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Scanning tunneling microscopy and atomic force microscopy can provide detailed information about the geometric and electronic structure of molecules with submolecular spatial resolution. However, an essential capability to realize the full potential of these techniques for chemical applications is missing from the scanning probe toolbox: chemical recognition of organic molecules. Here, we show that maps of the minima of frequency shift-distance curves extracted from 3D data cubes contain characteristic contrast. A detailed theoretical analysis based on density functional theory and molecular mechanics shows that these features are characteristic for the investigated species. Structurally similar but chemically distinct molecules yield significantly different features. We find that the van der Waals and Pauli interaction, together with the specific adsorption geometry of a given molecule on the surface, accounts for the observed contrast.

Trabajo presentado en el International Workshop On-surface Synthesis, celebrado en San Sebastián del 27 al 30 de junio de 2016., On-surface chemistry has emerged as an important research field leading to unconventional self-assembled nanoarchitectures with tunable properties [1,2]. The development of surfacesensitive spectroscopies has provided a powerful set of tools for a detailed characterization of the structure, composition, and physicochemical properties of the molecular structures obtained by this methodology. We have evaporated p-aminophenol (p-AP) on Cu(110) at 493 K and followed a bottom-up azocoupling reaction, leading to dimer formation: 4,4'-azobis(phenol). We have characterized the on-surface synthesized self-assembled structure by different techniques. Thus, by using a combination of STM/AFM, LEED, XPS and NEXAFS as well as DFT calculations, we are able to unveil the structural and chemical characteristics of the process and outcome. The structural analysis reveals that p-AP molecules have coupled forming new molecular species that self-organize on the surface. They lay in a flat geometry preserving the in-plane ¿- conjugated benzene units as depicted by NEXAFS. LEED pattern analysis shows that the molecular layer exhibit a long-range order with a [(5,1),(-1,2)] symmetry, forming chains rotated 20º with respect to the [001] direction of the Cu surface, as deduced by the STM/AFM images. (Fig 1). Finally, the XPS N1s spectra reveal an oxidation reaction from amine to imine while XPS O1s data suggests that oxygen atoms are covalently bound to the substrate. In summary, all the information obtained by following this multitechnique study, allow us to figure out a model of the structure promoted by the catalytic properties of substrate in a thermal activated process.

We discuss the possibility of a 2D ordered structure formed upon deposition of Si on metal surfaces. We investigate the atomic and electronic structure of the Si-$(\sqrt{19}\times\sqrt{19})R23.4^{\circ}$/Pt(111) surface reconstruction by means of a set of experimental surface-science techniques supported by theoretical calculations. The theory achieves a very good agreement with the experimental results and corroborate beyond any doubt that this phase is a surface alloy consisting of Si$_3$Pt tetramers that resembles a twisted Kagome lattice. These findings render unlikely any formation of silicene or germanene on Pt(111) and other transition metal surfaces., Comment: 5 pages, 4 figures