Effect of diffusion of valence holes to defect distribution in swift heavy ion tracks in alkali-halides
poster presentation: Monday 2010-08-23 05:00 PM - 07:00 PM in section Cluster ions, single ion, swift heavy ions, highly charged ions
Last modified: 2010-08-11
Abstract
Irradiations with swift heavy ions (SHI, M≥20mp, E>1 MeV/u) result in large energy deposited to the electronic subsystem of a solid (10 – 70 keV/nm). A small part of this energy transferred to the lattice can cause structure and phase transformations in nanometric SHI tracks ranging up to a hundred μm. The kinetics of these transformations depends on peculiarities of relaxation of the defect ensemble created in SHI tracks.
Alkali halides are the excellent system for investigation of the defect kinetics in SHI tracks because (a) the excess electronic energy can be converted there into point defects via decay of self-trapped excitons generated by valence holes forming during target ionizations, and (b) these defects (color centers) and their aggregates can be detected by the spectroscopy technique.
We demonstrate that spatial propagation of created valence holes is responsible for formation of the defect halos of SHI tracks in alkali-halides. For this purpose the radiuses of the defect halos were extracted from the dependencies of the defect concentrations on fluence in LiF and NaCl crystals irradiated at UNILAC accelerator (GSI) with different ions (energies up to 11 MeV/u) at cryogenic and room temperatures. The tested Monte-Carlo code was used to determine the initial spatial distributions of valence holes created by SHI and fast electrons generated in tracks.
For all ions the observed parameters of the defect halo can not be fitted by only the initial distribution of valence holes in a SHI track. We conclude that this halo is formed due to spatial spreading of valence holes during short times (~1 ps) before their self-trapping. This gives us also ability for estimation of the effective diffusion coefficient of valence holes in excited SHI tracks (Dh ~ 1-10 cm2/s).Author(s) affiliation:
Nikita Medvedev, TU Kaiserslautern, Erwin Schroedinger Str. 46, D-67663 Kaiserslautern, Germany
Alexander Volkov*, Russian Research Center, Kurchatov Institute, Kurchatov Square 1, 123182 Moscow, Russian Federation
Christina Trautmann, Gesellschaft für Schwerionenforschung, Planckstr.1, 64291 Darmstadt, Germany
Baerbel Rethfeld, TU Kaiserslautern, Erwin Schroedinger Str. 46, D-67663 Kaiserslautern, Germany
Reinhard Neumann, Gesellschaft für Schwerionenforschung, Planckstr.1, 64291 Darmstadt, Germany
*presenting author