Plume-Material Interactions of Metallic Surfaces Bombarded by an [EMIM][BF₄] Electrospray Source

Experiments conducted at the University of Illinois Urbana-Champaign Electric Propulsion Laboratory investigated the effects of surface finish and vacuum baking on secondary charged species yield from metallic surfaces bombarded by a plume from a fundamental electrospray source utilizing [EMIM][BF₄]. Cation induced positive charge yields for aluminum ranged from 0.1 to 0.4 charges per incident ion and cation induced negative charge yields ranged from 0 to 0.5 charges per incident ion. Anion induced positive charge yields for the same material were low enough to effectively be 0, while anion induced negative charge yields ranged from 1 to 1.4 charges per incident ion. For stainless steel, cation induced positive charge yields varied from 0.1 to 0.3 charges per incident ion and cation induced positive charge yields ranged from 0.1 to 0.2 charges per incident ion. As with the aluminum, the anion induced positive charge yield was low enough so as to be 0, while the anion induced negative charge yield ranged from 0.9 to 1.3 charges per incident ion. The variance did not appear to result from the emitter voltage, nor did the surface finish seem to have any definitive effect on the yields. Variance in the data may arise from currently uncontrolled variations within the plume ions such as angle-of-incidence and plume current density. As a precursor to modeling similar experimental setups through molecular dynamics or with particle-in-cell methods, simulations of 1,000 all-atom [EMIM][BF₄] molecules were developed to characterize the response of an ionic liquid to the presence of an electric field. When an electric field of 6 V/nm was applied to the entire simulation domain, the number and variety of emitted species increased from 2 to 4 to 13 for 100 ps, 200 ps, and 1,000 ps, respectively.