Electrodeposition

"Electrodeposited nickel-tungsten alloys are being considered as a candidate material for components for microelectromechanical systems (MEMS) fabricated by the LIGA (German acronym for lithography, electrodeposition, and forming) technology. In spite of having a useful range of properties including; hardness and strength, better tribological and chemical resistance and improved high temperature resistance as compared with the conventionally used electrodeposited Ni, these alloys possess certain brittleness. In this study, the fracture toughness of Ni-17.5 at%W alloy microcantilever beams (dimension: 60μm × 20μm × 14μm) fabricated by UV lithography and electrodeposition and notched by focused ion beam machining is investigated. Load was applied to the beams using a nanoindenter, which also allowed accurate positioning of the sample. Fracture toughness was calculated from the fracture load assuming a linear elastic behaviour. The Ni-W alloy beams were found to possess a mean fracture toughness of 2.97 MPa √m. The fracture toughness of Ni-W alloy is found to be higher than that of Si another important MEMS material, but considerably lower than that of electrodeposited nickel and nickel base alloys.

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8163165  "

A method for fabricating planar silica substrates via modified chemical vapour deposition (MCVD) and a modified fibre drawing technique is presented. Long lengths of planar material are generated from a single substrate offering a potentially low-cost alternative to existing planar substrate deposition processes. Buried straight and splitting waveguide channels, as well as Bragg gratings, are inscribed in the planar material using direct UV-writing technology, and the results are reported.

The electrodeposition of Pt on glassy carbon (GC) and gas diffusion layer (GDL) surfaces in dilute chloroplatinic acid solutions (10 mM PtCl4 in 0.5 M NaCl) was performed poten tiodynamically in the absence and presence of ultrasound (20 kHz) at various ultrasonic powers (up to 6 W) respectively and at (313  2) K. In our conditions, it was found that platinum electrodeposition is an irreversible process which requires a substantial over-potential to drive the formation of Pt nuclei on the GC and GDL surfaces; however, under sonication  Pt  electrodeposition  becomes  more  facile  due  to  lower concentration  and nucleation  overpotentials  and  overall currents  are  significantly  increased  compared  to silent conditions. It was also observed that the specific electrochemical surface area (SECSA) was significantly affected for Pt/GC and Pt/GDL electrodes prepared in the presence of rotation (GC only) and under sonication compared to those prepared under silent conditions. This finding was explained to be due to both larger and agglomerated platinum nanoparticles formed on the GC and GDL surface caused by forced convection. It was also found that ultrasound produced larger Pt nanoparticles on GC electrodes than those on GDL electrodes.

"The co-electrodeposition of copper and indium from a pH 3 tartrate bath onto 4.8 cm × 2.5 cm Mo and MoSe2 substrates is studied and conditions are optimised for CuIn alloy films. Selenisation at ca. 500 °C for 30 min in selenium vapour gives CuInSe2 (or CISe). Mapping using the photo-electrochemical reduction of Eu(NO3)3 is used to asses the relative photoactivity as a function of position and surface treatment.

Etching of detrimental CuxSe phases is investigated with 5% and 0.5% (w/w) aqueous KCN. The slower 0.5% (w/w) KCN etch allows better process control, and re-annealing at 500 °C for 30 min followed by further etching significantly improved the photo-activity. However, over the large area local pinhole recombination effects are substantial. An alternative low temperature film optimisation method is proposed based on (i) KCN over-etch, (ii) hypochlorite (5%, w/w) pinhole removal (Mo etch), and (iii) a final KCN etch to give good and more uniform activity."

