Preliminary results from the development of a transmission x‐ray photoelectron spectrometer

Abstract

AbstractThere is an increasing demand to obtain XPS analyses from smaller sample areas. The development of a transmission x‐ray photoelectron spectrometer eventually will allow spectrum acquisition and imaging with a lateral resolution of 1 μm2. The principle is based on back‐foil excitation, originally described by Cazaux, where thin samples are placed on an aluminium anode. Electron irradiation of the anode produces a local source of x‐rays and thus a local source of photoelectrons from the opposite side of the sample.In this work a VG MA500 spectrometer was modified to give the 180° geometry for transmission x‐ray photoelectron spectroscopy. A hemispherical analyser with a high magnification lens replaced the cylindical mirror analyser of Cazaux's original work. The high magnification ensured a large solid angle of photoelectron collection and the hemispherical analyser gave the, previously unobtainable, energy resolution necessary to obtain chemical state information. Following Cazaux the aluminium anodes, either foils or evaporated directly onto the bulk side of the sample, were scanned by an electron beam. The maximum photoelectron lateral resolution obtainable is determined by the x‐ray excitation volume. This is reliant on the electron beam diameter, the accelerating voltage and the sample and anode thickness.We believe the local production of x‐rays by a scanning electron beam to be the ideal way of examining the microtomed sections through interfaces and soft composite materials. Hard materials require the use of ion beam thinning. Samples must be of submicrometre thickness (300 nm to 1 μm ideally).