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Investigation of Coatings for Langmuir Probes: Effect of Surface Oxidation on Photoemission Characteristics
Author(s) -
Samaniego Joseph I.,
Wang Xu,
Andersson Laila,
Malaspina David,
Ergun Robert E.,
Horányi Mihály
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja026127
Subject(s) - langmuir probe , materials science , iridium , coating , analytical chemistry (journal) , titanium nitride , tin , langmuir , inverse photoemission spectroscopy , x ray photoelectron spectroscopy , ion , chemistry , photoemission spectroscopy , nitride , nanotechnology , plasma diagnostics , chemical engineering , layer (electronics) , metallurgy , catalysis , biochemistry , organic chemistry , chromatography , aqueous solution , engineering
Surface oxidation of Langmuir probes is an important issue for probe measurements in space environments. Followed by our previous work about the oxidation effect on the collection of ambient plasma electrons and ions, here we present its effect on photoemission from the probe surface of various materials. Photoemission is either a contamination for traditional Langmuir probes or a necessity for electric field probes in low‐density plasma. Our results show that all materials after oxidation have a varying degree of reduction in photoemission. The photoemission of copper, gold, and niobium drops most significantly followed by DAG213 (a resin‐based graphite coating), TiN (titanium nitride), and rhenium. Iridium, DAG213, and AquaDAG (graphite coating) have the largest photoemission after oxidation, making them appropriate coating candidates for electric field probes. Both DAG materials show a large photoemission enhancement after the oxidation products are cleaned off the surface. A long exposure test shows that the photoemission from iridium slowly degrades. Due to the high surface conductivity of oxidized iridium shown in previous work, it is suggested that iridium can be oxidized before flight to minimize the photoemission when being used as a coating for Langmuir probes. Overall, iridium is found to be a coating material appropriate for both electric field probes and Langmuir probes.