In the present work, a novel process for Fe-Ga thin films electrodeposition is addressed and the magnetic properties of the films are studied. The electrodeposition was carried out under ambient conditions using an ionic liquid electrolyte consisting of a mixture of choline chloride and ethylene glycol in the molar ratio 1:2, containing 0.3 M FeCl2 and 0.1 M GaCl3, either in the absence or in the presence of oxalic acid at 4 or 17 mM concentration. The effect of oxalic acid on the discharge reaction of the single ionic species Fe2+ and Ga3+ and on their codeposition was investigated by linear sweep voltammetry, suggesting a specific action of oxalic acid on the cathodic reduction of Ga3+ ionic species. Depending on deposition potential and oxalic acid concentration, alloy films with Ga content variable in the range up to about 20 at.% could be obtained. The Fe-Ga thin films showed a disordered body-cantered cubic phase (A2) with (110) preferred orientation and columnar microstructure, with a drastic change from pyramidal to granular surface morphology revealed raising the deposition potential. No superlattice reflections, indicating the formation of the D03 structure, were observed. A vibrating sample magnetometer was employed to measure hysteresis loops by applying longitudinal and transversal magnetic field on the Fe-Ga film plane. The saturation magnetization of as-deposited film reached 1.75 T for Fe83Ga17 thin films, confirming that good quality films were obtained. For the same alloy composition, the coercivity values were 67 Oe and 200 Oe, with applied field parallel and perpendicular to the film plane, respectively.

"Fe-0.96mass%C and Fe-15.4mass%Ni-0.70mass%C alloys with hardness of 810 and 750 HV respectively have been electrodeposited at 50°C from sulphate based baths containing a small amount of citric acid and L-ascorbic acid. Differential scanning calorimetry of the electrodeposited samples has been carried out in the temperature range of 293-725 K in argon atmosphere. Electrodeposited pure Fe is also investigated for comparison purposes. The DSC curves of both alloys contain two exothermic peaks: at about 411 K and 646 K for the Fe-C alloy, and 388 K and 639 K for the Fe-Ni-C alloy. These peaks are irreversible and do not appear during a second thermal cycling. The lower temperature peaks (designated as I) have been attributed mainly to the formation of ε/η-Fe 2C (first stage of tempering), while the higher temperature peaks (designated as III) are ascribed predominantly to θ-Fe 3C formation (third stage of tempering). The presence of these peaks in the DSC curves confirms that electrodeposited Fe-C and Fe-Ni-C alloys are in a metastable state, where carbon atoms are entrapped in the iron lattice. The decomposition sequence of electrodeposited Fe-C and Fe-Ni-C alloys is found to follow the same general pattern as that of thermally prepared martensite. Attempt has been made to estimate the activation energy values for the reactions associated with the DSC peaks of the electrodeposited alloys and these values are compared with the available data on thermally prepared martensite.

http://link.springer.com/content/pdf/10.1023%2FA%3A1017931106376.pdf  "

"Nanocrystalline nickel-tungsten alloys have great potential in the fabrication of components for microelectromechanical systems. Here the fracture toughness of Ni-12.7 at.%W alloy micro-cantilever beams was investigated. Micro-cantilevers were fabricated by UV lithography and electrodeposition and notched by focused ion beam machining. Load was applied using a nanoindenter and fracture toughness was calculated from the fracture load. Fracture toughness of the Ni-12.7 at.%W was in the range of 1.49-5.14 MPa √m. This is higher than the fracture toughness of Si (another important microelectromechanical systems material), but considerably lower than that of electrodeposited nickel and other nickel based alloys.

http://ac.els-cdn.com/S0040609012001915/1-s2.0-S0040609012001915-main.pdf?_tid=247c308a-eeb8-11e2-a1f2-00000aab0f6c&acdnat=1374048723_de7be340b0dc4a56be9a64dc1bd8e3b9  "

