Affiliation: | 1. Department of Mechanical and Materials Engineering, University of Nebraska, , Lincoln, NE, 68588 USA;2. Nebraska Center for Materials Nanoscience, University of Nebraska, , Lincoln, NE, 68588 USA;3. Department of Physics and Astronomy, University of Nebraska, , Lincoln, NE, 68588–0299 USA;4. State Key Laboratory of Supramolecular Structure and Materials, Jilin University, , Changchun, 130012 P. R. China |