The Real Structure of Naturally Chiral Cu{643}

Achiral metals can be cut, polished, and cleaned in such a way that they are terminated by surfaces on which all of the kink sites along the step edges are of the same chirality. The most studied of these surfaces is the {643} facet of Cu, which has been shown to interact enantiospecifically with chiral molecules. In order to fully exploit the potential of these surfaces for enantioselective chemistry, elucidating an atomic-scale picture of the active sites is crucial. Low-temperature scanning tunneling microscopy was used to study the structure of a Cu{643} crystal that had been thermally roughened at 1000 K. Images recorded at 78 K revealed that the real structure of Cu{643} is much more complex than the ideal structure. The number of chiral kink sites was quantified and compared to that expected for the ideal Cu{643} structure. Importantly, atomic resolution imaging revealed that the absolute chirality of the surface is preserved; however, thermal roughening led to a reduction in the absolute number of kinks.