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O: Fachverband Oberflächenphysik

O 15: Nanostructures at surfaces: Dots, particles, clusters, arrays I

O 15.4: Talk

Monday, March 14, 2011, 15:45–16:00, WIL C107

Self-assembly of Co rings on hexagonal boron nitride — •Fabian Donat Natterer, François Patthey, and Harald Brune — Institute of Condensed Matter Physics (ICMP), Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland

Upon deposition of minute amounts of cobalt on hexagonal (h) boron nitride at low temperature, we observe the formation of nanostructures lying like a necklace around the circular part of the (12 x 12) h-BN/Rh(111) moiré unit cell. These atomic chains, bent to a closed ring of 2 nm diameter, contain at least four and up to 10 equidistant Co atoms. Low temperature scanning tunnelling microscopy results indicate short range repulsion between the ring atoms. Interactions with the electric field of the tunnelling tip or gentle annealing either transform the ring into a compact Co cluster or completely remove it from the scanning region. Surprisingly, new atomic rings renucleate in different moiré cavities or are converted from existing Co clusters at elevated temperatures. At low Co coverage, the rings are several tens of (12 x 12) unit cells apart, implying large Co adatom diffusion rates, down to the lowest studied deposition temperatures of 8 K.