| Popis: |
In the field of material modification and ion beam analysis, one often wants to know accurately the electronic stopping power of a compound, which defines the depth scale. Obviously, experimental data are not available for all materials of interest. Therefore theoretical models are required to yield this information. In this contribution we present approaches of how to obtain reasonably accurate estimates of the magnitude of chemical (and physical) state effects at high velocities, i.e. in the Bethe regime. First, we discuss how the I value (mean ionization potential) of a material in a certain physical state can be constructed from the I values of its constituents in their common state of aggregation, by including appropriate sub-shell I values (theoretical or experimental ones). Second, we discuss an approach to obtain the I value of a compound beyond Bragg's rule, by an empirical correction making use of the heat of formation of the compound. |
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