Alloy films Auger electron spectroscopy

The characterization of evaporated alloy films can be carried out at widely different levels of sophistication. At the very least, it is necessary to determine the bulk composition, probably after the film has been used for an adsorption or catalytic experiment. Then various techniques can be applied, e.g., X-ray diffraction, electron diffraction, and electron microscopy, to investigate the homogeneity or morphology of the film. The measurement of surface area by chemisorption presents special problems compared with the pure metals. Finally, there is the question of the surface composition (as distinct from the bulk or overall composition), and a brief account is given of techniques such as Auger electron spectroscopy which might be applied to alloy films. 

It has indeed been found (83a) that the work function of Ag-Pd alloy films equilibrated at 300°C only changes from 4.38 eV at pure silver to 4.50 eV at 86% Pd (increasing to 5.22 at pure Pd). It was proposed (83a) that this work function pattern is a consequence of surface enrichment by silver and so confirmation of the theory awaits further work function measurements on alloy surfaces for which compositions have been determined by, say, Auger electron spectroscopy. 

There is now available a substantial amount of information on the principles and techniques involved in preparing evaporated alloy films suitable for adsorption or catalytic work, although some preparative methods, e.g., vapor quenching, used in other research fields have not yet been adopted. Alloy films have been characterized with respect to bulk properties, e.g., uniformity of composition, phase separation, crystallite orientation, and surface areas have been measured. Direct quantitative measurements of surface composition have not been made on alloy films prepared for catalytic studies, but techniques, e.g., Auger electron spectroscopy, are available. 

While the same basic mechanisms for passivity of pure metals also applies to alloys, the processes involved in the passivation of alloys have an added complexity. In many cases only one component of the alloy has the property of being passive in a particular environment. Alloys such as steiinless steels, which contain highly passive components (chromium in this case), owe their corrosion resistance to the surface enrichment of the passivating component Thus stainless steels resist corrosion in many acidic systems (where iron or carbon steel would be poorly passive or not passive at all) by a passivating oxide film containing Cr predominantly as Cr(III). Surface analytical techniques such as Auger electron and X-ray photoelectron spectroscopies reveal substantial enrichment of chromium in the passivating oxide film on these alloys " . There are only two ways by which this enrichment can... 

The paper by Watanabe et al. is important for alloy catalysis they examined the possible enrichment of Cu in the surface layers of Cu-Ni alloys. They used Auger spectroscopy to study the escape of low- and high-energy electrons (around 100 and 700-1000 eV) and were able to make quantitative in-depth profiles, of which an example is shown in Figure 2. This enrichment was also confirmed by AES measurements for films by Benndorf et al. ... 

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