1. Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716, United States
2. Faculty of Natural Sciences, Quy Nhon University, Quy Nhon 590000, Vietnam
3. Nanoscale Device Characterization Division, Joint Quantum Institute, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8423, United States
4. University of Maryland, College Park, Maryland 20742, United States