Bartosz Such Adsorption of carboxyphenyl-substituted Zn porphyrine molecules on TiO2(011). The conference abstract below

Abstract

In the presentation the adsorption and organization of 5-(4-Carboxyphenyl)-10,15,20-triphenylporphyrin-Zn(II) molecules on TiO(011) surface will be described based on the results of scanning tunneling microscope (STM) investigations performed in ultra-high vacuum (UHV). At the coverage below 0.1 monolayer the majority of the molecules are immobilized on the terrace edges and surface defects. While the coverage grows the molecules form linear structure along [01-1] direction, corresponding to the direction of oxygen rows on the (2x1) reconstructed TiO2(011) surface. The molecules remain quite mobile until a full monolayer is formed. The molecules are than adsorbed on the every second reconstruction row thanks to the interaction of the carboxyl groups with the Ti atoms at the surface while their linear assemblies are stabilized by the intermolecular interactions. In contrast to some earlier results it is clear that the molecular board of the porphyrines is far from being perpendicular to the substrate which can have a huge impact on the molecule performance as a sensitizer in a dye-sensitized solar cell.

Res Jöhr, Antoine Hinaut, Rémy Pawlak, Ernst Meyer, Thilo Glatzel, Investigation of adsorption geometries of single Cu-TCPP on rutile TiO2 (110)

Abstract

Molecular adsorbates on surfaces play a major role in many new emerging technologies like hybrid photovoltaics or catalysis. For these applications the adsorption geometry of the molecule is crucial since it influences the electronic properties at the interface, which in turn determines the performance of devices. In many applications like e.g. dye-sensitized solar cells titanium dioxide is widely used as substrate. Hence, the rutile TiO2 (110) structure of titania has become a model system. Due to their tuneability, porphyrins and phthalocyanines are often used as adsorbates. In this study we investigate the adsorption geometry of single copper porphyrins (Cu-TCPP) on rutile TiO2 (110) in UHV. In order to determine the adsorption sites and configuration, we applied non-contact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM) as well as scanning tunnelling microscopy (STM) at low temperature. Different adsorption geometries have been observed with nc-AFM. We find that the molecules lie flat on the surface and do not necessarily bind covalently to the surface. The adsorption geometries were further confirmed by high resolution STM. KPFM measurements reveal a work function difference between the adsorbates and the bare substrate. Particularly we observe that heat treatment of the covered surface leads to a strongly, most probably covalently, bound molecule.

Conference program

We participated at The 5th European Nanomanipulation Workshop in Basel.

Beilstein Journal of Nanotechnology 2013, 4, 927–932.

Abstract

Islands composed of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules are grown on a hydrogen passivated Ge(001):H surface. The islands are studied with room temperature scanning tunneling microscopy and spectroscopy. The spontaneous and tip-induced formation of the top-most layer of the island is presented. Assistance of the scanning probe seems to be one of the factors that facilitate and speed the process of formation of the top-most layer.

Obtaining Detailed Structural Information about Supramolecular Systems on Surfaces by Combining High-Resolution Force Microscopy with ab Initio Calculations

ACS Nano, 2013, 7, 9098-9105.

State-of-the art experimental techniques such as scanning tunneling microscopy have great difficulties in extracting detailed structural information about molecules adsorbed on surfaces. By combining atomic force microscopy and Kelvin probe force microscopy with ab initio calculations, we demonstrate that we can obtain a wealth of detailed structural information about the molecule itself and its environment. Studying an FFPB molecule on a gold surface, we are able to determine its exact location on the surface, the nature of its bonding properties with neighboring molecules that lead to the growth of one-dimensional strips, and the internal torsions and bendings of the molecule. More