1. Division of Materials Science and Engineering
2. Division of Bionanotechnology, Kyungwon University, Sungnam city 461-831, Korea
3. Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea
4. National Creative Research Initiative Center for Semiconductor Nanorods and Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
5. Department of Energy Engineering, Hanyang University, Seoul 133-791, Korea
6. Department of Materials Science and Engineering, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801