1. Smalley-Curl Institute Applied Physics Program, Rice University, Houston, TX 77005, USA.
2. Department of Chemistry, Rice University, Houston, TX 77005, USA.
3. Department of Physics and Astronomy, Rice University, Houston, TX 77005, USA.
4. School of Chemistry and Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
5. Materials Science and Nanoengineering, Rice University, Houston, TX 77005, USA.
6. Department of Electrical and Computer Engineering, Rice University, Houston, TX 77005, USA.