Sputtering by fast ions based on a sum of impulses

A simple, unifying description of the sputtering of solids by fast ions is obtained by summing impulses. For both electronic and collisional energy deposition, the scaling of the yield versus energy deposition per unit path length (dE/dx) is in agreement with experiment in three different regions of (dE/dx), each exhibiting different ejection characteristics: single events, ‘‘diffusive spike,’’ and ‘‘pressure pulse.’’ The latter is a volume ejection mechanism for which the yield scales as (dE/dx${)}^3$ at high (dE/dx) when the ion penetration depth is large. This mechanism can account for the observed dependence of the yield of intact biomolecules ejected from the solid state and the ejection angles for the intact molecular ions.