"Iron-carbon based hard, martensitic alloys are usually produced by conventional high temperature heat treatment. In the present work, the galvanostatic electrodeposition method has been employed to obtain hard Fe-0.96 mass % C and Fe- 15.4 mass% Ni-0.70 mass% C alloys at around room temperature. The alloys have been investigated by SEM, XPS, XRD, and microhardness measurements, and their magnetic properties have been studied by vibrating sample magnetometer. The as-deposited alloys were found to possess high mechanical hardness, 750-810 HV. Both alloys exhibit a smoother surface morphology as compared to a non-alloyed iron film obtained under similar electrochemical conditions. The coercive force of the as-deposited Fe-C and Fe-Ni-C alloys is 3930 and 494 A.m -1 respectively. In comparison, pure iron film deposited under similar conditions possesses a coercive force of 1592 A.m -1. The Fe-Ni-C alloy has a combination of high mechanical hardness and relatively soft magnetic properties, which may be of interest in potential applications requiring both soft magnetic properties and improved tribological performance. The effects of annealing on the behavior of the alloys are discussed.

http://journals.cambridge.org/action/displayAbstract;jsessionid=E9656E56281969A7027FEC77E6E105A0.journals?fromPage=online&aid=8209807  "

"Eutectic Sn-Bi alloy is gaining considerable attention in the electronic packaging industry because of its favorable properties such as low melting temperature, good wettability, and good mechanical properties. Miniaturization of electronic devices requires small solder bumps, a few tens of micrometers in diameter. Electrodeposition is a reliable technique for the deposition of small volume of solder. This work focuses on the formation of eutectic Sn-Bi solder by reflowing a metal stack containing sequentially electrodeposited Sn and Bi layers. The effects of layering sequence on the composition and microstructure of the resulting alloy is investigated. Irrespective of the layering sequence, a homogeneous microstructure is achieved after reflow. The microstructure of the reflowed samples is the same as that of a metallurgically processed Sn-Bi alloy. Near-eutectic alloy with the composition Sn-54.6 wt% Bi is obtained by the sequential electrodeposition method.

http://link.springer.com/content/pdf/10.1007%2Fs10854-012-1055-4.pdf  "

"Purpose - The purpose of this paper is to enhance the understanding on the electrodeposition of various lead (Pb)-free solder alloys, so that new studies can be carried out to solve processing issues. Design/methodology/approach - The paper reviews the available reports on the electrodeposition of tin (Sn)-based solder systems and identifies the challenges in this area. Findings - Compositional control remains a major challenge in this area, where the achievement of desired composition for binary and ternary alloys is subjected to uncertainties. The use of chelating agents in the bath and optimization of parameters can assist the achievement of near-desired alloy composition. Acidic plating baths are preferred due to their compatibility with photoresists but oxidation of stannous ions causes poor bath stability. Antioxidants, reducing agents and low oxygen overpotential anodes can suppress the oxidation rate and increase the lifespan of plating baths. Apart from chelating agents and antioxidants, various categories of additives can be added to improve quality of deposits. Surfactants, grain refiners and brighteners are routinely used to obtain smooth, fine-grained and bright deposits with good thermo-mechanical properties. Originality/value - The paper provides information on the key issues in electrodeposition of Pb-free solder alloys. Possible measures to alleviate the issues are suggested so that the electrodeposition technique can be established for mass production of a wider range of solder alloys.

http://www.emeraldinsight.com/journals.htm?issn=0954-0911&volume=25&issue=2&articleid=17084668&show=pdf  "

"Sulfuric acid based Sn-Ag plating baths were developed to study the individual as well as synergistic effects of thiourea (TU) and gelatin on the characteristics of Sn-Ag deposits. Electrochemical behavior of each bath was investigated by cathodic polarization studies. Results showed that the deposition potential gap of both elements was reduced by both additives, hence allowing co-deposition of Sn-Ag to occur. In this study, TU increases Ag composition and changes deposits microstructure. Low content of gelatin inhibits Ag deposition but high content of gelatin results in enhanced Ag deposition. Microstructure of deposits has been improved by the synergistic effects of these two additives. Near-eutectic composition of Sn-4.0 wt.% Ag is achieved with the aid of 2g/L of TU and 1g/L of gelatin at a current density of 10mA cm -2.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6320518  "

