1. Materials Sciences Division, Molecular Foundry, and Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Institut Català d' Estudis i Recerca Avançat and Institut Catalá de Nanotecnologia, Bellaterra 08193, Barcelona, Spain, Institut de Ciència de Materials de Barcelona, (ICMAB-CSIC), Campus UAB, Bellaterra 08193, Spain, and Department of Chemistry, University of California at Berkeley, Berkeley, California 94720