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Atomic-scale roughness of an intrinsically chiral metal surface

We have used STM to reveal the atomically rough nature of an intrinsically chiral metal surface, Cu{531}. This is an example of a kinked-stepped fcc surface that is at an orientation devoid of all bulk mirror symmetry. One might therefore anticipate such surfaces having potential for enantiospecific heterogeneous catalysis involving chiral and pro-chiral molecular adsorbates.

Experimentally, we find that the clean Cu{531} departs strongly from ideal bulk termination. STM images recorded at 77 K show a high degree of atomic-scale roughness. Intact {531} meshes co-exist with a rich variety of steps, adatoms, vacancies, clusters and pits. Perhaps surprisingly, sharp LEED patterns can be recorded from such surfaces.

Simple nearest-neighbour bond-counting arguments rationalise the roughness. Creating a vacancy breaks six n-n bonds, while placing an adatom in a lattice site makes six n-n bonds. Adatom-vacancy annihilation therefore does not give the enthalpy reduction that normally drives ordering on low-index surfaces.

The thermal roughness of Cu{531} differs in detail from that of chiral kinked-stepped fcc surfaces having wider close-packed terraces, specifically the Cu and Pt{643} surfaces studied by other groups. We attribute the differences to repulsive step-step interactions: these oppose step meandering for small step-step spacings.

Figure 1. STM image of atomically rough Cu{531} at 77 K. Each bump is a Cu atom in the (local) outermost layer. Image size: 20 x 20 nm2.

Related publications

"Atomic roughness of an intrinsically chiral surface orientation of an fcc metal: Cu{531}"
M.L. Clegg, S.M. Driver, M. Blanco-Rey and D.A. King
J. Phys. Chem. C 114 (2010) 4114

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Last updated 12/3/2010 by mb633 -at-