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

In the present work, we report a theoretical and experimental study of the Coulomb heating of H2+ and C2+ in Si〈1 1 1〉 channel, covering an energy range from 200 keV/ion to 2200 keV/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 〈1 1 1〉 Si channel, using Dirac-Hartree-Fock-Slater (DHFS) results for the interionic potential. As seen for the 〈1 1 0〉 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〈1 1 1〉. 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.