Nickel oxide films monolayers

Formation of the first layer (a monolayer) of passivating oxide film on a denuded metal surface occurs very simply by the loss of protons from the adsorbed intermediate oxidation products, such intermediates being common to both dissolution and passivation processes . Thus for example, the first oxidative step in the anodic oxidation of nickel is the formation of the unstable adsorbed intermediate NiOH by... 

Consider the temperature. It is certainly known widely that heating in the presence of a corrosive gas produces bulk compounds on a surface, yet the critical temperature of surface compound formation is poorly known. Experiments of Mitchell and Allen (363) demonstrated that an oxide film 25 A thick forms by exposure of an evaporated copper film to oxygen at room temperature. When the temperature was lowered to — 183°C, however, only a monolayer was obtained. Evidently an oxidation temperature lies between these extremes. The experiments of Brennan and Graham (359) gave similar results for oxygen on nickel, and Koberts and Wells (364) have recently shown that oxygen penetrates aluminum films at — 195°C. 

In electronic applications, the corrosion of the surface leads to reduced performance and device lifetime. " In biomedical applications, corrosion leads to Ni ion release into the body and nickel toxicity. Therefore, forming an organic thin film on nickel oxide may serve as an effective barrier to conosioa This is in large part due to the flexibihty that SAMs offer they form stracturally well-defined films on the solid surface and they can be deposited by a nnmber of easy techniques such as immersing the substrate in solution, aerosol spraying and vapour deposition. Currently, immersion coating is the most popular and widely studied method for monolayer formation. " ... 

Passivity has been attributed, since the time of Faraday, to an oxide film. In a few cases the presence of this has been directly demonstrated, and the response of a passive electrode to pH changes is very much that of a metal-metal oxide electrode. Uncertainties still exist, however, as to the nature and thickness of the surface film. On platinum, nickel and iron the onset of passivation may only require a monolayer of oxide, or of adsorbed oxygen atoms, although a layer several Angstroms thick may be produced in time. Evidence for these very thin layers, which are quite undetectable visibly, comes from the very small cathodic pulse of electricity that is sufficient to remove them. In other cases, e.g. lead, quite thick films are needed to preserve the passive state. Partial protection is obtained for many metals in a variety of electrolytes so long as conditions favour the precipitation of a film of insoluble hydroxide or salt (see Anodising),... 

Dell and Stone 5) have already discussed this mechanism in their study of the chemisorption of oxygen on oxide-coated nickel powders. These workers found that only a monolayer of oxide formed during activation which followed oxygen chemisorption at 25° in the film thickness range from about 25 to 110 A. This behavior might be expected also with cobalt, although here the film thickness at which this mechanism alone operates is certainly greater than 25 A. 

The various versions of inverse photoemission have been applied to purely basic problems, just as with UPS and ELS. Recent typical examples include the bonding of Hj on Ni (110) 3I4J the oxidation of a titanium thin film [315] the effects on Ht chemisorption of a monolayer of nickel on Cu (111) [316] unoccupied electronic structure in La2Cu04 [317] and in Bi2Sr2CaCu20g [318] and KRIPES studies of the Ge (113) (2x1) [319] and TiNo.8.1 (100) [320] surfaces. 

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