Impact of oxygen and hydrogen traces on the focused ion beam sputter rate and secondary ion mass spectrometry intensity detection of graphite

Trace amounts of oxygen and hydrogen can strongly influence the formation of negative carbon ions during focused ion beam–secondary ion mass spectrometry (SIMS) analysis of graphite. In this study, the sputtering behavior of graphite and the detection of single and clustered carbon ions were investigated under systematically varied measurement conditions. Experiments were performed by varying the primary ion current and the analysis field size, enabling a systematic evaluation of ion dose effects. A linear relationship between sputter rate and ion dose was observed. The sputter yield increases at low ion doses and stabilizes at approximately 1.6 C atoms/Ga+ ion for ion doses above 15 nC/μm2. Large analysis fields lead to a decrease in sputter yield accompanied by increased scatter, indicating the onset of sample swelling. Signal stability strongly depends on ion dose. At high ion doses, stable sputtering conditions are reached within about 1 min, whereas up to 20 min are required at low ion doses. Under stable conditions, mass spectral peak heights correspond well with constant signal levels observed in multiple ion detection profiles. Carbon ion intensities vary strongly with measurement parameters but become stable when normalized to simultaneously detected oxygen, hydrogen, or hydroxide signals. These results indicate that trace surface impurities modify the electronic structure of graphite and significantly affect negative ion formation. The findings highlight the importance of surface chemistry for the interpretation of SIMS measurements, particularly in the analysis of graphite-based lithium-ion battery materials.