Surface compositional changes techniques

LEIS is not normally used solely as a means of determining surface compositions. The technique is mainly exploited in cases where it is desirable to be able to follow changes in the outermost surface layer of the sample as a function of time, or of some kind of process. An elegant use of the technique is as a highly sensitive monitor of compositional changes during ion beam depth profiling, with the same beam in use for sample erosion and LEIS measurements. 

The simplest technique introduced by Young as early as 1805 [18] is the measurement of the contact angle as a measure of surface tension and surface energy [1,19, 20,21], In many cases this gives an indication of surface composition and can be used to observe changes in composition, structure and/or roughness at the surface during a particular surface treatment. A quantitative description or distinction between different parameters is hardly possible in most cases. 

The information contained in ESCA (Electron Spectroscopy for Chemical Analysis) spectra [331] makes the method particularly suitable for determinations of surface compositions, chemical bonding of surface atoms and changes which occur at solid surfaces during reaction [312], Applications of this technique to the study of reactions of and between solids are awaited with interest. 

Motivating the research is the need for systematic, quantitative information about how different surfaces and solvents affect the structure, orientation, and reactivity of adsorbed solutes. In particular, the question of how the anisotropy imposed by surfaces alters solvent-solute interactions from their bulk solution limit will be explored. Answers to this question promise to affect our understanding of broad classes of interfacial phenomena including electron transfer, molecular recognition, and macromolecular self assembly. By combining surface sensitive, nonlinear optical techniques with methods developed for bulk solution studies, experiments will examine how the interfacial environment experienced by a solute changes as a function of solvent properties and surface composition. 

Surface-to-subsurface migrations in bimetallic NPs can completely change the surface composition and drastically alter catalytic performance. Despite the importance of atomic mobility in bimetallic systems, little is known about the dynamic processes of NPs and clusters due, in large part, to the lack of suitable experimental techniques. 

In recent years, AES (2), ultraviolet photoelectron spectroscopy (20), and X-ray photoelectron spectroscopy (21a) have come to play prominent roles in studies analyzing the composition and bonding at surfaces. These techniques can conveniently be used to determine nondestructively the composition of the surface and changes of the surface composition under a variety of experimental conditions. Since the Auger transition probabilities are large, especially for elements of low atomic number, surface impurities in quantities as little as 1% of a monolayer ( 1013 atoms/cm2) may be detected. 

Are there potential problems in the use of the selected techniques Do the experimental requirements of the technique and the appropriate corrosion conditions combine to give information that is not altered by sample handling or the measurement process itself Is the sample stable under vacuum Is the chemistry or surface composition altered by electron, ion or X-ray beam excitation Does the corrosion layer change upon cooling or removal from solution ... 

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