1. School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore
2. Ernst Ruska-Centre for Microscopy and Spectroscopy
with Electrons (ER-C) and Peter Grünberg Institute (PGI), Forschungszentrum Jülich, 52428 Jülich, Germany
3. Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, 638075 Singapore