In quest of the spike: energy dependence of the sputtering yield of zinc bombarded with neon and xenon ions

Sputtering yields of Zn were determined for bombardment with Ne and Xe ions at normal incidences in the energy range 0.2-20 keV under ultrahigh vacuum conditions. Mass selection was employed and the energy spread was limited to a few electron volts. High fluences of the order of 3 X 1017 cm-2 were used to obtain stationary state yields. The yields were determined from accurate weighing of the samples prior to and after the irradiation stage. The measured yields obtained in low current density bombardments are in excellent agreement with predictions from Sigmund's linear cascade theory. There is no evidence of an anomalous, spike-like, cascade behaviour, in sharp contrast to what could be expected on the basis of experimental systematics or theoretical considerations. Yields measured for 20 keV Ne+ bombardment of Zn at high flux show a sharp deviation from the Sigmund estimate. Tests have revealed this to be induced by beam heating of the target. The huge yields observed, however, cannot be attributed to a simple evaporation process but must be interpreted as tentative evidence of a so-called thermal spike. (Auth.)