Chiral metal surfaces from the adsorption of chiral and achiral molecules

Chiral surfaces, capable of existing in two distinguishable mirror forms that cannot be superimposed, are attracting worldwide attention. The adsorption of complex organic molecules provides a means of introducing the ultimate discrimination function of chirality to a metal surface. Here, a comparison of the chiral tartaric acid (HOOC-CHOH-CHOH-COOH) molecule and the achiral succinic acid (HOOC-CH2-CH2-COOH) molecule on a Cu(110) surface is presented. For both molecules, two-dimensional assembly is found to depend strongly on molecule-metal bonding interactions, whereas the presence/absence of the OH groups causes subtler, second-order effects on the self-assembled structure. The driving force for creating chiral organisations is shown to arise from adsorption-induced asymmetrisation, via molecular distortion and/or metal reconstruction of the local adsorption unit. The macroscopic chirality of the surface is then determined by whether nucleation points of both chirality can be equally created, or whether non-degeneracy can be introduced to favour one chirality.