Long Range Chiral Imprinting of Cu(110) by Tartaric Acid T. J. Lawton, † V. Pushkarev, ‡ D. Wei, § F. R. Lucci, † D. S. Sholl, § A. J. Gellman, ‡,∥ and E. C. H. Sykes †, * † Department of Chemistry, Tufts University, Medford, Massachusetts 02155, United States ‡ Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States § School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States ∥ National Energy Technology Laboratory, U.S. Department of Energy, P.O. Box 10940, Pittsburgh, Pennsylvania 15236, United States ABSTRACT: Restructuring of metals by chiral molecules represents an important route to inducing and controlling enantioselective surface chemistry. Tartaric acid adsorption on Cu(110) has served as a useful system for understanding many aspects of chiral molecule adsorption and ordering on a metal surface, and a number of chiral and achiral unit cells have been reported. Herein, we show that given the appropriate annealing treatment, singly deprotonated tartaric acid monolayers can restructure the Cu metal itself, and that the resulting structure is both highly ordered and chiral. Molecular resolution scanning tunneling microscopy reveals that singly deproto- nated tartaric acid extracts Cu atoms from the Cu(110) surface layer and incorporates them into highly ordered, chiral adatom arrays capped by a continuous molecular layer. Further evidence for surface restructuring comes from images of atom-deep trenches formed in the Cu(110) surface during the process. These trenches also run in low symmetry directions and are themselves chiral. Simulated scanning tunneling microscopy images are consistent with the appearance of the added atom rows and etched trenches. The chiral imprinting results in a long-range, highly ordered - ( ) 2 1 6 7 unit cell covering the whole surface as confirmed by low energy electron diffraction. Details of the restructuring mechanism were further investigated via time-lapse imaging at elevated temperature. This work reveals the stages of nanoscale surface restructuring and offers an interesting method for chiral modification of an achiral metal surface. ■ INTRODUCTION The enantioselective production of chiral compounds and enantiospeci fic separation of the enantiomers of chiral compounds are of critical importance to the pharmaceutical, agricultural, and food industries that require enantiopure materials. 1−3 To generate chiral compounds without the use of costly resolving agents, enantioselective catalysts or separators, ideally being heterogeneous versus homogeneous, are required. Even though the benefits of heterogeneous asymmetric catalysts are clear, few examples exist in the literature, and the mechanism for enantioselectivity is not well understood, therefore, further study of chiral catalysts themselves, in parallel with study of enantiospecific surface chemistry on well-defined model systems is warranted. 1,4−17 One method for obtaining well-defined enantioselective surfaces involves preparation of intrinsically chiral metal surfaces. 8,18−21 Intrinsically chiral metal surfaces are formed when a single crystal is cut along a low symmetry, high Miller index plane exposing terraces, step edges, and chiral kink sites. Studies have shown that these surfaces are enantiospecific because chiral molecules have di fferent reaction rates, desorption temperatures, and adsorption energies on the two surface enantiomers. 19,20,22 While these surfaces demonstrate the possibility for chiral surface chemistry and are ideal for understanding enantiospecific molecule-surface interactions, it would be a challenge to synthesize intrinsically chiral metal surfaces with a high surface area. A second very common method for rendering a surface chiral, with potentially easier scale-up, involves the adsorption of chiral molecules onto achiral metal surfaces. 6,8,13,23−41 However, while adsorbing molecules onto a surface can produce asymmetry by creating a chiral surface template exposing chiral pockets, these layers require large flat areas of the metal surface to support ordered arrays which may not be formed on metal nanoparticles. A related approach of using molecules to chirally modify the structure of the metal substrate itself offers a potentially more practical method for inducing chirality in a catalytic substrate. Despite this advantage, there are few examples of this type of restructuring of the underlying metal surface, called chiral imprinting. 32,33,42−47 Some key studies of the chiral imprinting Special Issue: Ron Naaman Festschrift Received: February 26, 2013 Revised: July 5, 2013 Published: July 10, 2013 Article pubs.acs.org/JPCC © 2013 American Chemical Society 22290 dx.doi.org/10.1021/jp402015r | J. Phys. Chem. C 2013, 117, 22290−22297