1. Department of Materials Science and NanoEngineeringRice University Houston TX 77005 USA
2. Smalley‐Curl InstituteRice University Houston TX 77005 USA
3. School of Materials Science and EngineeringNorthwestern Polytechnical University Xi'an 710072 China
4. Department of PhysicsFudan University Shanghai 200433 China
5. Department of ChemistryRice University Houston TX 77005 USA
6. Shared Equipment AuthoritySIMS laboratoryRice University Houston TX 77005 USA