Attachment of mobile particles to non-saturable traps

Abstract

Abstract Thermal desorption spectra have been measured for helium attached to xenon atoms in a tungsten crystal. The xenon was implanted at 1.5 keV and annealed to 2150 K, and the helium then injected at 250 eV along the <100> direction normal to the crystal surface. The binding energy of the helium was found to increase monotonically with the number of helium atoms occupying the trap, from 1.2 eV for a single atom to ≈2.1 eV for 7 to 10 atoms. At still higher injected doses, the attachment of up to 100 helium atoms to each trap has been observed. The binding energy continues to increase to ≈4 eV for 100 atoms, and the apparent trapping radius increases by a factor of four from the empty trap value of 3.3 Å.