Secondary electron emission due to multi-species iodine ion bombardment of different target materials

Ion-induced secondary electron emission (SEE) is a fundamental surface interaction that strongly influences many plasma discharges. Recently, interest in iodine plasmas is growing due to new material processing and space propulsion applications, but data for SEE yields due to iodine ion bombardment remain scarce. Additionally, due to the formation of multiple ion species in typical iodine plasmas and surface chemical reactions leading to iodide layer formation, the effective SEE yield is expected to differ from that for individual ion species on clean surfaces. In this work, we measure the SEE yield of multi-species iodine ion beams bombarding different target materials (Mo, W, Al, Ti, Cu, carbon-carbon, and steel) in the energy range of 0.6–1.4 keV. An ion beam is produced by extracting and accelerating ions from a gridded ion source based on an inductively coupled plasma (ICP). SEE yields of downstream targets are measured using a conventional electrostatic probe technique, and the ion beam composition is determined using time-of-flight spectrometry. The beam is composed predominately of atomic (⁠$I+$⁠) and molecular (⁠$I2+$⁠) ions whose ratio changes depending on the ICP power. Yields depend strongly on the target material and beam composition and vary between $0.05$ and $0.4$ depending on whether potential or kinetic emission processes dominate.