Reducing the effects of oxygen and hydrogen on graphite SIMS measurements

Secondary ion mass spectrometry (SIMS) is a useful experimental technique for characterizing aged battery material, but the formation of a SIMS signal is complex. The method works by sputtering a material’s surface with an ion beam and analyzing the ejected secondary ions — but for graphite, which is typically used as the anode material in lithium-ion batteries, trace amounts of oxygen and hydrogen can have a major effect on the signal.

Wilhelm et al. studied how the surface chemistry of industrial graphite affects sputtering and SIMS measurement intensity to help improve graphite data interpretation.

“During the analysis of aged cells, [the] graphite substrate serves as a stable reference while the surface chemistry and deposition products accumulated over the battery’s lifetime provide vital clues for understanding degradation and aging mechanisms,” said author Gudrun Wilhelm.

Using a scanning electron microscope combined with a focused ion beam and quadrupole mass spectrometer, the researchers found that to achieve a stable SIMS signal quickly, a high ion dose should be used during the sputtering step. Though low ion doses are useful for reducing the amount of material removed, the associated reduction in secondary ion yield and SIMS signal requires significantly longer to produce a comparable, reliable SIMS intensity. Additionally, while the presence of oxygen and hydrogen affects the measured carbon cluster intensities, the group showed that normalizing the intensity to the surface-adsorbed species eliminates its influence on the measured signal.

“Collectively, these findings demonstrate that surface chemistry is as critical as conventional experimental parameters, including primary ion current and field size, and should therefore be treated as an essential factor in ensuring the reliability and accuracy of SIMS measurements on graphite-based materials,” Wilhelm said.

Source: “Impact of oxygen and hydrogen traces on the focused ion beam sputter rate and secondary ion mass spectrometry intensity detection of graphite,” by Gudrun Wilhelm, Ute Golla-Schindler, Graham Cooke, Timo Bernthaler, Ute Kaiser, and Gerhard Schneider, Journal of Vacuum Science & Technology B (2026). The article can be accessed at https://doi.org/10.1116/6.0005474 .