Surface structure impinged

Either a photon or an electron impinges on the surface. This photon or electron may be polarized to yield additional surface information. The electron, part of a well-collimated and monoenergetic electron beam, may be multiply scattered by surface atoms before reaching step 2. Multiple scattering is most marked at kinetic energies below about 200 eV and can make the process particularly sensitive to the surface structure at these lower energies. 

Besides crystal planes parallel to the surface, further planes exist that might reflect impinging X-rays. The scattered X-rays are not in the plane of reflection and are called off-specular reflections. Their intensity is also high at the Bragg angles. As with the specularly reflected X-rays, the weak signal between these peak intensities contains surface-relevant information. A combined analysis of these reflections often leads to a complete picture of the surface structure. 

In a MEIS experiment, a collimated beam of monoenergetic protons or He-ions impinges onto a crystalline target along a known crystallographic direction. The energy and angle of the scattered ions are analyzed simultaneously and allow MEIS to measure atomic mass, depth, and surface structure. 

Macroscopic heterogeneities, e.g. crevices, discontinuities in surface films, bimetallic contacts etc. will have a pronounced effect on the location and the kinetics of the corrosion reaction and are considered in various sections throughout this work. Practical environments are shown schematically in Fig. 1.3, which also serves to emphasise the relationship between the detailed structure of the metal, the environment, and external factors such as stress, fatigue, velocity, impingement, etc. 

Surface preparation is of prime importance, and optimum performance of modern protection coatings can be achieved only if the surface of the steel has been adequately treated. The method of surface preparation depends on the shape and size of the structure or component. Thus it is preferable to blast-clean an openwork steel structure by manual methods, since with this type of structure automatic blast cleaning would lead to excessive impingement of the abrasive on the machine itself. 

A number of surface diffraction techniques can be employed in the structural study of electrochemical interfaces, depending on the details of the system under study. For bulk materials or thick films (such that the X-ray beam only samples that layer) conventional diffraction experiments can be performed and, in fact, a number of in situ X-ray diffraction studies of this type have been reported.126 129 In the case of thin films or monolayers, two different techniques can be employed and these are the reflection-diffraction technique introduced by Marra and Eisenberger,3 ), 32 and the technique based on surface truncation rods.131 In the first case, the incident X-ray beam impinges on the sample at an angle below... 

Very thin films exhibit special structure because of their confined geometry between substrate and surface. Their structure cannot be studied in a normal setup. In order to obtain enough photons on the detector, the X-ray beam must impinge on them under grazing incidence (Cf. Sects. 7.6.3.1,1.63.2, 8.8). This technique is suitably combined with microbeams. Current effort is focusing both on progress of the instrumentation and on the development of adapted analysis methods. 

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