Mossbauer surface imaging techniques

Several Mossbauer methods have been proposed to obtain spatially resolved information [33-35] but only a couple of them [36,37] make use of conversion electrons and can be considered as surface sensitive. 

6 RECENT SURFACE MOSSBAUER STUDIES IN AN ANCIENT MATERIAL Fe304 

More closely related to the aim of this chapter is the interest in the study of magnetite thin films. Apart from the possible applications of magnetite thin films in catalysis, magnetic recording media, or spintronic devices, many questions on their structural, magnetic, chemical, and electrical properties are still under discussion. 

In a subsequent paper, the same authors [40], by means of the deposition of ultrathin Fe304(00l) layers (0.4-2.4 nm) on Fe3 O4 (001) layers 20 nm thick, observed that the electronic structure of the surface layers of magnetite is strongly modified as compared to the bulk with a redistribution of the electronic char ge in the two or three outermost atomic layers. In particular, they observed that the intensity of the surface component associated with the Fe + octahedral ions was lower than the expected value either because the surface is rich in Fe + ions (due to vacancies in the octahedral sublattice) or because the electron hopping freezes at the outermost atomic layers. 

The authors would like to acknowledge the financial support from the Spanish Ministry of Science and Innovation under projects MAT2008-05763/NAN and MAT2009-I4578-C03-0I. 

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Apart from these four main techniques there are many other techniques but their applicability is often limited to some elements. MAS-NMR technique turns out to be very useful for determining if non zero nuclear spin elements are incorporated into the lattice because of its sensitivity to local environment symmetry. Also in favorable cases techniques as Mossbauer, diffuse reflectance UV-Vis and ESR spectroscopies are very helpful while high resolution electron micrographs and simulated imaging are of great interest (38) with in addition the possibility of specific chemical analysis at nanometer scale by EDX-STEM. At last XPS may be informative to determine if surface and bulk compositions are identical or not, although the technique by definition is only sensitive to the first top layers (1 to 2 nm) while zeolitic features concern the whole material. Some examples will be given below. 

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