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 This research was supported in part by a Wigner Fellowship through the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC, for DOE (WZ), the DOE Basic Energy Sciences (BES), Materials Sciences and Engineering Division (ARL, SJP, STP), through a user project supported by ORNL’s Center for Nanophase Materials Sciences, which is also sponsored by DOE-BES, by DOE grant DE-FG02- 09ER46554 (JL, STP), the Welch Foundation grant C-1716, the NSF grant DMR-0928297, the U.S. Army Research Office MURI grant W911NF-11-1-0362, the U.S. Office of Naval Research MURI grant N000014-09-1-1066, the National Research Foundation Singapore under NRF RF Award No. NRF-RF2013-08, and the Nanoelectronics Research Corporation contract S201006.