Imaging X-ray fluorescence spectroscopy: laboratory measurements

Following on from the proof-of principle measurements of Martin et al. (X-ray Spectrom. 28 (1999) 64) we further describe the development of an imaging X-ray fluorescence (IXRF) spectrometer with no moving parts. Our laboratory system is based on a microchannel plate (MCP) “lens”, a CCD X-ray detector with good sub-keV quantum efficiency and a conventional electron bombardment X-ray source. We have used this equipment to form images of a standard XRF target, demonstrating that “elemental maps” (images of the target in the characteristic X-rays of one particular element) may be formed with sub-millimetre resolution. In addition to fluorescent X-rays, we detected X-rays which had been Bragg reflected from the polycrystalline aluminium substrate of the target. It is possible that the resulting “Bragg images” may be exploited to measure spatially varying strain, manifested as lattice distortion, introduced, for example, by thin films deposited on the surface of a sample.