Nickel-iron thin films

It is to note that the theoretical approach to the problems of deposit orientation was successfully developed by Pangarov et al. [21,49,50]. Using this theory, it was possible to determine the preferred orientation as a function of overpotential from silver single crystals [50] to nickel and iron thin films [21, 50]. 

Electroless reactions must be autocatalytic. Some metals are autocatalytic, such as iron, in electroless nickel. The initial deposition site on other surfaces serves as a catalyst, usually palladium on noncatalytic metals or a palladium—tin mixture on dielectrics, which is a good hydrogenation catalyst (20,21). The catalyst is quickly covered by a monolayer of electroless metal film which as a fresh, continuously renewed clean metal surface continues to function as a dehydrogenation catalyst. Silver is a borderline material, being so weakly catalytic that only very thin films form unless the surface is repeatedly cataly2ed newly developed baths are truly autocatalytic (22). In contrast, electroless copper is relatively easy to maintain in an active state commercial film thicknesses vary from <0.25 to 35 p.m or more. 

The current-potential relationship ABCDE, as obtained potentiosta-tically, has allowed a study of the passive phenomena in greater detail and the operational definition of the passive state with greater preciseness. Bonhoeffer, Vetter and many others have made extensive potentiostatic studies of iron which indicate that the metal has a thin film, composed of one or more oxides of iron, on its surface when in the passive state . Similar studies have been made with stainless steel, nickel, chromium and other metals... 

A novel polysiloxane, containing the isocyanide group pendent to the backbone, has been synthesized. It is observed to react with the metal vapors of chromium, iron and nickel to afford binary metal complexes of the type M(CN-[P])n, where n = 6, 5, 4 respectively, in which the polymer-attached isocyanide group provides the stabilization for the metal center. The product obtained from the reaction with Fe was found to be photosensitive yielding the Fe2(CN-[P])q species and extensive cross-linking of the polymer. The Cr and Ni products were able to be oxidized on exposure of thin films to the air, or electrochemically in the presence of an electron relay. The availability of different oxidation states for the metals in these new materials gives hope that novel redox-active polymers may be accessible. 

Singh R.N., Pandey J.P., Anitha K.L., Preparation of electrodeposited thin films of nickel-iron alloys on mild steel for alkaline water electrolysis. Part I Studies on oxygen evolution, Int. J. Hydrogen Energ., 18(6), 467-473,1993. 

Thin films of a composite nickel-iron (9 1 Ni/Fe ratio) and iron-free oxyhydroxides were deposited from metal nitrate solutions onto Ni foils by electroprecipitation at constant current density. A comparison of the cyclic voltammetry of such films in 1M KOH at room temperature (see Fig. 6) shows that the incorporation of iron in the lattice shifts the potentials associated formally with the Ni00H/Ni(0H)2 redox processes towards negative potentials, and decreases considerably the onset potential for oxygen evolution. The oxidation peak, as shown in the voltammo-gram, is much larger than the reduction counterpart, providing evidence that within the time scale of the cyclic voltammetry, a fraction of the nickel sites remains in the oxidized state at potentials more negative than the reduction peak. 

The transition from the active state to the passive state is the passivation, and the transition in the reverse direction is the activation or depassivation. The threshold of potential between the active and the passive states is called the passivation potential or the passivation-depassivation potential. Similarly, the transition from the passive state to the transpassive state is the transpassivation, and the critical potential for the transpassivation is called the transpassivation potential. Further, a superficial thin film formed on metals in the passive state is often called the passive film (or passivation film), the thickness of which is in the order of 1 to 5 nm on transition metals such as iron and nickel. 

Magnetic thin films of nickel-iron (usually deposited at an 80 20 composition by weight) exhibit a number of unusual properties, which have led to many experimental and theoretical studies, as well as to impoitant applications in binary storage and switching, magnetic amplifiers, and magneto-optical Kerr-effect displays,... 

Objects of iron are often nickel-plated, or covered with a thin film of nickel, a white, hard metal which preserves its lustre in air, for it is not easily oxidisable. This is done by making the object to be coated with nickel the kathode and a bar of nickel the anode the liquid is a solution of oxalate of nickel and potassium. Iron objects are first coated with copper before nickelling. Silver and gold are best deposited from their double cyanides with potassium these salts are used because the deposit is harder and more uniform than if a halide be used. In thus coating objects, it is of importance that the current density, i.e. the ratio of the current to the area of the surface of the object to be coated, should be considered if this be too high, the metal will be deposited in a loose, flocculent condition. 

Thin films of widely variable composition (mainly rare earth oxides, nickel, iron and other metal oxides, but also other simple and complex compounds) have been used for a variety of purposes (namely in semiconductor technology, optical and electronic applications... 

G.T. Stauf, D.C. Driscoll, P.A. Dowben, S. Barfuss, and M. Grade, Iron and Nickel Thin Film Deposition via Metallocene Decomposition, Thin Solid Films, Vol.153, 1987, pp.421-430. 

Marin IVL, Ortuno M, Hernandez A, Abelian J (1990) Peicolative treatment of the Verwey transition in cobalt-iron and nickel-iron ferrites. Physica Status Solidi (B) 157 275-280 McElhiimy MW, McFadden PL (1999) Paleomagnetism. Academic Press, New York McVitie S, Chapman JN (1995) Coherent Lorentz imaging of soft thin-film magnetic materials. Mater Res Soc Bull, October 1995 55-58... 

The principal use of the carbonyls is that of obtaining pure metals. The Mond process for refining nickel and the preparation of pure iron for special pui oses, such as magnet cores, involve the formation of a volatile carbonyl, transport of the vapors away from impurities in the original metal, and subsequent decomposition to obtain the pure metal. The carbonyls of chromium, molybdenum, and timgsten have been used in mass spectroscopy to determine the stable isotopes of the respective metals. Nickel carbonyl has been used to obtain metallic mirrors and to coat objects with a thin film of metal. Iron carbonyl has been used as an antiknock agent in gasoline. 

Secondary fluorescence or second element effects. In circumstances where the energy of a fluorescence photon (e.g., nickel K-L23 at 7.47 keV) lies immediately above the absorption edge of a second element (e.g., iron K-line edge at 7.11 keV) (Figure 4), the fluorescence intensity of the second element (iron K-L2,3) will be enhanced due to preferential excitation by fluorescence radiation (i.e., nickel K-L2,3) within the sample. The magnitude of this effect is not always significant except for certain combinations of elements in alloys (e.g., iron-chronium-nickel) and in multilayer thin films. 

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