The Effects of Ultra-High Vacuum on Surface Contamination

Ultra-high vacuum (UHV) is essential to many surface characterization techniques and is often employed with the intent of controlling or limiting contamination. However, the effect of UHV on surface contamination is not well-understood, adding error to surface elemental characterization techniques and complicating surface-sensitive manufacturing processes. In this work, we investigated the surface composition of gold samples with different initial levels of contamination under UHV for approximately 24 hours through experiments and physical modeling. Results show that the surface carbon concentration under UHV follows a similar evolution as in ambient air and can be explained by molecular adsorption-desorption competition theory. Pristine gold surfaces adsorbed hydrocarbons over time under UHV, whereas pre-contaminated surfaces lost hydrocarbons by desorption. This work provides quantitative evidence of temporal changes in surface contamination under UHV and highlights routes to mitigate these effects in precise experiments or processes conducted under UHV.