Valence state map of iron oxide thin film obtained from electron spectroscopy imaging series

Abstract

This paper demonstrates the applicability of electron-spectroscopic imaging (ESI) for valence-state mapping of the iron oxide system. We have previously developed a set of signal-processing methods for an EST series, to allow mapping Of sp(2)/sp(3) ratio, dielectric function and energy bandgap. In this study, these methods are applied to generate a valence-state map of an iron oxide thin film (Fe/alpha-Fe2O3). Two problems, data undersampling and a convolution effect associated with extraction of the image-spectrum from the core loss image series, were overcome by using cubic-polynomial interpolation and maximum-entropy deconvolution. As a result, the reconstructed image-spectrum obtained from the EST series images has a quality as good as that of conventional electron energy-loss spectra. The L-3/L-2 ratio of the reconstructed EST spectrum is determined to be 3.30 +/- 0.30 and 5.0 +/- 0.30 for Fe and alpha-Fe2O3, respectively. Our L-3/L-2, ratio mapping shows an accurate correspondence across the Cu/Fe/alpha-Fe2O3 region. The effect of delocalization and chromatic aberration on the EST resolution is discussed and estimated to be about 2 nm for the case of L-3/L-2, ratio mapping. (c) 2006 Published by Elsevier Ltd.