Thermal spike model for heavy ion induced desorption from surfaces

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Abstract
Yields of molecular ions desorbed from surfaces by energetic heavy ions have been studied using a thermal spike model. A temperature profile was assumed which is appropriate for high linear energy transfer (LET) ion‐solid interactions. The desorption kinetics were assumed to follow a simple Arrhenius rate law which has been found to be useful in understanding desorption due to rapid temperature jumps. With these assumptions, we have fit recent desorption experiments where the exciting ions had a LET in the range of 10–100 MeV cm2 mg−1 and where the desorbed molecules ranged from valine to insulin. The thermal spike model predicted nonlinear dependence of the yield on LET at lower LET and a nearly linear dependence of the yield on LET at high LET. These features are in good agreement with the experimental data. We also considered modified models which included a loss channel due to fragmentation. These models gave somewhat better agreement with the experimental data. The parameters obtained in these fits were analyzed using sensitivity analysis to determine their uncertainties and to determine the interdependencies between parameters. The best fit model has been used to predict desorption yields at higher and lower LET and for different initial energy densities in the ionized track.