Influence of thermal and collisional effects on the sputtering of sodium and samarium targets

Energy spectra of sputtered Na and Sm atoms investigated with a Doppler-Shift-Laser-Spectrometer are presented. The results obtained with Na and Sm targets are compared with former measurements with alkali halides. It can be shown than an increasing contribution of collision cascades to the energy spectrum results in a maximum of the sputtered flux at zero energy. It is therefore suggested that an l/(E + Esub(b))2 distribution is relevant for collision cascades instead of an E/(E + Esub(b))3 proposed by many authors. In this case the energy spectrum of sputtered Sm atoms can be explained by random collisions. The energy spectra of sputtered Na can be very well fitted if we assume that random collision cascades and slow thermal processes both contribute to sputtering. The slow thermal contribution strongly increases if the target is heated. A small thermal spike contribution can be found in the energy region from 0.2 to 0.5 eV. The binding energy of Na increases from 1.7 to 2.5 eV if the target is exposed to oxygen. In this case the slow thermal contribution is strongly reduced. (author)