1. Physics Department, St. Lawrence University, Canton, New York 13617, USA
2. Department of Electronic and Electrical Engineering, South University of Science and Technology of China (SUSTC), Shenzhen 518055, China
3. Department of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech, Building 345 East, DK-2800 Kongens Lyngby, Denmark
4. Danish National Research Foundation's Center for Individual Nanoparticle Functionality (CINF), Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark