Nanostructured chiral surfaces

Abstract

Chiral organic surfaces were generated via adsorption of the pure enantiomers of heptahelicene, a helically shaped aromatic hydrocarbon, on a Ni(111) surface in ultra high vacuum. Time-of-flight secondary mass spectrometry (ToF-SIMS) revealed that the molecule stays intact at room temperature. The formation of a two-dimensionally ordered structure at monolayer coverage is observed via low-energy electron diffraction (LEED) and scanning tunnelling spectroscopy (STM). For creation of a chiral metal film, the chiral organic monolayer was subjected to subsequent metal physical vapour deposition. Differences in morphology of grown copper and palladium films were only observed when heptahelicene was adsorbed prior to deposition. No screw dislocations with preferred handedness were observed when the pure enantiomers were used.

Intermediate structures in two-dimensional molecular self-assembly

“…4(a) top, C 30 H 18 , [7 ] H] on metal surfaces is an exciting chapter of surface chirality. While on nickel surfaces no extended ordering phenomena has been found [24][25][26], a pronounced transfer of chirality into mono-and multilayered structures, manifested by the formation of extended chiral motifs, was observed for the pure enantiomers on Cu(111) [27,28]. Interestingly, mirror domains have been observed for the racemate at the same surface, indicating at a first glance a lateral resolution of the enantiomers [29].…”

Stereochemistry of 2D Molecular Crystallization

“…[15] 2D crystallization experiments with helicenes and ortho-annulated carbohelicenes which have outstanding material and chiroptical properties, [16] showed interesting behavior. [17,18] On Cu(111) heptahelicene ( [7]H, C 30 H 18 (Fig. 2a)) forms racemic 2D crystals.…”

The Physical Chemistry of Chirality

“…Ernst et al adsorbed heptahelicene on a Ni (111) surface in ultrahigh vacuum (56). The two dimensional ordered structure of intact molecules was studied using Low Energy Electron Diffraction (LEED) and STM, and were found to be close packed.…”