Effect of lattice-gas atoms on the adsorption behaviour of thioether molecules

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Using STM topographic imaging and spectroscopy, we have investigated the adsorption of two thioether molecules, 1,2-bis(phenylthio)benzene and (bis(3-phenylthio)-phenyl)sulfane, on noble and transition metal surfaces. The two substrates show nearly antipodal behaviour. Whereas complexes with one or two protruding centres are observed on Au(111), only flat and uniform ad-structures are found on NiAl(110). The difference is ascribed to the possibility of the thioethers to form metal–organic complexes by coordinating lattice-gas atoms on the Au(111), while only the pristine molecules adsorb on the alloy surface. The metal coordination in the first case is driven by the formation of strong Au–S bonds and enables the formation of characteristic monomer, dimer and chain-like structures of the thioethers, using the Au atoms as linkers. A similar mechanism is not available on the NiAl, because no lattice gas develops at this surface at room temperature. Our work demonstrates how surface properties, i.e. the availability of mobile ad-species, determine the interaction of organic molecules with metallic substrates.DFG, EXC 314, Unifying Concepts in Catalysi

Adsorption of thioether molecules on an alumina thin film

Low-temperature scanning tunneling microscopy has been employed to study the adsorption of (bis(3-phenylthio)-phenyl)sulfane (BPPS) molecules on an aluminum-oxide film grown on NiAl(110). Large variations in the molecular coverage on incompletely oxidized samples indicate substantial differences in the binding strength of BPPS to metallic (NiAl) versus dielectric (alumina) surfaces. From atomically resolved images, we obtain possible BPPS adsorption geometries on the oxide, in which the sulfur centers and not the phenyl rings of the molecule govern the interaction. A local hexagonal ordering of BPPS, as deduced from pair correlation functions, suggests a preferential binding of the BPPS sulfur atoms to Al ions with distorted pyramidal coordination in the oxide surface. Our work provides insight into rarely explored binding schemes of organic molecules on wide-gap oxide materials. (C) 2014 Elsevier B.V. All rights reserved

Growth of Two-Dimensional Lithium Islands on CaO(001) Thin Films

The nucleation and growth behavior of lithium on a CaO/Mo(001) thin film has been investigated by means of scanning tunneling microscopy and spectroscopy. The Li follows two different growth regimes on the surface. Whereas extended 2D islands develop on top of the defect-free CaO terraces, small 3D deposits decorate a network of domain boundaries that is present in the oxide film. The 2D islands have metallic character, as deduced from a standing wave pattern observed on their surface at low-bias. In contrast, a cationic nature is proposed for the defect-bound 30 species as a result of an electron-transfer from the Li 2s valence orbital into trap states localized in the CaO line defects. Tunneling spectroscopy reveals an unoccupied gap state below the CaO conduction band that originates from Li-O hybridization across the metal-oxide interface. With increasing diameter of the Li islands, this state shifts toward the Fermi level, reflecting the decreasing workfunction at higher Li coverage