An experimental approach to the determination of the surface ionization φ(0) in electron probe microanalysis

A compilation of experimentally determined surface ionization values for Al Kα and Pd Lα radiation on a wide variety of substrates, ranging from beryllium to bismuth, and measured between 4 and 30 kV, is presented. The values were extracted from our previously reported thin‐film measurements on aluminum and palladium films by electron probe microanalysis. The φ(0) values were determined by establishing the ratios of the intensities emitted from the supported and unsupported films for six film thicknesses and extrapolating towards a film thickness approaching zero. Some 180 φ(0) data each for Al Kα and Pd Lα x‐radiation were collected in this way. The purpose of this work was to provide systematic data on which the numerous existing expressions for φ(0) could be tested. In the final assessment procedure, in which we also included 108 data from the literature, we compared the performances of the various expressions from the literature for φ(0) and a newly developed expression of our own. Our final conclusion is that there is little to be chosen between the three to four of the highest ranking expressions.