1. Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801, USA
2. Laboratory for Optical Physics and Engineering, University of Illinois, Urbana, Illinois 61801, USA
3. N. Holonyak, Jr. Micro and Nanotechnology Laboratory, University of Illinois, Urbana, Illinois 61801, USA
4. Department of Civil and Environmental Engineering, University of Illinois, Urbana, Illinois 61801, USA
5. Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
6. Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801, USA
7. Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois 61801, USA