Abstrakt
Probably the most abundant dust in space constitutes silicates. When the dust grain is exposed to energetic electron or ion beams it can attain a large surface potential which is limited by field ion emission.
It is generally expected that the field ion emission is controlled by the surface electric field, and pressure and composition of the ambient atmosphere. In our study, we have used spherical glass dust grains with diameters around 1 micron charged to several kV.
Such charging creates the electric field in the range of 109 V/m leading to observable field ion emission. A positive charge of the dust grain can be reached not only by ion bombardment but, under some circumstances, by electrons as well.
Contrary to the expectations, when charged by electrons, the discharging characteristics depends on the obtained specific charge, the energy of impinging electrons and charging current density. Moreover the discharging shows an increase of the discharging current in the beginning.
We show that such behavior is caused by diffusion of positive holes inside the grain through the influence of an inner electric field and enhanced temperature.