"Total" Ion Beam Analysis – 3D imaging of complex samples using MeV ion beams

In this Chapter the synergy between a number of closely related techniques for thin film depth profiling are described; they all use ion beams from MV accelerators as probes. These include the nuclear methods: RBS, EBS, ERD, NRA (and see PARTICLE SCATTERING in the COMMON METHODS Chapter). But they can also include PIXE (see ATOMIC EXCITATIONS in the COMMON METHODS Chapter). See Table 1 for the expansion of the acronyms and references to the list of the detailed articles on individual techniques: this article will not describe the techniques themselves but will concentrate specifically on the synergisms available. I will use acronyms for complementary techniques freely: a Glossary for these can be found in the INTRODUCTION to this Chapter (ION BEAM METHODS). "Total IBA" is operating when multiple IBA techniques are being handled self-consistently to obtain more information than the sum of that available from each technique handled separately [ ]. We will show that the sum of the whole is far more than the sum of the parts, to the extent that new classes of samples become tractable and new types of characterisation become feasible: the various IBA techniques are in fact strongly complementary. Indeed, we believe that chemical tomography is feasible with these new techniques. The alert reader will object that we are only stating the obvious here: it is easy to find examples showing that this complementarity has always been recognised. For example, Feldman et al presented a paper combining He-RBS and He-PIXE to the first Ion Beam Analysis Conference nearly forty years ago in 1973 [ ]. The Abstract (not available electronically) is informative for us :- Anodic oxide films on GaAs have been studied by the combined use of He back-scattering [sic] and He-induced X-rays. Back-scattering is hampered by the lack of mass resolution between Ga and As. X-ray analysis has excellent mass resolution but poor depth resolution. This poor depth resolution is overcome by increasing the effective thickness of the films by entering at grazing angles and making use of the property that the He-induced X-ray cross-sections fall steeply with decreasing energy. This technique and the methods of data analysis are discussed in detail. The anodic oxide films are found to be deficient in As within 200Å of the surface and to have a Ga:As ratio of approximately 1:1 for the rest of the oxide. On heating to 650°C most of the As diffuses out of the films. This early use of RBS/PIXE is exemplary, and includes an explicit awareness of the strengths and weaknesses of each technique. We shall underline these below, and show why it is only recently that the idea of using the IBA techniques self-consistently has been picked up and made usable by the analytical community