time was essentially identical to the Rbaseline slope measured just before the start of the long etching period. Thus, the final, baseline-subtracted N2O etching rate was essentially zero, i.e., this NP passivated against N2O attack after ~9 hours of combined etching and sublimation, which resulted in total mass loss of ~5 MDa, or ~30% of the mass at the beginning of the first etching period.