1. Department of Mechanical and Materials Engineering, University of Nebraska−Lincoln, Lincoln, Nebraska 68588-8286, United States
2. Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
3. Department of Chemical and Biomolecular Engineering, University of Nebraska−Lincoln, Lincoln, Nebraska 68588-8286, United States
4. Department of Physics, Harbin Institute of Technology, Harbin 150001, China
5. Department of Mechanical Engineering, Colorado School of Mines, Golden, Colorado 80401-1887, United States