Pavel Shukrynau

Site-dependent donation/backdonation charge transfer at the CoPc/Ag(111) interface.

The organic/metal interface formed upon adsorption of cobalt(II) phthalocyanine (CoPc) molecules on a flat Ag(111) single crystal was investigated using a combination of scanning tunneling microscopy (STM) and photoemission spectroscopy (PES). A flat-lying molecular adsorption with the π conjugated phthalocyanine ligand parallel to the substrate was found to lead to an effective molecule-substrate coupling which governs a template-guided molecular growth. A voltage polarity dependence at the cobalt ion site was emphasized and correlated with the Co 2p core level spectra evolution which sustains an interface-confined reduction effect of the cobalt oxidation state. The formation of interface dipoles was observed via monitoring the changes in the work function (WF) upon deposition. The observations are discussed on the basis of a site-dependent donation/backdonation charge transfer at the molecule-substrate interface.

Interplay of hydrogen bonding and molecule–substrate interaction in self-assembled adlayer structures of a hydroxyphenyl-substituted porphyrin

Abstract The formation of hydrogen-bonded organic nano-structures and the role of the substrate lattice thereby were investigated by scanning tunneling microscopy. The self-organization of 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin (H2THPP) molecules leads to two molecular arrangements on Au(111). One of these is characterized by pair-wise hydrogen bonding between hydroxyl groups and a low packing density which enables a rotation of individual molecules in the structure. A different interaction with stronger chain-like hydrogen bonding and additional interactions of phenyl groups was observed for the second structure. The influence of the substrate on the epitaxial behavior is demonstrated by the adsorption of H2THPP on the highly anisotropic Ag(110) substrate. There, several balances between the occupation of favorable adsorption positions and the number of hydrogen bonds per molecule were found. The molecules form molecular chains on Ag(110) and also assemble into two-dimensional periodic arrangements of differently sized close-packed blocks similar to the second type of supramolecular ordering found on Au(111). Dispersion corrected Density Functional Theory calculations were applied to understand the adsorption and complex epitaxy of these molecules. It is shown that the azimuthal orientation of the saddle-shape deformed molecule plays an important role not only for the intermolecular but also for the molecule–substrate interaction.

Manipulation of the electronic structure by reversible dehydrogenation of tetra(p-hydroxyphenyl)porphyrin molecules

Abstract The controlled and reversible interconversion between the free-base and the doubly dehydrogenated form of a 5,10,15,20-tetra( p -hydroxyphenyl)porphyrin molecule in an ordered array is demonstrated. This is achieved through voltage pulses by hydrogen transfer between the center of the porphyrin and the tip of a scanning tunneling microscope (STM). The local dehydrogenation leads to significant shifts in the energetic positions of the molecular orbitals. Density functional theory (DFT) calculations corroborate our conclusions and allow to gain more insight into the different energy level alignments before and after dehydrogenation. Due to the different conductance at a given voltage a clear distinction of both molecular species is possible, which also enables the application as a single-molecular switch.

Investigation of Ultrathin Layers of Bis(phthalocyaninato)lutetium(III) on Graphite

We present a comprehensive study of the adsorption of bis(phthalocyaninato)lutetium(III) (LuPc2) on highly oriented pyrolytic graphite(0001) (HOPG). The growth and self-assembly of the molecular layers as well as the electronic structure has been investigated systematically using scanning tunneling microscopy and scanning tunneling spectroscopy combined with density functional theory (DFT) calculations and molecular mechanics simulations. We reveal that the adsorption of LuPc2 leads to the formation of a square-like close-packed structure on the almost inert surface of HOPG, which is corroborated by simulations. Moreover, we observed a parallel orientation of the LuPc2 molecules in the first monolayer, whereas in subsequent layers an increasing tilt out of the surface plane was found. Tip–sample distance-dependent tunneling spectroscopy measurements allowed us to detect a shift in the energy positions of the peaks assigned to the lowest unoccupied molecular orbital toward the Fermi energy with decreasing ...

Self-Metalation of Phthalocyanine Molecules with Silver Surface Atoms by Adsorption on Ag(110)

We report that metal-free phthalocyanine (H2Pc) molecules with a central cavity are able to incorporate Ag atoms from an Ag(110) surface thus creating silver phthalocyanine (AgPc). The reaction was investigated by means of scanning tunneling microscopy (STM) under ultrahigh vacuum, and the metalation of H2Pc at the interface was confirmed with X-ray photoelectron spectroscopy. Three different kinds of molecules were found on the surface that are assigned to H2Pc, the corresponding dehydrogenated molecules (Pc), and AgPc. The relative amounts of Pc and AgPc increase with increasing annealing temperature. We suggest that the reaction with Ag atoms from the steps of the surface occurs favorably only for already dehydrogenated molecules; thus, the metalation of H2Pc is likely limited by the heat-induced dehydrogenation. Density functional theory simulations of the reaction path are presented to corroborate this hypothesis.

Ordered monolayers of metal-phthalocyanines and rare-earth bisphthalocyanines on crystalline metal substrates - crystallographic and electronic structure

We present investigations on ordered monolayers of various phthalocyanines (CoPc, SnPc, F16CoPc, Lu(Pc)2) adsorbed on Ag(111) and Ag(110) by STM, STS, and PES. The results will help to improve our understanding of the adlayer structure and the electronic structure of the interface to the substrate. Possible applications in nanoelectronics will be discussed.