Auto-ionization of LiF Grains

Low-affinity materials (as MgO, CaO, LiF) are known to vary their Mie scattering profile with a changing charge. These materials are also predisposed to autoionize themselves. Although the oxides, opposite to lithium fluoride, are expected within the space environment, the presented investigations were carried out on LiF, since the aforementioned process shall be more pronounced. We are trapping a single grain in an electrodynamic quadrupole where the dust charge and its evolution can be estimated. By precise observations, we can register isolated hops of the grain charge which indicate the autoionization. A rate of this process varies with previous treatments of the object. While fresh grains exhibit one or a few hops within first 24 hours, the period between hops decreases to seconds, and the grain increases its charge by tens of elementary charges when the grains are treated by the electron beam with energy of 0.5-1 keV. On the other hand, ion treatment seems to stop the autoionization. The paper summarizes our observations and attempts to characterize the process itself.