Bibliographical noteFunding Information:
D.L. acknowledges the financial support of the Japanese Society of the Promotion of Science (JSPS) Fellowship for work carried out at the Energy Electronics Institute,AIST. H.Z. thanks M. Ichihara for help in TEM observations, and acknowledges partial research funding from JSPS, Japan Science and Technology Agency, AIST. Correspondence and requests for materials should be addressed to H. Z. Supplementary Information accompanies the paper on www.nature.com/naturematerials
Supported in part by the Deutsche–Israel Program, the Israel Science Foundation and the US–Israel Binational Science Foundation.We are grateful to Vladimir Ezersky for assistance in the HRTEM measurements. Correspondence and requests for materials should be addressed to U.B. Supplementary Information is available on the Nature Materials website (http://www.nature.com/naturematerials).