Correction to: Nature Materials https://doi.org/10.1038/s41563-017-0013-1 published online 12 February 2018.

In the version of this Article originally published, the units of the y axis of Fig. 3b were incorrectly given as ‘106 cm2 s–1’; they should have been ‘10–8 cm2 s–1’. This has been corrected in the online versions of the Article.