Energy Distributions of Secondary Electrons Under Different Conditions

Secondary emission invoked by energetic electrons can charge dust grains either positively or negatively depending on the grain size, secondary emission yield and electron energy. Emission properties of the grain surface depend on grain's charging history (the impact of energetic ions etc.), but these processes are not well understood.We have carried out a systematic study of aforementioned effects using micron-sized gold spheres as a dust simulants. A single grain was trapped in an electrodynamic trap and exposed to electron and/or ion bombardment in energy range from about 100eV to 10keV. Sophisticated techniques allow us to determine the equilibrium grain charge (surface potential) as a function of the electron beam energy as well as currents flowing to and from the grain, and to separate the current of secondary electrons and determine the energy distribution of these electrons