Adsorbate-Induced Segregation in the Ni{111}/Au/(R,R)-Tartaric Acid System

The adsorption of the catalytically important chiral modifier, (R,R)-tartaric acid, was investigated on bimetallic Ni/Au surfaces created by annealing thin Au films on Ni{111}. Reflection adsorption infrared spectroscopy measurements revealed that the adsorption mode of (R,R)-tartaric acid depends very strongly on the surface composition. Deprotonation to produce an adsorbed bitartrate species was achieved only when small Ni clusters became available in the bimetallic surface. Medium-energy ion-scattering studies showed that, once the bitartrate species was able to be produced, significant adsorbate-induced Ni segregation was observed. Scanning tunneling microscopy (STM) investigations suggest that segregation is particularly facile in the proximity of step edges. In addition, STM revealed that the ordered (9 × 9) structure previously reported by Jacobsen et al.1 is stable even with relatively high concentrations of Ni in the surface layer