelectromechanical systems

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.