The structure of noncrystalline electrodeposited Ni–P alloys, 73.8–81.4 at.% Ni, has been investigated by x‐ray scattering and by physical density measurements. The x‐ray interference functions, I(k), are qualitatively inconsistent with those calculated for fcc‐, hcp‐, and Ni3P‐type crystallites. Calculated radial distribution functions RDF(r) indicate that the alloys have a better defined short‐range order than that observed in liquid noble metals above their melting points. The observed I(k) are very similar to the I(k) calculated by Dixmier, Doi, and Guinier [in Physics of Noncrystalline Solids, J. A. Prins, Ed. (North‐Holland Publ. Co., Amsterdam, 1965), p. 67] from their model. However, the parameters needed to fit the experimental results are inconsistent with the atomic sizes expected for nickel and phosphorus. The noncrystalline alloys are between 0.6% and 1.4% less dense than the corresponding mixtures of fcc Ni and Ni3P, both of which are essentially close packed. A grain boundary density defici...

Structural Investigation of Noncrystalline Nickel‐Phosphorus Alloys

Effects of added surfactants in the acidic hypophosphite plating baths on the properties of the resulting electroless nickel−phosphorus (Ni−P) deposits on the brass substrates were studied. The surface appearance and microstructures were examined under a reflective optical microscope and a scanning electron microscope equipped with an in situ energy-dispersive X-ray spectroscopy with which the phosphorus contents were measured. The deposition rate and the corrosion rate of the Ni−P deposits were estimated respectively from the weight gains and losses after a period of time. It is found that the addition of suitable amounts of surfactants can increase the deposition rate up to 25% and reduce the formation of the pores on the surface of Ni−P alloys, as well as enhance the corrosion resistance of the deposits. The corrosion rate of the Ni−P alloys in 10 wt % HCl was determined. The corresponding corrosion rate fits well as an empirical power function having an order of near 1/3 in the amount of dissolved Ni−...

Effects of Surfactants in an Electroless Nickel-Plating Bath on the Properties of Ni−P Alloy Deposits

Electron microscopy has been used to study the structure of Ni-P electrodeposited thin films with 7, 12, 20 and 22 at. pct P. For the crystalline as-deposited films with 7 and 12 at. pct P (low P films), the crystal structure is fcc and the grains are a supersaturated solid solution of P in Ni. Grain size decreases with increasing P content; the present findings agree with previous ones. For “amorphous” as-deposited films with 20 and 22 at. pet P (high P content films) the amorphous phase is not completely homogeneous and there are regions in which small microcrystals exist. Electron beam heating a low P con-tent film causes the crystalline array of supersaturated Ni grains to decompose to an equilibrium mixture of Ni and Ni3P; both types of grains are randomly oriented. Electron beam heating a high P content film causes the amorphous regions to undergo several complex transformations. The first reaction to occur is: Amorphous (Ni-P) -NixPy + Ni (random) where NixPy is a newly discovered phase with a variable composition. Further beam heating causes a second transformation to equilibrium phases: NixPy + Ni → Ni3P + Ni (random). The microstructure resulting from the above transformations depends on variations in composition of the as-deposited specimens, rates of heating and temperature gradients. The mode of phase transformation in microcrystalline regions and amorphous regions is distinctly different. Crystallization in amorphous regions occurs by a nucleation and growth of NixPy, and Ni; a crystallization front is seen to advance into the amorphous re-gion. Crystallization in microcrystalline regions occurs by nucleation and growth of the Ni3P phase and grain coarsening of the Ni phase. No distinct crystallization front is ob-served.

Electron microscopy of crystalline and amorphous Ni-P electrodeposited films: In-situ crystallization of an amorphous solid

The electrochemical behaviors of semiconductor electrodes on which a very small amount of metal is electrodeposited have been studied. The cathodic photocurrent-potential curve for the p-type GaP or Si electrode is shifted to the 0.2–0.3V more positive potential by the deposition of platinum. The cathodic current-potential curve for the n-type GaP electrode is also shifted similarly, but the anodic current-potential curves and the flat band potentials for both the p- and n-GaP electrodes are not changed. From these results and those on the effects of other metals (Pd, Ni or Cu), it is concluded that the above-mentioned shifts are due to the catalytic actions of the deposited metals on the hydrogen evolution reaction at the semiconductor electrodes. A tentative model explaining this effect is presented.

