Total and Differential Sputtering Properties of Disordered Carbons

Carbon contamination during ground-testing of electric propulsion (EP) thrusters complicates erosion measurements and lifetime assessment. An isotopically enriched carbon tracking diagnostic has been developed to isolate carbon flux from specific sources during EP testing to de-couple facility- and thruster-sourced carbon; however, the suitability of the enriched material as a surrogate for graphite has not been quantified. This work compares the microstructure, surface topology, and sputtering properties of a high-density graphite, an amorphous carbon (a-¹²C), and an enriched amorphous carbon (a-¹³C) to determine whether isotopic enrichment or structural disorder meaningfully alters the sputter yield of carbon. X-ray diffraction and Raman spectroscopy show a progression in structural disorder from HDG to a-¹³C to a-¹²C, while optical profilometry indicates similar surface topology, with the ¹³C material being moderately smoother. Total sputter yields under 250 eV Kr⁺ bombardment were measured through mass loss and found to be statistically indistinguishable across all materials (Y(a-¹²C)/Y(HDG) = 0.96 ± 0.04 and Y(a-¹³C)/Y(HDG) = 1.06 ± 0.05). Additionally, angularly resolved flux data from a prior campaign were reanalyzed to evaluate the differential sputtering behavior of the enriched target, showing excellent agreement with empirical graphite differential sputter yield distributions. Together, these results indicate that a-¹³C can be utilized as a proxy for tracking sputtered graphite and requires no material-specific correction factors when used for carbon-transport mapping during EP testing.