1. Interdisciplinary Network of Emerging Science and Technologies, Research Center, Philip Morris USA, Richmond, Virginia 23234, Physics Department, Virginia Commonwealth University, Richmond, Virginia 23284, Research Center, Philip Morris USA, Richmond, Virginia 23234, NIST Center for Theoretical and Computational Nanosciences, National Institute of Standards and Technology, Gaithersburg, Maryland 20899P, and Harrington Department of Bioengineering, Arizona State University, Tempe, Arizona 85287