Influence of Charging Conditions on Dust Grain’s Field Ion Emission

The research of charging processes of various types of dust grains is important for understanding of the role of dust in dusty plasmas in a space as well as in applications. One of the very important charging process is field ion emission. The field ion emission can limit the positive charge on the dust grain because the positive ions leave a grain surface due to a strong electric field. We analyzed many discharging characteristics of an Au grain of 0.57 μm of radius measured under different conditions (the ion beam energy, ion species, total dose of ion bombarding) and found that the discharging current is determined not only by the surface field intensity but it strongly depends on the structure of the grain surface and on the history of measurements. We have found that the duration of charging (or total dose of the ions impinging the grain) is one of the important parameters. The dose of bombardment determines the number of implanted ions. Since their diffusion toward the surface is very slow (hours for 5 keV ions), the history of the grain should be considered in interpretation of the results.