Correction to: Nature https://doi.org/10.1038/s41586-019-1783-1Published online 4 December 2019

In this Article, the external surface shown in Extended Data Fig. 2b was inadvertently a duplicate of that in Extended Data Fig. 2c, even though the porosity distribution within the surface is correct. This error has no effect on any of the results or interpretations and conclusions. Figure 1 of this Amendment shows the incorrect and corrected panels of the original Extended Data Fig. 2b, for transparency. The authors would like to apologize for any confusion that this error might have caused. The original Article has been corrected online.

Fig. 1
figure 1

This figure shows the original, incorrect Extended Data Fig. 2b, and the corrected Extended Data Fig. 2b.