Metal-Organic Superlattices Induced by Long-Range Repulsive Interactions on a Metal Surface

TL;DR

This paper demonstrates that chains of atoms and molecules on a metal surface form a superlattice due to long-range Coulomb repulsive interactions, supported by experimental STM data and DFT calculations.

Contribution

It provides evidence for long-range Coulomb repulsion governing the superlattice formation on a metal surface, combining experimental STM analysis with theoretical DFT modeling.

Findings

Interchain distances deviate from randomness, indicating repulsive interactions.

Experimental data fits a 1/d Coulomb-like potential.

DFT shows charge depletion at chain edges due to molecular polarity.

Abstract

Chains of Na atoms and dicyanovinyl-quinquethiophene (DCV5T-Me2) molecules with ionic bonds form a superlattice on Au(111). Through a detailed analysis of the interchain distances obtained from scanning tunneling microscopy images at various molecular coverages, we found that the chain arrangement substantially deviates from a random distribution of noninteracting chains. Instead, the distribution of chain spacings provides evidence for the existence of an interchain long-range repulsive potential. Furthermore, the experimental results can be modeled by a repulsive potential with a 1/d distance dependence, characteristic of Coulomb interactions. Density functional theory calculations of free-standing molecular chains reveal a charge depletion at the periphery of the chains, which is attributed to the intrinsic polar property of the molecule and is responsible for the long-range repulsion.