Fig. 5: Normalized sodium concentration profiles in SLS post-acid treatment.

a XPS sodium depth profiling results for SLS treated in pH 1 solution of nitric acid. The dots are representative experimental data, while the shaded regions bound by lines represent the average spread of at least 3 repeat measurements. Full XPS depth profiling data for sodium can be found in SI 5. The numbers on the plots are the treatment time in days. Also shown for comparison is the data for a sample fractured in-situ in the vacuum of the XPS chamber (brown squares). b Theoretical concentration as calculated from the model with a constant dissolution rate, with \(U=2.56\times {10}^{-12}{cm}/\sec\) and \({\mathcal{D}}=5.5\times {10}^{-17}c{m}^{2}/\sec\). c Demonstration of experimental profiles with a sigmoidal shape for 7, 30, and 120 days of treatment from Fig. 5a, using the constant dissolution rate model with Gaussian convolution described by Eq. (20), with the value used for \(\sigma\) in Eq. (29) shown on the plot. The convoluted profiles were shifted by approximately \(2\sigma\) to ensure they pass through (0,0).