In Situ Soft X-ray Spectroscopies Applied to Atmospheric Corrosion And Related Systems

Abstract: This thesis concerns the application of various soft x-ray spectroscopic methods (soft x-ray absorption, SXA, and emission, SXE) to complex, non-vacuum compatible systems, including liquids and multi-phase systems.The design, construction, and application of new instrumentation for in situ spectroscopy is described in detail. This includes sample holders using thin soft x-ray transparent membranes to enable measurements on systems completely isolated from vacuum, enabling flow of e.g. liquid or gas. In particular, a versatile setup for time resolved in situ chemical contrast x-ray transmission microscopy (CCXTM) was constructed and implemented. These instruments are expected to be applicable to a wide range of situations, for example in situ studies of chemical reactions, or biological specimen.The main project concerns atmospheric corrosion of iron in a saline environment, a process that requires the simultaneous presence of the solid (iron, NaCl), liquid (water) and gaseous (air) phases. It is also a highly inhomogeneous process, where lateral and time resolution is important. Using the CCXTM instrumentation, we were able to follow the distribution of all present elements over the sample with time resolution of a few minutes, and also to extract significant chemical information from the absorption edges. We observed e.g. the initial formation of corrosion products and transport of chlorine.Results from SXE measurements on water molecules in micelle structures are presented. A comparison with calculations reveal influence from the counter-ions, but also some spectral changes that may be attributed to water confinement.Also presented are angle dependent soft x-ray emission of liquid water, measuring scattered x-rays from different directions respect to the incident x-ray polarization. Existing preliminary theoretical expectations for the polarization dependence are contradictory. Our experiments show that a small angular anisotropy seems to be retained from the free molecule case.