Stabilization of bimolecular islands on ultrathin NaCl films by a vicinal substrate

Abstract

a b s t r a c tThe structure of ultrathin NaCl films on Au(1 1 1) and on Au(11 12 12), as well as the one of bimolecular 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) and 1,4-bis-(2,4-diamino-1,3,5,-triazine)-benzene (BDATB) islands on NaCl films on both surfaces have been studied with a low-temperature scanning tunnelling microscope. We show that intermixed bimolecular assemblies based on selective three-fold hydrogen-bonding (H-bonding), that have previously been observed on Au(1 1 1) and on Au(11 12 12), can also be stabilized on insulating NaCl films on Au, however, only if these films are grown on Au(11 12 12) and not on Au(1 1 1). The behaviour of the heterocomplex structures is found to be largely influenced by the structural properties of the underlying substrate and by the number of NaCl layers. On a partly NaCl-covered Au(1 1 1) surface, the excess of molecules after completion of the first layer on Au prefers to form a second molecular layer based on ordered heterocomplex structures rather than to adsorb on the NaCl islands. The use of a vicinal surface together with the strong cohesion characteristic of the NaCl film introduces smooth elastic deformations on the NaCl(0 0 1) plane. As a consequence, the periodically modified structure of the overlayer provides preferential binding sites and allows adsorption of two-dimensional molecular structures. In contrast to what is observed on Au(11 12 12), the molecular domains on the NaCl film do not follow the Au step directions, but the NaCl(0 0 1) high symmetry directions. Our results provide a strategy to increase the adsorption energy of flat molecules on insulating layers by choosing a vicinal metal substrate.

Growth and characterization of fullerene nanocrystals on NaCl/Au(111)

“…In this case, owing to a subtle balance of surface energies and dewetting phenomena [19][20][21] , the fullerene molecules grow in a threedimensional (3D) fashion and form nanocrystals. Similar results have been obtained for other molecules such as bimolecular perylenetetracarboxylic diimide (PTCDI) and BDATB on NaCl on vicinal Au surfaces 22 . On the other hand, for porphyrines the formation of 2D ordered epitaxial molecular monolayers on NaCl has been observed 23 , which was attributed to a decreasing van der Waals interaction with increasing number of alkali halide layers and additional charge transfer to the underlying Ag(001) metal substrate.…”

“…This non-linearity of the apparent height of NaCl multilayers with the number of layers is typical for insulating films and originates from the difference of the apparent tunneling barrier formed by NaCl layers of different thickness 36,37 . Note that the values of the apparent height may differ substantially depending on the tip state or the bias voltage used for scanning 22,38 . Table I summarizes the measured apparent heights observed for the investigated systems in the present study.…”

Resolving all atoms of an alkali halide via nanomodulation of the thin NaCl film surface using the Au(111) reconstruction

“…NaCl/Au(111) interface state When deposited on a clean Au(111) surface at room temperature, NaCl forms bilayered (100)-terminated islands with perfect nonpolar step edges. 9,14 Figure 1(a) illustrates the carpetlike growth of NaCl islands over the steps of the Au(111) surface. The Au(111) herringbone reconstruction is not influenced by the NaCl islands and its corrugation is the same on NaCl/Au(111) as on the bare Au(111).…”

Coulomb blockade phenomena observed in supported metallic nanoislands

“…Studies of NaCl layers on other substrates abound, e.g., on Al(111) (35, 38), on Cu(111) (39), on Ag(100) (36,40,41), and on Au(111) (42)(43)(44). NaCl(100) layers are very versatile as a dielectric ultrathin film for the electronic decoupling of supported molecules (39,42,43) or other nanostructures (27) from a metallic substrate.…”