Structural electroless alloys

The structures of electroplated hard alloys have been less extensively studied than those of similar electrolessly deposited materials. Sallo and co-workers [118-120] have investigated the relationship between the structure and the magnetic properties of CoP and CoNiP electrodeposits. The structures and domain patterns were different for deposits with different ranges of coercivity. The lower-f/c materials formed lamellar structures with the easy axis of magnetization in the plane of the film. The high-Hc deposits, on the other hand, had a rod-like structure, and shape anisotropy may have contributed to the high coercivity. The platelets and rods are presumed to be isolated by a thin layer of a nonmagnetic material. 

O Sullivan describes the fundamental theory, mechanistic aspects and practical issues associated with autocatalytic electroless metal deposition processes. Current approaches for gaining fundamental understanding of this complex process are described, along with results for copper, nickel and various alloys. Emphasis is placed on microelectronic applications that include formation of structures that are smaller than the diffusion layer thickness which influences structure formation. 

There are four types of fundamental subjects involved in the process represented by Eq. (1.1) (1) metal-solution interface as the locus of the deposition process, (2) kinetics and mechanism of the deposition process, (3) nucleation and growth processes of the metal lattice (M a[tice), and (4) structure and properties of the deposits. The material in this book is arranged according to these four fundamental issues. We start by considering the basic components of an electrochemical cell for deposition in the first three chapters. Chapter 2 treats water and ionic solutions Chapter 3, metal and metal surfaces and Chapter 4, the metal-solution interface. In Chapter 5 we discuss the potential difference across an interface. Chapter 6 contains presentation of the kinetics and mechanisms of electrodeposition. Nucleation and growth of thin films and formation of the bulk phase are treated in Chapter 7. Electroless deposition and deposition by displacement are the subject of Chapters 8 and 9, respectively. Chapter 10 contains discussion on the effects of additives in the deposition and nucleation and growth processes. Simultaneous deposition of two or more metals, alloy deposition, is discussed in Chapter 11. The manner in which... 

It had previously been reported that the structure of electroless NiP alloy films containing less than 15 at% phosphorus is crystalline, while the structure of films containing more than 15 at% is amorphous [26]. The structure of NiWP and NiMoP depends on the phosphorus content. NiP, NiWP, and NiReP, for instance, become amorphous if their phosphorus content exceeds a certain value. NiReP and NiWP, as shown in Tkble 6 and 7, are amorphous over the entire range of compositions. The structure of NiReP film plated from a bath containing 0.03 mol dm of NH4Re04 in particular is peculiarly amorphous, in spite of the fact that its phosphorus content is only 5 at%. This film contains as much as 44 at% of rhenium. 

It is usual to compare the infrared spectra of the electrochemically treated amorphous alloys to those of the chemically or thermally (at 380°C) prepared spinels to ascertain the nature and composition of the compound. With this methodology, it can be demonstrated that the hydrous oxide coating acts as a precursor of a spinel structure either from the electrolessly deposited amorphous alloys or after the square-wave potential treatment. 

In the IC industry electroless metal deposition can be used for contact filling, via filling, and conductor patterns. In micromachining electroless deposition can be used for all of the same purposes but also to make structural microelements from a wide variety of metals, metal alloys, and even composite materials. 

Wan] Wang, L.L., Zhang, B.W., Yi, G., Ouyang, Y.F., Hu, W.Y., Structure and Crystallization of Amorphous Fe-Mo-B Alloys Obtained by Electroless Plating , J. Alloys Compd., 255(1-2), 231-235 (1997) (Crys. Structure, Morphology, Phase Relations, Thermodyn., Experimental, 5)... 

Preferential segregation of certain elements from dense alloy membranes can also result in degradation of the performance of H2 permeation membranes. For example, Pd-Ag films ( 2.4%Ag, 20-26 pm thick) were deposited by sequential electroless plating onto porous tubular stainless steel substrates with AI2O3 oxide layers to modify the substrate pore size and to prevent intermetallic diffusion of the stainless steel components into the Pd-Ag layer (Bosko et al., 2011). Composite membranes annealed at temperatures of 500-600°C were characterized for film structure (XRD), morphology (SEM), bulk and surface component distribution (EDS, XPS), and H2 permeance. Composition measurements within the Pd-Ag layer revealed preferential segregation of the Ag component to the top surface. This result is consistent with the lower surface free energy of Ag. 

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