Nature Nanotechnology 11, 1031–1038 (2016); published online 6 December 2016; corrected after print 14 December 2016

In the original version of this Review Article Feng Pan's affiliation should have read: 'School of Advanced Materials, Peking University, Shenzhen Graduate School, Shenzhen 518055, PR China'. This has been updated in the online versions of the Review.