Statistics of electron and ion emission from single massive cluster impacts
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abstract
We demonstrate several fundamental characteristics of coemissions of secondary ions and electrons from homogeneous targets. The custom-built device consists of an electron microscope equipped with a fast digital camera, and a time-of-flight secondary ion mass spectrometer. The device operates in event-by-event emission/detection mode with synchronized detection of electrons and ions emitted from single projectile impact. The data are in the form of images of detected electrons which correspond to coordinates of impacts. Further, for the coordinates of each impact, there is also the ion information from that impact. The bombardment of different homogenous targets (Gramicidin S, Glycine, Guanine, Al, Au) by 15 keV C 60+ and 30 keV C 602+ shows abundant coemission of negative ions and electrons. We compute from the data the distribution of number of electrons detected per projectile impact. Our observations indicate that electrons are emitted independently from the type or number of the coemitted negative ions. The abundant coemission of negative ions and electrons from homogenous targets implies strong electron excitation in the energized nanovolume. Independence of emission of negative ions and electrons indicates that the mechanism of ionization is due to electron exchange between the emitted species in the excited nanovolume rather than via electron attachment. Copyright 2010 John Wiley & Sons, Ltd.
