Decomposition surfaces, SIMS studies

A combined XPS-SIMS study of dealuminated HFAU samples shows a significant gradient in the Si/Al ratio in the crystallites50. This gradient was ascribed both to a gradient of dealumination (i.e. dealumination is diffusion controlled) and to a selective deposit of silica on the outer surface of the crystallites. Silica was proposed to be formed from hydrolysis of SiF4 that results from the decomposition of hexafluorosilicate. 

The concept of intact emission of adsorbed molecular species for identifying reaction intermediates is also well illustrated in several recent studies. Benninghoven and coworkers (2-4,12) used SIMS to study the reactions of H2 with O2, C2H4 an< 2H2 on P°ly polycrystalline Ni. For the C2H /Ni interaction, for example, direct relationships could be established between characteristic secondary ions and the presence of specific surface complexes (12). In another study, Drechsler et al. (13) used SIMS to identify NH(ads) as the active intermediate during temperature-programmed decomposition of NH3 on Fe(110). 

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