[1] Lawrence Berkeley Natl Lab, Mol Foundry, Berkeley, CA 94720 USA
[2] Univ Glasgow, Sch Phys & Astron, Glasgow G12 8QQ, Lanark, Scotland
[3] Univ Oxford, Dept Mat, Parks Rd, Oxford OX1 3PH, England
[4] PNDetector GmbH, Otto Hahn Ring 6, D-81739 Munich, Germany
[5] PNSensor GmbH, Otto Hahn Ring 6, D-81739 Munich, Germany
[6] JEOL Ltd, 3-1-2 Musashino, Akishima, Tokyo 1968558, Japan
[7] Forschungszentrum Julich, Ernst Ruska Ctr ER C Microscopy & Spect Electrons, D-52425 Julich, Germany