Instrumental effects in quantitative Auger electron spectroscopy

Abstract

Experiments used to determine the energy resolution, field of view, depth of field and instrumental response of a concentric hemispherical analyser (CHA) are described. The effect of analysis energy on the size and shape of the field of view is investigated using a procedure which employs the imaging facilities of a scanning Auger electron microscope. The transmission of the CHA, for different input lens retardation ratios, is found, firstly, in an experiment using a thermionic electron source and, secondly, using the departure from linearity of spectra plotted in a log N ( E) vs log E form. Such a plot is found to provide a convenient and sensitive method of detecting possible sources of error, such as mispositioning of the sample surface or electrostatic charging of material in the specimen region. These findings indicate the need for careful mechanical alignment of the spectrometer and for the sample surface to be positioned reproducibly within ±200 μm of the centre of the CHA field of view to ensure an accuracy of better than ±10% in estimates of Auger current. A procedure for repositioning the specimen to give a reproducibility of ca +2% in signal measurement is deduced. Computer techniques, to correct for effects of both spectrometer transmission and detector efficiency, are described.