“…The Fundamental Parameters (FP) method used to reduce the on-site XRF data does not yet usually have direct metrological traceability, although reference-free (off-site) measurements are now increasingly feasible, 9 and signicant progress is being made in establishing robust uncertainty budgets for this sort of metrology. 10 Therefore, independent Ion Beam Analysis (IBA) methods have been used to certify nitrogen standards for these GST lms. IBA is a toolbox of off-site complementary methods including elastic backscattering (EBS: Rutherford backscattering, RBS, is a special case of EBS), nuclear reaction analysis (NRA) and particle-induced X-ray emission (PIXE, another IBA technique entirely comparable to XRF except for the atomic excitation mechanism): IBA is commensurate with, but independent of, XRF; in particular, IBA is naturally a depth proling technique 11 whereas XRF has little or no direct depth sensitivity except in grazing incidence (GIXRF), especially with X-ray reectometry (XRR) methods.…”