[1
]Department of Materials Science and Engineering, National University of Singapore,
Singapore 117575
[2
]Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese
Academy of Sciences, Beijing 100190, China
[3
]NUSNNI-NanoCore, National University of Singapore, Singapore 117411
[4
]Imaging and Characterization Core Lab, King Abdullah University of Science and Technology
(KAUST), Thuwal 23955-6900, Saudi Arabia
[5
]Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link,
Singapore 117603
[6
]School of Materials Science and Engineering, University of New South Wales (UNSW),
Sydney, NSW 2052, Australia