The influence of the mean charge state on the Coulomb heating of fast diclusters through the Si〈1 1 1〉 direction

Abstract

In the present work, we report a theoretical and experimental study of the Coulomb heating of H2+ and C2+ in Si〈111〉 channel, covering an energy range from 200keV/ion to 2200keV/ion. The experimental values for Coulomb heating were obtained by combining the Rutherford backscattering spectrometry (RBS) and the particle induced X-ray emission (PIXE) techniques under channeling conditions. Theoretical values were obtained by performing classical trajectory Monte-Carlo (CTMC) simulations of the ion paths inside the 〈111〉 Si channel, using Dirac–Hartree–Fock–Slater (DHFS) results for the interionic potential. As seen for the 〈110〉 case, it is shown that the use of a DHFS potential based on the ion mean charge states in amorphous targets leads to a disagreement between the Coulomb heating values and the expected potential energies stored in the dicluster prior to the Coulomb explosion. Therefore, a numerical procedure was used in order to calculate the mean charge state values for ions traveling in Si〈111〉. The use of the resulting charge states led to a linear relationship between the Coulomb heating values and the stored potential energy per ion of the diclusters. Finally, the Coulomb heating/stored potential energy ratio amounts to about 2/3, as expected from an isotropic Coulomb explosion.