Reliable Atom Probe Quantification of Carbon in Non-Stoichiometric TiCx: Effects of Laser Energy and Correction of Carbon Loss

Accurate carbon quantification in TiCx by atom probe tomography (APT) is strongly affected by the evaporation of carbon-containing molecular ions, detector dead time and peak overlap. Here, APT mass spectra, hit multiplicity and correlation histograms acquired at 40–400 pJ were analyzed to characterize laser-energy-dependent evaporation. With increasing laser energy, carbon shifted toward C2+–C5+ molecular ions and Ti-C complexes, including TiC+, TiC2+–TiC5+ and Ti2C22+. The fraction of detected carbon carried by molecular ions increased from 47% to 98%, while the uncorrected C/Ti ratio decreased from 0.52 to 0.26. Multiplicity and correlation analyses indicated that carbon-rich molecular ions were susceptible to incomplete registration within the detector dead time. After correction for dead-time-related losses of C2+ and C+ at 6 and 12 Da as well as for the 24 Da overlap between 48Ti2+ and C2+, the C/Ti ratio increased to 0.92 at 40 pJ and 0.83 at 60 pJ, approaching the XRD-derived range of 0.85–0.95. At higher energies, the correction remained insufficient because the method does not explicitly account for C3+–C5+ molecular-ion losses, whose broad peaks and unresolved minor-isotope peaks prevent reliable isotope-based correction. Therefore, among the investigated conditions, 40 pJ is preferable for reliable APT carbon quantification in TiCx.