The Study of Dust-Grain’s Field Ion Emission

Understanding of various charging processes of dust grains is important in many different industrial applications as well as in the space research and theoretical studies of charging. An impact of energetic ions onto a dust grain leads to transfer of charge to the grain. This effect increases the charge of the dust grain until an equilibrium value is reached. After charging, the ion beam is switched off, the grain is spontaneously discharging. The discharging current can be attributed to field ionization of a gas surrounding the grain or ion field evaporation of the grain material and thus it would be a function of the surface field intensity. However, our previous study indicated that the main process discharging the dust grain is the field ion desorption of beam ions deposited on the grain surface. This paper enhances mentioned studies. We used a spherical Au grain charged by the beam of He ions. We have found that the discharging current strongly depends on the structure of the grain surface (especially, on the bonding energy of beam ions on the grain surface), not only on the surface field intensity.