Charge exchange, alloys

The yield equation modified for charge exchange in LEIS is given in Eq. (3.3.18). is the probability that the ions leaving the surface are in a charged state. To overcome this uncertainty in practical analysis, the most reliable approach is to use standards [4, 5]. Thus to measure the composition of the surface layer of an alloy (PtNi) or of Pt deposited on an Rh surface, the yields from dean elemental surfaces can be obtained and related to the number of atoms on the modified surface. Using these standards, it is possible to measure the concentration of two or more elements on a surface. Consider the case of a surface composed of elements a and b. On the pure standard surface in each case... 

Electrochemical Properties All C Vs are presented on two different scales to show both the larger and smaller peaks in sufficient detail. At low Pt surface concentrations, the base CVs are very similar to those of the Pt island-modified Ru(OOOl) surfaces (see Fig. 14.5). With increasing Pt surface content, however, the charge in the Hupmore than one Ru atom were required for OHad and/or Hupd adsorption. Since the atom distribution in PcRui a /Ru(0001) surface alloys is very close to a random distribution [Hoster et al., 2008], the number of Ru sites is proportional to xj/u or (1 — xpt)". As is evident from the plot in Fig. 14.6, the experimental data agree very... 

The conclusions arrived at in the photoemission studies described above are in agreement with similar conclusions reached by Azoulay and Ley (1979) for crystalline Gd-Fe compounds. The photoemission results do not reveal major differences in electronic structure between crystalline and amorphous alloys of similar composition, but they make it clear that the reduction in 3d moment in both classes of materials is mainly due to a reduction in 3d band exchange splitting. In conclusion, charge transfer does occur upon alloying but it is too small to account for the changes in 3d moment observed. 

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