[1] Lawrence Berkeley Natl Lab, Natl Ctr Elect Microscopy Facil, Mol Foundry, Berkeley, CA 94720 USA
[2] Univ Calif Berkeley, Dept Mat Sci & Engn, Berkeley, CA 94720 USA
[3] Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA
[4] Lawrence Berkeley Natl Lab, Div Mat Sci, Berkeley, CA 94720 USA
[5] Lawrence Berkeley Natl Lab, Mol Foundry, Berkeley, CA 94720 USA
[6] Kings Coll London, Dept Phys, Theory & Simulat Condensed Matter, London WC2R 2LS, England
[7] Humboldt Univ, Dept Phys IRIS Adlershof, Newtonstr 15, D-12489 Berlin, Germany
[8] Monash Univ, Sch Phys & Astron, Clayton, Vic 3800, Australia
[9] Univ Melbourne, Sch Phys, Parkville, Vic 3010, Australia
[10] Univ Melbourne, Bio21 Mol Sci & Biotechnol Inst, Ian Holmes Imaging Ctr, Parkville, Vic 3052, Australia