1. School of Materials Science and Engineering Nanyang Technological University Nanyang Avenue Singapore 639798 Singapore
2. Energy Research Institute @NTU, ERI@N, Research Techno Plaza, X-Frontier Block, Level 5 50 Nanyang Drive Singapore 637553 Singapore
3. Laboratory of Photonics and Interfaces, Department of Chemistry and Chemical Engineering Swiss Federal Institute of Technology Station 6 1015 Lausanne Switzerland
4. Department of Materials Science and Engineering University of California Berkeley CA 94720 USA
5. National Center for Electron Microscopy, Molecular Foundry, Lawrence, Berkeley National Laboratory Berkeley CA 94720 USA