Improving the elemental and imaging accuracy in atom probe tomography of (Ti,Si)N single and multilayer coatings using isotopic substitution of N

This study addresses the challenges in analyzing (Ti,Si)N coatings using atom probe tomography (APT). Overlapping mass-to-charge state ratios in APT mass spectra hinder unambiguous identification of Si and N, thus, isotopic substitution of naturally abundant nitrogen by ¹⁵N-enriched nitrogen was applied to disentangle the mass-spectral overlaps. A series of model coatings, namely, Ti-N, Si-N, and Ti-Si-N single layer coatings were utilized to investigate elemental accuracy, while their corresponding multilayer coatings were used to assess lateral resolution and imaging accuracy. The coatings were sputter-deposited using i) naturally abundant nitrogen and ii) ¹⁵N-enriched nitrogen, respectively. Subsequently, the coatings were analyzed with a LEAP 5000 XR atom probe. Accuracy in obtained concentrations was cross-validated with elastic recoil detection analysis (ERDA) combined with Rutherford backscattering spectrometry (RBS). The investigation showed that isotopic substitution allows to differentiate the Si and N peaks in the mass spectra and significantly reduces compositional discrepancies between APT and ERDA/RBS results. Despite remaining minor peak overlaps, which can result in inaccuracies in determining the elemental composition, isotopic substitution has proven to be an effective method for peak differentiation and correcting the obtained elemental composition of Ti-Si-N. Moreover, isotopic substitution can predominantly increase the elemental accuracy and imaging accuracy of APT measurements of multilayer coatings.