How to predict physical and chemical state effects in electronic stopping

In the field of material modification and ion beam analysis, one often want s to know accurately the electronic stopping power of a compound, which def ines the depth scale. Obviously, experimental data are not available for al l materials of interest. Therefore theoretical models are required to yield this information. In this contribution we present approaches of how to obt ain reasonably accurate estimates of the magnitude of chemical (and physica l) state effects at high velocities, i.e. in the Bethe regime. First, we di scuss how the I value (mean ionization potential) of a material in a certai n physical state can be constructed from the I values of its constituents i n their common state of aggregation, by including appropriate sub-shell I v alues (theoretical or experimental ones). Second, we discuss an approach to obtain the I value of a compound beyond Bragg's rule, by an empirical corr ection making use of the heat of formation of the compound. (C) 2001 Elsevi er Science B.V. All rights reserved.