1. California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
2. Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
3. Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States
4. Department of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, China
5. Department of Psychiatry and Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, Los Angeles, California 90095, United States