1. Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
2. Korea Research Institute of Standards and Science, Daejeon 305-340, South Korea
3. Department of Nano Science, University of Science and Technology, Daejeon 305-350, South Korea
4. Research Center for Dielectric and Advanced Matter Physics, Pusan National University, Busan 609-735, South Korea
5. Pacific Northwest National Laboratory, MS K8-93, P.O. Box 999, Richland, Washington 99352, USA