The influence of geometry and specific electronic and nuclear energy deposition on ion-stimulated desorption from thin self-supporting membranes

We investigate the dependence of the yield of positive secondary ions created upon impact of primary 4He+, 11B+ and 22Ne+ ions on geometry and electronic and nuclear energy deposition by the projectiles. We employ pulsed beams in the medium energy regime and a large position-sensitive, time-of-flight detection system to ensure accurate quantification. As a target, we employ a single crystalline Si(100) self-supporting 50 nm thick membrane thus featuring two identical surfaces enabling simultaneous measurements in backscattering and transmission geometry. Electronic sputtering is identified as the governing mechanism for the desorption of hydrogen and molecular species found on the surfaces. Nevertheless, larger energy deposition to the nuclear subsystem by heavier projectiles as well as due to the directionality of the collision cascade appears to act in synergy with the electronic energy deposition leading to an overall increase in secondary ion yields. A higher yield of ions sputtered from the matrix is observed in transmission (forward) geometry only for B and Ne ions, consistent with the observed role of nuclear stopping.