Delay times in the sputtering of atoms from alkali-halide crystals during low-energy electron bombardment

Delay times in the sputtering of atoms from RbI, RbBr and NaCl by 540 eV electrons were investigated. This was done by simultaneously using the correlation technique and a slotted disc velocity selector. We observed delays in thermally ejected alkali and halogen atoms. These times were found to be independent of target temperature and are ascribed to lifetimes of excitons. Non-thermal halogen atoms are always sputtered without any delay.