Sputtering of alkali halides studied by a mass selected time of flight spectroscopy

Energy distributions of alkali and halogen atoms sputtered with a low-energy electron beam have been measured for NaCl, CsI and KBr single crystals. Energy spectra for alkali atoms can be described by the Maxwell-Boltzmann distribution. In case of halogen atoms, for some crystals, an additional, non-thermal component appears. The behaviour of this component was investigated as a function of the target temperature, the beam energy, its current density and the ejection angle. The results can be described by creation of focused replacement sequences and H-centre migration model. The ejection of non-thermal halogen atoms from the (100) surface of KBr single crystal is strongly forward peaked along the normal. This effect is caused by a thin damage layer appearing on the surface due to a strong nonstoichiometry of the erosion process itself.