Compensation of Time-of-Flight Drift Using an Internal Reference Ion during Long-Duration LIMAS Depth Profiling

In this study, the temporal behavior and compensation of time-of-flight (TOF) drift during long-duration depth profiling using Laser Ionization Mass Nanoscope (LIMAS) were investigated. Noble gas depth profiling by LIMAS requires detection of weak isotope signals with nanometer-scale depth resolution. However, such measurements often take several hours to a couple of days, during which TOF peak-position drift and statistical uncertainty may affect analytical precision. In this study, a ⁴He-implanted olivine substrate was analyzed as a test sample. The TOF spectra were processed by depth-layer stacking, peak extraction, and peak-position analysis. The ²⁴Mg²⁺ peak was used as a matrix-derived internal reference to monitor and compensate for TOF drift. The peak-position shifts of measured ions showed clear linear correlations with the ²⁴Mg²⁺ peak shift, indicating that the observed TOF drift is largely systematic. A ²⁴Mg²⁺-based compensation reduced the peak-position fluctuations of the other ion species to less than 1 ns and improved the mass resolving power. These results demonstrate that the ²⁴Mg²⁺ peak can be used as an internal reference for TOF drift compensation during long-duration measurements, providing a robust approach for micro- to nanoscale noble gas depth profiling using LIMAS.