Nature Communications 6, Article number: 7482 (2015); Published 23 June 2015; Updated 21 August 2015

The financial support for this Article was not fully acknowledged. The Acknowledgements should have included the following: The atomic force microscope used in these studies was acquired under the program ‘Understanding Charge Separation and Transfer at Interfaces in Energy Materials (EFRC:CST)’, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001091.