Montgomery has shown how SIMS depth profiling and focused ion beam imaging may be used to validate super- conducting test structures and to determine inter-diffusion between the layers in a multilayer structure. He used atomic force microscopy to assess the surface and beam induced topography, which were the factors limiting the ultimate resolution that could be attained [37]. Results of a depth profile of an YBCO/SrTiO3/MgO/YIG multi-layer are shown in Fig. 21. The analysis was achieved using a 15 keV oxygen primary ion beam and the layer thick- nesses corrected for their different sputter rates (which were measured in separate experiments). Montgomery also developed techniques for imaging the structure, us- ing the FIB system, and then reconstructing a ‘pseudo depth profile’ from the image data. This is an interest- ing and important approach when the sample is very rough.