1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
2. Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, 50 Nanyang Drive, Singapore 637553, Singapore
3. Institut de Ciencia de Materials de Barcelona, ICMAB-CSIC, E-08193 Bellaterra, CAT, Spain
4. Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragon (INA)—ARAID and Departamento de Fisica dela Materia Condensada, Universidad de Zaragoza, 50018 Zaragoza, Spain
5. Institucio Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, CAT, Spain
6. Singapore-Berkeley Research Initiative for Sustainable Energy, 1 Create Way, Singapore 138602, Singapore
7. NOVITAS, Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore