Abstract

Controlling supramolecular self-assembly is a fundamental step towards molecular
nanofabrication, which involves a formidable reverse engineering problem. It is known that
a variety of structures are efficiently obtained by assembling appropriate organic molecules
and transition metal atoms on well-defined substrates. Here we show that alkali atoms bring
in new functionalities compared with transition metal atoms because of the interplay of local
chemical bonding and long-range forces. Using atomic-resolution microscopy and theoretical
modelling, we investigate the assembly of alkali (Cs) and transition metals (Mn) co-adsorbed
with 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules, forming chiral superstructures
on Ag(100). Whereas Mn-TCNQ4 domains are achiral, Cs-TCNQ4 forms chiral islands. The
specific behaviour is traced back to the different nature of the Cs- and Mn-TCNQ bonding,
opening a novel route for the chiral design of supramolecular architectures. Moreover, alkali
atoms provide a means to modify the adlayer electrostatic properties, which is important for
the design of metal–organic interfaces.