"The electrodeposition of Cu/Ni compositionally modulated multilayers with sublayer thickness in the nanometer range has been carried out. The deposition was conducted under galvanostatic conditions using dual-bath technique. The structure of the multilayers was characterized by scanning electron microscopy, and conventional and high resolution transmission electron microscopy. Cu/Ni multilayers with distinct and continuous sublayers in the range of 100 to <5 nm can be produced by dual-bath electrodeposition. Cu and Ni sublayers grow epitaxially on top of one another. The local variation in the growth rate of copper leads to a faceted morphology of the multilayers. The extent of this faceting is reduced as the sublayer thickness is decreased. A surface reaction like oxidation during transfer of the substrate does not adversely affect the crystallographic continuity at the interfaces between sublayers. The thin-film formation is discussed based on available growth models.

http://jes.ecsdl.org/content/141/1/230  "

"Hard Fe-C based alloys, Fe-0.96 mass% C and Fe-15.4 mass% C having a microhardness of 810 and 750 HV, respectively, are electrodeposited from sulfate-based baths at 50°C. The Mössbauer spectra consist of high intensity sextet due to ferromagnetic Fe. The linewidth of the sextet is larger for alloys than for the pure Fe, indicating an increased effective field at different Fe sites in the alloys. Absence of any low intensity sextet, which is attributable to the Fe atoms close to the C atoms at the octahedral c-axis position, suggests that the electrodeposited alloys are in an advanced state of aging. Simultaneous H evolution during electrodeposition is believed to play an important role in determining the nature of the alloys.

http://ac.els-cdn.com/S1359646200006291/1-s2.0-S1359646200006291-main.pdf?_tid=20d4e634-eeb8-11e2-bd53-00000aacb361&acdnat=1374048716_af284a2ea98bec1613e32f79185c8480  "

"Structural and chemical investigations on electrodeposited nickel-phosphorous alloy coatings by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) are described. Electrodeposition of nickel-phosphorous coatings has been carried out galvanostatically in a hypophosphite bath at two different current densities, namely 20 and 80 mA cm -2. XRD has shown a broad peak indicating an amorphous structure in both cases. XPS shows the presence of Ni 2P compound. XPS also reveals the amount of phosphorous in both coatings to be around 10.20 wt.%. SIMS has shown that the coating deposited at lower current density (20 mA cm -2) has a broad coating-substrate interface, possibly due to some porosity in this coating. The presence of some oxygen contamination at the coating-substrate interface is also evidenced through SIMS in both cases. The usefulness of XPS and SIMS in the characterization of electrodeposited coatings is demonstrated.


http://ac.els-cdn.com/0040609095082174/1-s2.0-0040609095082174-main.pdf?_tid=99464504-eeb8-11e2-8d42-00000aacb35e&acdnat=1374048918_4c690559864f4de8af1f8858bf152664  "

"Fretting wear behaviour of electrodeposited Cu/Ni multilayer films with 10 and 5 nm thick sublayers has been investigated against a hardened steel ball as the counter body and compared with that of the constituents, Cu and Ni. The wear tests were carried out by using a ball-on-flat geometry at a translation frequency of 8 Hz and slip amplitude of 100 μm. Friction force was recorded on line during the tests. At the end of the tests, the wear scars were examined by laser surface profilometry, scanning electron microscopy and energy dispersive X-ray microanalysis. It has been observed that the frictional and wear mechanisms are very different for copper, nickel and Cu/Ni multilayers. Fretting of copper creates a relatively smooth wear scar mainly by mechanical ploughing of the asperities on steel counterbody (abrasive wear) and shows a very little third body interaction. Fretting of nickel involves adhesive wear resulting in a large transfer of steel to nickel, which is attributed to the strong chemical interaction between nickel and the steel counterbody. Fretting on multilayers involves a strong third body interaction resulting in ploughing mainly by debris (abrasive wear). The coefficient of friction is approximately 0.45 for copper, and approximately 0.8 for nickel as well as for multilayers. The values of the coefficient of friction for nickel and Cu/Ni multilayers found under the present fretting conditions are approximately double the corresponding values reported earlier for sliding wear conditions. It has been found that Cu/Ni multilayer is more resistance to fretting wear than the constituents, copper and nickel. Furthermore, the fretting wear resistance of Cu/Ni multilayers with 5 nm thick sublayer is better than that of the multilayers with 10 nm thick sublayers.

