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Erosion and subsequent re-deposition, mixing of materials and in particular the trapping of hydrogen isotopes in deposited layers at surfaces is of great concern in large fusion experiments. Ion micro beam analysis has been applied to the investigation of plasma deposited layers covering the divertor tiles in the JET tokamak. The layers, 50-150 m thick they are not easily accessible by conventional ion beam analysis methods, but cross sections can be prepared by cutting and polishing and then analysed. An ion microbeam setup is presented which makes it possible to do elemental analysis with about 5 m spatial resolution. A combination of analysis methods is presented which allows accurately calibrated and sensitive measurements of beryllium, oxygen, deuterium and stainless steel components in carbon matrix. In particular the report addresses a number of specific analysis difficulties, such as the influence of polishing and sample handling on the beryllium and oxygen content at the polished surfaces and the de-trapping and thermal release of hydrogen during ion beam irradiation at high current densities.
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