Simultaneous deposition of metals

Codeposition (electrochemical) — Simultaneous deposition of metals, or of a compound as a result of at least two simultaneously proceeding reactions. Thus the codeposition of copper and selenium as Cu2Se results when a solution containing Se(IV) and Cu(II) is reduced at a suitable potential. Codepositions are used for the electrochemical synthesis of -> semiconductors, and of... 

Fig. 27 The simultaneous deposition of metals Mi and M2 in which the rest (equilibrium) potential Erj is more positive than Er 2 ar d = a2-...

The cryochemical method allows the preparation of both homometallic and het-erometallic polymer-immobihzed cluster particles. Thus the consecutive or simultaneous deposition of metal vapors of different elements (e.g., Mo and Ti or Ti and Cr), especially at high concentrations, yields the nonsolvated bimetallic clusters These clusters are close in size to the colloidal particles (Cr -Ti ) (scheme 6) or to small clusters. For example, cluster Mo Ti includes 13 atoms. 

Miscellaneous. Electron beams can be used to decompose a gas such as silver chloride and simultaneously deposit silver metal. An older technique is the thermal decomposition of volatile and extremely toxic gases such as nickel carbonyl [13463-39-3] Ni(CO)4, to form dense deposits or dendritic coatings by modification of coating parameters. 

Of recent years the use of mercury film electrodes based on substrates other than platinum has been explored, and increased sensitivity is claimed for electrodes based on wax-impregnated graphite, on carbon paste and on vitreous carbon a technique of simultaneous deposition of mercury and of the metals to be determined has also been developed. 

Fu, Y. and Zang, L. (2005) Simultaneous deposition of Ni nanoparticles and wires on a tubular halloysite template A novel metallized ceramic microstructure. Journal of Solid State Chemistry, 178, 3595-3600. 

The deposition of metals has also been studied by a large number of electrochemical techniques. For the deposition of Cu2+, for example, it is reasonable to ask whether both electrons are transported essentially simultaneously or whether an intermediate such as Cu+ is formed in solution. Such questions, like those of the ECE problem discussed above, have usually been investigated by forced convection techniques, since the rate of flow of reactant to and away from the electrode surface gives us an important additional kinetic handle. In addition, by using a second separate electrode placed downstream from the main working electrode, reasonably long-lived intermediates can be transported by the convection flow of the electrolyte to this second electrode and detected electrochemically. 

To express the preceding in a different, more specific way, we state that codeposition of two or more metals is possible under suitable conditions of potential and polarization. The necessary condition for simultaneous deposition of two or more metals is that the cathode potential-current density curves (polarization curves) be similar and close together. 

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... 

This chapter concerns composite films prepared by physical vapor deposition (PVD) method. These films consist of dielectric matrix containing metal or semiconductor (M/SC) nanoparticles. The structure of films is considered depending on their formation by deposition of M/SC onto dielectric substrates as well as by layer-by-layer or simultaneous deposition of M/SC and dielectric vapor. Data on mean size, size distribution, and arrangement of M/SC nanoparticles in so obtained different composite films are given and discussed in relation to M/SC nature and matrix properties. Some models of nucleation and growth of M/SC nanoparticles by the diffusion of M/SC atoms/molecules over a surface or in volume of dielectric matrix are proposed and analyzed in connection with experimental data. 

Simultaneous evaporation of metal with organic and inorganic substances followed by vapor deposition on a substrate allows the production of composite films containing M nanoparticles stabilized in various dielectric matrices [2, 28]. The use of monomer molecules in this process polymerizing during deposition or as a result of the subsequent reactions yields polymeric nanocomposite films with metal inclusions [2, 3, 28, 37]. The new low-temperature synthesis of polymeric nanocomposite films has been elaborated recently. This synthesis is based on the deposition of M/SC and monomers vapors at temperature 80 K followed by low-temperature solid-state polymerization of obtained films in conditions of frozen thermal movement of molecules (cryochemical synthesis) [2], This synthesis has important features, which will be considered further. 

