From Au-Thiolate Chains to Thioether Sierpiński Triangles: The Versatile Surface Chemistry of 1,3,5-Tris(4-Mercaptophenyl)Benzene on Au(111)

Self-assembly of 1,3,5-tris(4-mercaptophenyl)benzene (TMB) – a three-fold symmetric, thiol functionalized aromatic molecule – was studied on Au(111) with the aim to realize extended Au-thiolate linked molecular architectures. The focus lay on resolving thermally activated structural and chemical changes by a combination of microscopy and spectroscopy. Thereby Scanning Tunneling Microscopy provided submolecularly resolved structural information, while the chemical state of sulfur was assessed by X-ray Photoelectron Spectroscopy. Directly after room temperature deposition only less well ordered structures were observed. Mild annealing promoted the first structural transition into ordered molecular chains, partly organized in homochiral molecular braids. Further annealing led to self-similar Sierpiński triangles, while annealing at even higher temperatures again resulted in mostly disordered structures. Both the irregular aggregates observed at room temperature and the chains were identified as metal-organic assemblies, whereby two out of the three intermolecular binding motifs are energetically equivalent according to Density Functional Theory simulations. The emergence of Sierpiński triangles is driven by a chemical transformation, i.e. the conversion of coordinative Au-thiolate to covalent thioether linkages, and can be further understood by Monte Carlo simulations. The great structural variance of TMB on Au(111) can on one hand be explained by the energetic equivalence of two binding motifs. On the other hand, the unexpected chemical transition even enhances the structural variance and results in thiol-derived covalent molecular architectures

Real time investigations during sputter deposition for tailoring optical properties of metal-polymer interfaces

Poster presented at the 16th International Conference on Small-Angle Scattering, held on 13-18th September, 2015, Berlin (Germany).Tailoring optoelectronic properties of metal-polymer interfaces using self-assembly of nanoparticles is of crucial importance in organic electronics and organic photovoltaics [1]. In particular, metal sputter deposition on block-co-polymers is one widely used method to fabricate nanostructured metal layers on a large scale exploiting the selective wetting and doping of metals on polystyrene domains [2,3]. In order to obtain full control over the nanostructural evolution at the metal-polymer interface and its impact on optoelectronic properties, we employed a combination of in situ time-resolved microfocus Grazing Incidence Small Angle X-ray Scattering (μGISAXS) with in situ UV/Vis Specular Reflectance Spectroscopy (SRS) during sputter deposition of gold (Au) on thin polystyrene films (PS). We monitored the evolution of the metallic layer morphology according to changes in the key scattering features by geometrical modeling [4] and correlate the nanostructural development to optical properties. The changes of optoelectronic properties induced by metal nanoparticle growth during the sputter deposition process were exemplarily monitored using SRS. The morphological characterization is complemented by X-ray reflectivity and electron microscopy. This enables us to identify the different growth regimes including their specific thresholds and permits better understanding of the growth kinetics of gold clusters and their self-organization into complex nanostructures on polymer substrates. Thus, our findings are of great interest for applications in organic photovoltaics [5] and organic electronics, which benefit from tailored metal-polymer interfaces

Microstructural and plasmonic modifications in Ag-TiO₂ and Au-TiO₂ nanocomposites through ion beam irradiation

The development of new fabrication techniques of plasmonic nanocomposites with specific properties is an ongoing issue in the plasmonic and nanophotonics community. In this paper we report detailed investigations on the modifications of the microstructural and plasmonic properties of metal–titania nanocomposite films induced by swift heavy ions. Au–TiO2 and Ag–TiO2 nanocomposite thin films with varying metal volume fractions were deposited by co-sputtering and were subsequently irradiated by 100 MeV Ag8+ ions at various ion fluences. The morphology of these nanocomposite thin films before and after ion beam irradiation has been investigated in detail by transmission electron microscopy studies, which showed interesting changes in the titania matrix. Additionally, interesting modifications in the plasmonic absorption behavior for both Au–TiO2 and Ag–TiO2 nanocomposites were observed, which have been discussed in terms of ion beam induced growth of nanoparticles and structural modifications in the titania matrix

Coexistence of one- and two-dimensional supramolecular assemblies of terephthalic acid on Pd(111) due to self-limiting deprotonation

The adsorption of terephthalic acid [C6H4(COOH)(2), TPA] on a Pd(111) surface has been investigated by means of scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy, and near-edge x-ray absorption fine structure spectroscopy under ultrahigh vacuum conditions at room temperature. We find the coexistence of one- (1D) and two-dimensional (2D) molecular ordering. Our analysis indicates that the 1D phase consists of intact TPA chains stabilized by a dimerization of the self-complementary carboxyl groups, whereas in the 2D phase, consisting of deprotonated entities, the molecules form lateral ionic hydrogen bonds. The supramolecular growth dynamics and the resulting structures are explained by a self-limiting deprotonation process mediated by the catalytic activity of the Pd surface. Our models for the molecular ordering are supported by molecular mechanics calculations and a simulation of high resolution STM images