1. School
of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore
2. Environmental
Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
3. Department
of Physics, Tamkang University, New Taipei City 25137, Taiwan
4. Department
of Applied Science and Engineering, Indian Institute of Technology Roorkee, Saharanpur Campus 247667, India
5. CREATE , 1 CREATE Way, #10-02 CREATE
Tower, 138602 Singapore