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The development of X-ray photo-emission electron microscopy (XPEEM) for valence-state imaging of mineral intergrowths

A. D. Smith^1,*, P. F. Schofield^2,, G. Cressey², B. A. Cressey³ and P. D. Read⁴

¹ CLRC Daresbury Laboratory, Daresbury, Warrington WA4 4AD, UK
² Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
³ Science & Engineering Electron Microscopy Centre, Department of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK
⁴ CLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK

^* E-mail: adsmith{at}dl.ac.uk

We demonstrate the potential of X-ray photo-emission electron microscopy (XPEEM) to reveal valence-state images of the spatial distribution and relative concentration of metals in specific oxidation states. Additionally, XPEEM allows X-ray absorption spectra to be extracted from chosen pixel areas of the images. Using an in-house-built XPEEM instrument we show an application of the method in providing valence-state images of complex mineral intergrowths. The image resolution achieved with this instrument of simple design was ~5 µm and reasonable quality X-ray absorption spectra were extracted from areas of ~5 x 5 µm. These initial results suggest that by using commercial XPEEM instruments on 3^rd generation, high-brightness synchrotron sources a spatial resolution of 100 nm or better could be achieved, with the ability to extract high-quality X-ray absorption spectra from areas of 0.1 µm². Given that standard thin sections or polished blocks can be studied by XPEEM, and that each XPEEM image records ~1000 µm², XPEEM can be used in conjunction with other analytical methods such as EMPA and TEM-EELS/PEELS.

KEYWORDS: X-ray photo-emission electron microscopy, XPEEM, valence-state imaging, XAS, crystal chemistry

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