X-ray excited optical luminescence (XEOL) refers to the trans-visible emission produced as a consequence of X-ray bombardment and provides an alternative detection method for X-ray absorption spectroscopy (XAS). Whereas XAS measured by conventional means (absorption, X-ray fluorescence) generally yields spectra characteristic of the bulk, the shallow escape depth of visible photons provides surface specificity of ~ 200 nm. Combining this with the relative ease of manipulating the emission using conventional optics gives us the basis for a method of mapping surface chemical states on the micron scale — XEOL microscopy (XEOM). As part of an ongoing project looking into the use of XEOL to study the chemical systems relevant to the corrosion of heritage artefacts, a portable XEOM instrument, XEOM1, has been constructed. Here, a detailed account of the development process is given, including descriptions of the microscope itself (optics, detectors, auxiliary hardware) and of its support system (control electronics and software). Data processing challenges are also discussed. Testing of XEOM1 has involved deployment on multiple synchrotron beamlines and data acquired from samples comprising of corroded copper surfaces (coupons, meshes) are presented in order to demonstrate how XEOM1 can be used for surface chemical analysis. XEOL spectra have been obtained by acquiring image 'stacks' — each stack is sequence of images resolved in energy across an absorption edge — and extracting data from regions of interest (ROIs) in each image. Chemical identification is achieved through analysis of the nearedge structure (XANES). Subtraction of pre- and post-edge images also gives a method for fast elemental mapping. Several options for future development of the XEOM1 hardware and related investigations are also proposed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:606206 |
| Date | January 2014 |
| Creators | Hand, Matthew |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/61954/ |
Page generated in 0.1368 seconds