DEVELOPMENT AND PRACTICAL APPLICATION OF A TRANSMISSION-X-RAY PHOTOELECTRON SPECTROMETER

There is an increasing demand to obtain XPS analyses from smaller samp le areas. The development of a transmission x-ray photoelectron spectr ometer will allow spectrum acquisition and imaging with a lateral reso lution of approaching 1 mum2. The principle is based on back-foil exci tation where thin samples were placed on an aluminium foil. Electron i rradiation of the foil produced x-rays locally and this, in turn, gave rise to a small source of photoelectrons from the opposite side of th e sample. Rastering the electron beam scanned the x-ray interaction vo lume, which allowed imaging. Photoelectron lateral resolution was depe ndent on the sample and foil thicknesses and was determined by the x-r ay excitation volume. In this work a VG Scientific MA500 was modified to give the ideal 180-degrees geometry for transmission x-ray photoele ctron spectroscopy (TXPS). A hemispherical analyser with an extended h igh-magnification transfer lens ensured a large solid angle of photoel ectron collection and the hemispherical analyser gave the, previously unobtainable, energy resolution necessary to obtain chemical state inf ormation. Certain aspects unique to TXPS and image interpretation are described, following discussions of spectral interpretation in the pre vious paper. It is believed that the local production of x-rays by a s canning electron beam is the ideal way to examine the ultramicrotomed sections through interfaces and soft composite materials. Harder mater ials, such as ceramics and metals, require ion beam thinning in a simi lar way to transmission electron microscopy specimens. A magnesium-alu minium alloy is ion beam thinned to demonstrate TXPS from a harder mat erial. The interlayer between a chlorine-containing latex and mild ste el is also analysed by TXPS following the removal of the bulk substrat e and ultramicrotomy. This illustrated the applications in adhesion sc ience, sample stability under analysis and localization of point analy ses.