Recent Results
Atomic force microscopy reveals bistable configurations of dibenzo[a,h]thianthrene and their interconversion pathway
Niko Pavliček, Benoit Fleury, Mathias Neu, Judith Niedenführ, Coral Herranz-Lancho, Mario Ruben, and Jascha Repp
We have visualized a difference in the chemical structure of two molecular configurations of dibenzo[a,h]thianthrene (DBTH) molecules by means of atomic force microscopy.
Recently, Gross et al. (Science, 2009) have demonstrated the role of tip-functionalization in atomic force microscopy by resolving the chemical structure of pentacene molecules. Shortly after, this technique was used to identify the structure of an organic molecule. In this paper, we have investigated DBTH molecules adsorbed on NaCl layers in a combined scanning tunneling and atomic force microscopy (STM/AFM) study. DBTH molecules are derivates of the butterfly-shaped thianthrene molecule, in which the wings are extended by one benzene ring. By inelastic current excitations in STM mode, we can switch the wings between pointing up or down. The positions of the wings, however, could only be revealed in the AFM mode. The atomically resolved AFM images also reveal that the butterfly is flapping its wings as opposed to turning upside down.
Physical Review Letters 108, 086101 (2012).
Video of 4NCuPc trimer formation on NaCl/Cu(111)
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Controlled Lateral Manipulation of Molecules on Insulating films
Video of 4NCuPc trimer formation on NaCl/Cu(111)
Direct links: MP4 format | Ogg format | WebM format
Ingmar Swart, Tobias Sonnleitner, Judith Niedenführ, and Jascha Repp
It has been demonstrated that the tip of a scanning tunneling microscope/atomic force microscope can be used to build nanostructures with atomic scale position on metallic and semiconductor surfaces. In contrast, controlled lateral manipulation on insulators had not been reported. We demonstrated that molecules adsorbed on ultrathin insulating films can be laterally manipulated in a controlled way by injecting inelastically tunneling electrons at well-defined positions in a molecule. This technique was found to be applicable to several different molecules.
Molecular Symmetry Governs Surface Diffusion
Tobias Sonnleitner, Ingmar Swart, Niko Pavliček, Andreas Pöllmann, and Jascha Repp
In many areas of chemistry and physics the symmetry of an object or process plays a decisive role. One prominent example is the selection rules governing optical transitions. We investigated the influence of molecular symmetry on the surface potential landscape. For this purpose, the nonthermal diffusion induced by inelastic excitations of a molecule, for which four symmetry distinct isomers exist, was studied. The observed nonthermal diffusion was found to be qualitatively different for all four symmetry distinct isomers. This demonstrates that adsorbate symmetry plays an important role in determining the surface potential landscape.
Phys. Rev. Lett. 107, 186103 (2011).
Controlling the charge state of single molecules: visualizing changes in the tunneling barrier with submolecular resolution
Ingmar Swart, Tobias Sonnleitner, and Jascha Repp
The tip of a scanning tunneling microscope was used to controllably add and remove an additional electron to and from a single molecule. It is shown that charge-state control of individual molecules adsorbed on surfaces can be obtained by choosing a substrate system with an appropriate workfunction. By subtracting images of molecules in the neutral and anionic charge state, information regarding the spatial distribution of the additional charge was obtained. These difference images show marked intramolecular contrast.
Imaging Bond Formation Between Gold and Pentacene on an Insulating Surface
Jascha Repp, Gerhard Meyer, Sami Paavilainen, Fredrik E. Olsson, Mats Persson
A covalent bond between an individual pentacene molecule and a gold atom is formed by means of single-molecule chemistry inside a scanning tunneling microscope junction. The bond formation is reversible, and different structural isomers can be produced. The single-molecule synthesis is done on ultrathin insulating films that electronically isolate the reactants and products from their environment. Direct imaging of the orbital hybridization upon bond formation provides insight into the energetic shifts and occupation of the molecular resonances.
Scanning Tunneling Microscopy Imaging of Individual Molecular Orbitals
Jascha Repp, Gerhard Meyer, Sladjana M. Stojkovic, Andre Gourdon, Christian Joachim
Ultrathin insulating NaCl films have been employed to decouple individual pentacene molecules electronically from the metallic substrate. This allows the inherent electronic structure of the free molecule to be preserved and studied by means of low-temperature scanning-tunneling microscopy. Thereby direct images of the unperturbed molecular orbitals of the individual pentacene molecules are obtained. Elastic scattering quantum chemistry calculations substantiate the experimental findings.
Phys. Rev. Lett. 94, 026803 (2005).
Controlling the Charge State of Individual Gold Adatoms
Jascha Repp, Gerhard Meyer, Fredrik E. Olsson, Mats Persson
The nature and control of individual metal atoms on insulators are of great importance in emerging atomic-scale technologies. Individual gold atoms on an ultrathin insulating sodium chloride film supported by a copper surface exhibit two different charge states, that are stabilized by the large ionic polarizability of the film. The charge state and associated physical and chemical properties such as diffusion can be controlled by adding or removing a single electron to or from the adatom with a scanning tunneling microscope tip.