Should there be no interaction of the deposited metals (i. e. should no alloy be formed), a simultaneous deposition of different metals is possible only when their deposition potentials are equal. As these deposition potentials are determined by the sum of reversible (reduction) potentials and of the corresponding overvoltage value [Pg.151]

In cases where the difference in the standard potential is not so great, both curves can be made to run closer or farther apart by a suitable choice of reaction conditions lhus tho simultaneous deposition of both cations can be either facilitated or made more difficult. It is possible, for example, to carry out a simultaneous cathodic deposition of tin and lead from the solution of their chlorides it only requires a suitable adjustment of respective concentrations of their salts in the solution because tho standard potentials of both these metals are very near to each other (nSn — —0.14, tcpi, — —0.13). If an acid solution is used hydrogen ions should be discharged theoretically prior to both metals (tc h2 = 0), yet in fact, tho hydrogen overvoltage at both metals is so high that no hydrogen will be evolved at all. 

The distance between the current curves of two metals may sometimes be controlled by temperature as the value of the overvoltage varies under its effect. The depositi m potentials of nickel and zinc on electrolysis of their salts in aqueous ammonia solution at 20 °C differ only slightly because the high overvoltage for nickel reduces the difference between the respective reversible potentials, thus making simultaneous deposition of both metals quite possible. On the other hand overvoltage for nickel at 90 °C is considerably lower so that the difference between the deposition potentials increases and simultaneous deposition of nickel and zinc is no l nger possible. 

However, the reason of the appearance of negative impedance is always a chemical/electrochemical process. In most cases the blocking (inactivation) of the electrode (metal) surface is the pivotal (autoinhibition) step in the mechanism behind the emergence of the oscillating behavior. The blocking can be a consequence of adsorption of ions or molecules, chemisorption of molecular fragments, deposition of metals, salts or other compounds, formation of oxide layer etc. In all cases several coupled, consecutive, and simultaneous processes occur. The oscillating behavior appears only at a certain set of parameters (concentrations of the electro-chemically active species, the nature and the concen-... 

The electrolytes contain approximately 1 g. atom per liter of the corresponding metal in each case. It is evident that whereas simultaneous deposition of copper, cadmium and zinc is improbable from the solutions containing the simple ions, it should, and in fact does, occur from the complex cyanide solutions. 

Depolarization of metal deposition sometimes occurs when two metals which separate simultaneously form compounds or solid solutions. The reversible potential of a solid solution generally lies in between those of the pure constituents hence an alloy containing both metals may be deposited at a potential that is less cathodic than that necessary for the less noble constituent in the pure state. This probably accounts for the fact that zinc and nickel are deposited simultaneously at a potential of about — 0.6 volt, whereas that required for pure zinc is nearly 0.2 volt more cathodic. The simultaneous deposition of the iron-group metals is partly due to the similarity of the discharge potentials, but the formation of solid solutions also plays an important part. Although the deposition potentials of cobalt and nickel are lower than that of iron, the cathodic deposit almost invariably contains relatively more of the latter metal. ... 

Separation of Metals by Electrolysis.—The complete separation of one metal from another is important in quantitative electro-analysis the circumstances in which such separation is possible can be readily understood from the preceding discussion of simultaneous deposition of two metals. The conditions must be adjusted so that the discharge potentials of the various cations in the solution are appreciably different. If the standard potentials differ sufficiently and there are no considerable deposition overvoltages, complete separation within the limits of analytical accuracy is possible this is, of course, contingent upon the metals not forming compounds or solid solutions under the conditions of deposition. Since the concentration of the ions of a deposited metal decreases during electrolysis, the deposition potential becomes steadily more cathodic, and may eventually approach that for the deposition of another metal. For example, if the ionic concentration is reduced to 0.1 per cent of its original value, the potential becomes 3 X 0.0295 volt more cathodic for a bivalent metal and 3 X 0.059 volt for a univalent metal, at ordinary... 

There is a significant difference between copolymerization and codeposition. An example of codeposition is the simultaneous deposition of parylene or a plasma polymer and an evaporated metal, in which each component can be deposited regardless of whether or not the other component is being deposited. Plasma polymerization of a mixture of two hydrocarbons, e.g., CH4 and C2H4, is essentially codeposition of the respective plasma polymers. In contrast, plasma polymerization of gases occurs only in the presence of polymer-forming plasma. This is similar to the copolymerization of maleic anhydride, which does not polymerize, with other vinyl monomers. 

In selected cases two different metals can be codeposited onto a substrate by electroless plating. Shu etal. [1993] have attempted simultaneous deposition of palladium and silver... 

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