MONITORING PARTICLE-SIZE CHANGES OF A SUPPORTED PHASE BY ESCA

Fe 2p is the preferred ESCA photoelectron peak to analyze iron species with an Al K-alpha anode, but it has proved difficult to use in quantitative measurements because of the large inelastic background generally associated with it. The Fe 3p photoelectron peak lends itself to a more accurate estimate of the iron intensity, but does not provide qualitative features sufficient to differentiate iron species. It is shown that by use of results obtained for the Fe 3p/Al 2p intensity ratio relative to the value predicted for monolayer dispersion, the optimum Fe 2p peak integration limits and background substraction method may be obtained. The Fe 2p3/2 partial area, obtained by subtracting an integral background, provides the most accurate measurement of the Fe 2p intensity. This allows the intensity of the Fe 2p3/2 peak to be compared to both the intensity of the Fe 3p photoelectron peak and the magnitude of the inelastic electron background. These two measures yield information about the mean particle size of the supported iron phase. Both methods are most responsive to variations in the mean particle size less than three times the inelastic mean free path of the measured photoelectron.