Alloy films effects

This conclusion was additionally confirmed by Palczewska and Janko (67) in separate experiments, where under the same conditions nickel-copper alloy films rich in nickel (and nickel films as well) were transformed into their respective hydride phases, which were proved by X-ray diffraction. The additional argument in favor of the transformation of the metal film into hydride in the side-arm of the Smith-Linnett apparatus consists of the observed increase of the roughness factor ( 70%) of the film and the decrease of its crystallite size ( 30%) after coming back from low to high temperatures for desorbing hydrogen. The effect is quite similar to that observed by Scholten and Konvalinka (9) for their palladium catalyst samples undergoing the (a — j8) -phase transformation. 

It is particularly helpful that we can take the Cu-Ni system as an example of the use of successive deposition for preparing alloy films where a miscibility gap exists, and one component can diffuse readily, because this alloy system is also historically important in discussing catalysis by metals. The rate of migration of the copper atoms is much higher than that of the nickel atoms (there is a pronounced Kirkendall effect) and, with polycrystalline specimens, surface diffusion of copper over the nickel crystallites requires a lower activation energy than diffusion into the bulk of the crystallites. Hence, the following model was proposed for the location of the phases in Cu-Ni films (S3), prepared by annealing successively deposited layers at 200°C in vacuum, which was consistent with the experimental data on the work function. 

The structure of a vapor-quenched alloy may be either crystalline, in which the periodicity of the unit cell is repeated within the crystallites, or amorphous, in which there is no translational periodicity even over a distance of several lattice spacings. Mader (64) has given the following criteria for the formation of an amorphous structure the equilibrium diagram must show limited terminal solubilities of the two components, and a size difference of greater than 10% should exist between the component atoms. A ball model simulation experiment has been used to illustrate the effects of size difference and rate of deposition on the structure of quench-cooled alloy films (68). Concentrated alloys of Cu-Ag (35-65%... 

Fig. 26. Compensation effect plots for C2H, oxidation over Pd-Rh alloy films (O) and Pd-Ag alloy films (A) pure metals are indicated by solid symbols (73).

The Pt-Au films were not used in catalysis, but the chemisorption of CO was studied. The work function of Pt was only raised by 0.03 eV and there was no change with the alloys after short exposures to CO. It was therefore not possible to titrate the Pt content of the surface with CO in the same way as hydrogen was used with Cu-Ni alloy films (2). Long-term exposure of the films to 10 5-10-4 Torr CO at 20°C for periods up to four days caused the work function of the alloys to increase slowly Fig. 31. After 16 hr this increase was more evident in the Pt-rich region, but the effect was observed on the Au-rich regions after longer exposures. The effect was accelerated if the films were maintained at 100°C. These results were cited as direct evidence for the enrichment of the surface with platinum... 

In this chapter, the effect of preexcitation with the light of band-gap energy on trapping and thermal generation is examined in selenium and selenium-rich As-Se alloy films by several techniques. Results suggest that excess carrier trapping and dark-carrier generation are controlled by deep defect centers whose population can temporarily be altered by photoexcitation. 

Fig. 1 Side view of slab models of various bimetallic structures often used in computational studies. In each case, the bottom layers of the material are defined using the structure of a specified bulk material. The number of surface and bulk layers varies in different studies, (a) In the sandwich structure the surface is one component, often the same component as the bulk material and the second layer is another component. This structure is often used to determine ligand effects, (b) The pseudomorphic monolayer structure combines strain and ligand effects in one structure by placing a second component on top of a bulk material, (c) The near surface alloy combines strain, ligand and ensemble effects in one structure by considering an alloy film defined by just a few atomic layers on top of an ordered bulk material.

Fig. 16. Effect of NajW04, NH4Re04, and Na2Mo04 concentrations on the refractory metal (a) and phosphorus (b) content of electroless NiWP, NiReP, and NiMoP alloy films (T. Osaka et al., 1992 [38]).

The TCR value of an amorphous alloy strongly correlates with its specific resistance [49]. It also corresponds to the thermal effect on the specific resistance, i.e., the TCR increases at the temperature where the specific resistance abruptly decreases. The TCR values of alloys containing refractory metals exceed those of NiP NiReP alloy film annealed at 500°C in particular has an excellent TCR of 18 ppm K [36]. Although the TCR of as-plated crystalline NiMoP is lower than TCR values of amorphous alloys, heat treatment at 500 C slightly decreases the TCR to 134 ppm , which is a relatively high value, while the value measured after... 

Recent research on more coercive media with a low noise ratio involved addition of Zn to the Co alloy system [76-79]. Addition of Zn to the cobalt alloy very effectively produces a film with a fine particle structure, which results from codeposition of elements which are hardly soluble in the matrix. Such codeposition causes segregation and hence produces a film microstructure consisting of fine particles. The fine particulate structure lowers the noise ratio and increases the coercivity of the medium. 

The variations of vcol versus Es on the five nm-PtRu/GC electrodes are shown in Figure 16 [48]. The Stark shift for COl on all nm-PtRu/GC alloy film electrodes was measured to be around 34 cm V In contrast to the nm-Ru/GC electrode, where two Stark shift rates (a small value in the low potential region and a large value in the high potential region) were obtained, only one straight line can be drawn through the experimental data points. The results clearly demonstrate that the properties of an nm-PtRu/GC electrode are not a simple combination of the properties of nm-Pt/GC and those of nm-Ru/GC. The fact that the band center, the FWHM, and the Stark effect of the COl band all lie in between the values of nm-Pt/ GC and those of nm-Ru/GC confirmed that the alloy of PtRu thin film was formed by electrochemical co-deposition under cyclic voltammetric conditions. 

As shown in Fig. 9, the metal A is first plated or coated (by any process) on a substrate. Then the metal B is plated/coated on top of film A. Next a heat treatment is applied. If the melting temperature of metal A would be lower than that of metal B, the temperature should be slightly over the melting point of metal A. Then some of the metal A would melt, and the atoms of metal B would diffuse into the metal A at a very high speed, since one of the phases (phase of metal A) is a melted form. To enhance the antibacterial effect for tin plating used in food industries, tin was chosen as metal A. And as metal B, silver and copper were chosen independently. As a result, the process was used to produce tin-silver or tin-copper intermetallic compounds. The evaluation tests for the antibacterial effect (ISO 22196) confirmed that tin film did not show any antibacterial effect. On the other hand, the intermetallic compounds for the alloy films clearly showed antibacterial effects. This suggests that silver or copper could dissolve into the environment at a low concentration level, and that the silver or copper ions could make the antibacterial effect appear on materials surfaces. Fortunately, these well-known antibacterial metals could show antibacterial effects at very low levels [7]. 

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