http://www.sciencedirect.com/science/article/pii/S0040609003010897  "

Electrodeposited nanocrystalline nickel-tungsten alloys are being investigated as an attractive alternative to electrodeposited nickel for applications involving fabrication of micro electro mechanical systems (MEMS). Ni-W alloys are also being considered as an environmentally friendly alternative to hard chrome plating in some cases. In applications involving sliding contacts such as in micro-gears in MEMS, mould inserts, etc., tribological properties of Ni-W alloys would be of relevance. In this work, the sliding friction and wear characteristics of Ni-W alloys with different tungsten contents were investigated and compared with that of nickel film deposited from sulphamate bath commonly used in microfabrication. For wear tests, Ni-W alloy films of about 5-7 μm, deposited from ammonia-citrate baths on copper substrates were employed. The alloy films possessed W contents in the range of 8.4-12.7 at.% and had an average grain size of about 20 nm. Wear tests were conducted in a pin-on-disc type tribometer under un-lubricated conditions. All the wear tests were carried out at room temperature in air with a controlled relative humidity of 50 ± 5% at a normal load and linear sliding speed of 1 N and 3 cm s-1, respectively. Hardened steel balls were used as the counter body. Friction force was recorded online during the wear test. Wear damage on Ni and Ni-W alloy films was estimated from the width of the wear track and the wear rate of the counter body was calculated from the worn volume. Results show that Ni-W alloys have somewhat lower friction coefficient against steel counter body as compared with that of the nickel-steel pair. Addition of tungsten to nickel is also seen to result in an improvement in wear resistance. Friction and wear mechanisms operative in Ni-W alloys sliding against steel are discussed.

The dissolution behavior of electrodeposited Zn was studied in the electrowinning solution containing an impurity such as Ag, Al, As, Cd, Co, Cu, Fe, Ge, Ni, Pb or Sb. The dissolution occurs when the operating current density becomes substantially lower than the critical current density for Zn deposition onto Zn electrode. The simulation experiments revealed that the decrease in the operating current density should be resulted from such two factors that the practical current density decreased due to the increased cathode surface area and that the critical current density increased in the presence of impurity in the solution. The impurities were classified into four groups according to their effects, previously reported by the present authors, on the critical current density. The time-dependence of Al cathode potential was measured at three levels of current densities in the solutions containing three different amounts of each impurity. The effects of each group of impurities on the electrodeposition and dissolution behaviors of Zn were discussed by considering above two factors. Further the dissolution behavior during the commercial electrowinning operation, in which the impurity concentration was usually time-dependent, was briefly referred.

Recently, an intensive attention has been paid to the electrodeposition of Zn-Cr alloy in the field of the production of super-highly corrosion-resistant alloy plated steel sheets for the next generation. In this study the electrodeposition of Zn-Cr alloys from the sulfate baths was conducted to investigate the codeposition mechanism of Cr with Zn. As a result, Cr was codeposited with Zn at higher current densities in both polyethyleneglycol (PEG)-free and PEG-containing baths. However, PEG made it possible to reduce Cr3+ to the metallic state and Cr existed in the form of Cr(III) hydroxide in the deposits obtained from PEG-free bath. The measurements of the partial polarization curve of Zn and the pH in the cathode layer revealed that PEG acted as a polarizer to shift the cathode potential to the reduction potential of the composited hydroxides of Zn and Cr formed due to the pH rise in the cathode layer.