Wall Forum 2017

The elemental mapping of large areas using ion beam techniques is a desirable capability of several scientific communities, involved on topics ranging from geoscience to cultural heritage. Usually, the constraints for large-area mapping are not met in setups employing micro- and nano-probes implemented all over the world. In this sense, a novel setup for mapping large sized samples in an external beam was recently built at the University of São Paulo employing a broad MeV-proton probe with sub-millimeter dimension, coupled to a high-precision large range XYZ robotic stage (60 cm range in all axis and precision of 5 um ensured by optical sensors). An important issue on large area mapping is how to deal with the irregularities of the sample's surface, that may introduce artifacts in the images due to the variation of the measuring conditions. In our setup, we implemented an automatic system based on machine vision to correct the position of the sample to compensate for its surface irregularities. As an additional benefit, a 3D digital reconstruction of the scanned surface is also obtained. [mehr]

With the well-succeeded commissioning of the ToF-RBS, we performed a series of experiments aiming new insights on the variation of the surface composition of Tungsten-containing steel alloys due to the preferential sputtering induced by low energy Deuterium irradiation. We exposed W-Fe models systems with three different Tungsten concentrations and EUROFER to a Deuterium beam with 200 eV energy at fluences of 10^23 D/m^2. The ToF-RBS with a 2.0 MeV Silicon ion beam achieved enough depth-resolution to reveal the resulting profiles after irradiation. The combination of the ToF-RBS data with ToF-ERD data, together with surface morphology information obtained by AFM, provided an improved computational modeling of the samples using the MultiSIMNRA software. The profiles revealed that the light elements present in the near-surface regions, i.e. Oxygen and Carbon, may play some hole of importance either in the dynamics of the process (considering the presence of these elements prior the irradiation) or in the interpretation of the results (considering the incorporation of these elements after the exposure). The obtained profiles are in good agreement with the ones obtained by XPS, with the advantage of a direct assessment of the W-profiles with no need for corrections. The analysis of samples irradiated at a high temperature indicates a different behavior for the EUROFER when compared to the model systems, possibly due to Tungsten segregation that occurs in the latter. SEM-EDX measurements confirm segregation on model systems and not on EUROFER. [mehr]