Correction to: Nature Materials https://doi.org/10.1038/s41563-018-0130-5, published online 9 July 2018.

In the originally published Supplementary Information file for this Article, on page 16 it incorrectly read “core radius of a= r1 and shell outer radius of b=r2”, but should have read “core radius of b= r1 and shell outer radius of a=r2”. The corrected Supplementary Information file has now been uploaded.