Electroless crystallization

Films of CoB have been prepared by electroless deposition. Chang et al. [25] deposited magnetically soft amorphous films, which could be annealed to give materials with an Hc of 250 Oe. Depending on the annealing temperature, the films crystallized as the hep or fee modifications of Co. Matsui and co-workers [22] obtained crystalline materials in the as-deposited state, the crystalline characteristics being determined by processing conditions. A maximum HQ of 300 Oe was observed for films with 10.0 preferred orientation. 

In this chapter we discuss the electrochemical model of electroless deposition (Sections 8.2 and 8.3), kinetics and mechanism of partial reactions (Sections 8.4 and 8.5), activation of noncatalytic surfaces (Section 8.6), kinetics of electroless deposition (Section 8.7), the mechanism of electroless crystallization (Section 8.8), and unique properties of some deposits (Section 8.9). 

A comparison of the results using this method and the rate of electroless copper deposition determined gravimetrically shows that the best results are obtained with the Le Roy equation applied to the polarization data in the anodic range. It is interesting to note that here, in the metal deposition as in the corrosion (9), the partial reaction, which does not involve destruction or building of a crystal lattice of metal substrate, gives better results (this is hardly surprising, of course). 

Electroless crystallization proceeds in two basic stages (1) the thin-film stage (up to 3 p.m) and (2) the bulk stage. 

After discussing adsorption, we discuss the effects of additives on the kinetic parameters of the deposition process and on the elementary processes of crystal growth. The general effect of additives on electroless deposition is discussed in Section 8.4. 

Electrochemical properties of silicon single crystals, usually cuts of semiconductor wafers, have to be considered under two distinct respects (1) As an electrode, silicon is a source of charge carriers, electrons or positive holes, involved in electrochemical reactions, and whose surface concentration is a determining parameter for the rate of charge transfer. (2) As a chemical element, silicon material is also involved in redox transformations such as electroless deposition, oxide generation, and anodic etching, or corrosion processes. 

Mindt [29] described some properties of these films (thicker electroless films, not the initial purely CD ones). Electron diffraction showed that the film was a-PbOi. The crystal (more correctly the particle) size was found, by electron microscopy, to be ca. 200 nm. The carrier density, measured by the Hall effect, was ca. 10 cm. The resistivity was somewhat dependent on the pH of deposi-... 

Schlesinger and Marton (15) studied the nucleation and growth of electrolessly deposited thin nickel (Ni-P) films. These studies were later extended and complemented by the studies performed by Cortijo and Schlesinger (19, 20) on radial distribution functions (RDFs). RDF curves were derived from electron diffraction data obtained from similar types of films as well as electrolessly deposited copper ones. Those studies, taken together, have elucidated the process of crystallization in the electroless deposition of thin metal films. 

In the initial stages of the electroless deposition the average TDC density increases with the time of deposition in this time interval the nucleation is the predominant process. Later, the average TDC density reaches a maximum and then decreases with time. In the time interval of decreasing TDC density, the coalescence is the predominant crystal-building process. A continuous electroless film is formed by lateral growth and coalescence of TDC (40). 

The design of the interstices filling in colloidal crystals with appropriate media and subsequently fluid-solid transformation is central to the whole synthesis. Fluid precursors in the voids of crystal arrays can solidify by polymerization and sol-gel hydrolysis. More recently, many methods have been developed including salt precipitation and chemical conversion, chemical vapor deposition (CVD), spraying techniques (spray pyrolysis, ion spraying, and laser spraying), nanocrystal deposition and sintering, oxide and salt reduction, electrodeposition, and electroless deposition. 

Photoetching processes do not always consist of a simple superposition of an anodic and a cathodic partial process and may exhibit various types of complications. Firstly, even in the simple case of the photoetching of GaP single crystals in alkaline OBr solutions, the situation is actually more complex than depicted above, since at n-type crystals, it appears that the photoetching process itself induces a hole injection reaction and hence and electroless etching effect [24]. Initially, OBr is reduced at the GaP surface via the current-doubling mechanism (as is concluded from photocurrent measurements at p-type samples) ... 

Similarly to the kinetics of the electroless etching of GaP in alkaline Fe(CN)6 solutions, the kinetics of the chemical etching of [lll]-oriented GaP depend upon the crystal orientation whereas the etching rate at the (lll)-face is kinetically controlled, the etching rate at the (TTT)-face is diffusion-limited. This difference in reactivity of the GaP-face towards the electron acceptor Br2 is explained by the difference in the Ga-P surface dipole orientation [72]. 

Fig. 23. Rate of copper deposition, determined with a quartz crystal microbalance, vs. potential in an electroless copper plating bath at various formaldehyde concentrations. A 0 mmol dm HCHO, 15 mmol dm , 30 mmol dm , 45 mmol dm", O 60 mmol dm (B. J. Feldmann et al., 1989 [131]).

The three amplification procedures used with this functionahzed Au-quartz crystal interface consisted of detection first using avidin and biotin-labelled liposomes, secondly using avidin-Au-nanoparticle conjugate and the catalysed electroless deposition of gold, and thirdly avidin-alkaline phosphatase interaction with 5-bromo-4-chloro-3-indolyl phosphate causing the biocatalysed precipitation of the insoluble product on the piezoelectric crystal. The separation of surface treatment outside the QCM cell coupled with... 

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