The Catalytic Effect of Electrodeposited Metals on the Photo‐Reduction of Water at p‐type Semiconductors

Electroless (autocatalytic) plating involves the presence of a chemical reducing agent in solution to reducemetallic ions to the metal state. The name electroless is somewhat misleading, however. There are no external electrodes present, but there is electric current (charge transfer) involved. Instead of an anode, the metal is supplied by the metal salt; replenishment is achieved by adding either salt or an external loop with an anode of the corresponding metal that has higher efficiency than the cathode. There is therefore, instead of a cathode to reduce the metal, a substrate serving as the cathode, while the electrons are provided by a reducing agent. The process takes place only on catalytic surfaces rather than throughout the solution (if the process is not properly controlled, the reduction can take place throughout the solution, possibly on particles of dust or of catalytic metals, with undesirable results). Brenner and Riddell [1] invented electroless Ni plating in 1946 rather accidentally when they observed that the additive NaH2PO2 caused apparent cathode efficiencies of more than 100% in a nickel electroplating bath. This led them to the correct conclusion that some chemical reduction was involved. Further research resulted in the development of the original process that the inventors named electrodeless plating. The name soon lost the de, and later the name autocatalytic was formally adopted, although electroless is still widely used. The words are synonymous. Autocatalytic plating is defined as the deposition of a metallic coating by a controlled chemical reduction that is catalyzed by the metal or alloy being deposited. Such plating has been used to yield deposits of Ni, Co, Pd, Cu, Au, and Ag as well as some alloys containing these metals plus P or B. Electroless Cr deposition has also been claimed. Chemical reducing agents have included NaH2PO2 (the one originally used by the inventors for Ni and Cu deposition and still the most important and widely investigated), formaldehyde— especially for Cu—hydrazine, borohydrides, amine boranes, and some of their derivatives. Electroless plating possesses several characteristics not shared by other techniques, and that accounts for its ever-growing popularity. Its throwing power is essentially perfect, at least on any surface to which the solution has access, with no excessive buildup on edges and projections. Deposits may be less porous than electroplates and hence have better corrosion resistance. Power supplies, electrical contacts, and the other apparatus necessary for electroplating are not required. The process is usually an integral and necessary step in plating on nonconductors such as plastics (see Chapter 15 of this volume). The process is particularly important in the printed circuit industry. Some electroless deposits have unusual or even unique magnetic properties. Experience shows that each substrate requires its own specific techniques; depositing active metal onto the surface of a non(semi)conductor is still somewhat of an art. The surface preparation (i.e., cleaning process) requires very careful selection and application. It must be stressed that cleaning may affect the porosity of the metal deposit. Residues from cleaners and deoxidizers may create inactive spots that will not initiate electroless deposition. This may result in the necessity to have a thicker deposit before continuity is achieved. In extreme cases continuity is never reached. In general, deposition requires one or more of the following steps (see Fig. 18.1): (1) cleaning, (2) surface modification, (3) sensitization, (4) catalyzing or (30) catalyzing, and (4) activation (acceleration). Rinsing is required between the steps. We refer to the steps 3 and 4 (shown in Fig. 18.1) as sensitization and catalyzing. By these terms we mean

Electroless Deposition of Nickel

The nucleation, early growth, and structure of Ni‐P on activated dielectric substrates were studied. The treatment was found to provide small catalytic sites on the substrate, serving as the nuclei for Ni‐P growth. The average diameter of catalytic sites was estimated to be less than 10Aa. The microscopic time rate of Ni‐P growth on the nuclei was found to be constant and the growth to be isotropic. The resulting Ni‐P deposit in the early stages of growth consists of circular islands. The surface density σ of islands were affected by activation. In later stages of growth, the circular Ni‐P islands merged to form a continuous film. The critical film thickness at which continuity is attained is shown to be a function of σ. The structure of as‐deposited islands, as well as that of fresh continuous film, was determined by electron diffraction to be liquidlike.

https://iopscience.iop.org/article/10.1149/1.2410991/pdf

J. P. Marton

Papers

The Nucleation, Growth, and Structure of Thin Ni‐P Films