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SummaryWe present an overview of experimental and numerical methods to determine the spring constant of a quartz tuning fork in qPlus configuration. The simple calculation for a rectangular cantilever is compared to the values obtained by the analysis of the thermal excitation and by the direct mechanical measurement of the force versus displacement. To elucidate the difference, numerical simulations were performed taking account of the real geometry including the glue that is used to mount the tuning fork.

Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of 47048 Duisburg, Germany (Received 27 March 2013; accepted 29 May 2013; published online 7 June 2013) Individual molecules of octa-ethyl-porhphyrin-iron(III)-chloride adsorbed on a Cu(111) surface are studied by scanning tunneling microscopy. Upon moderate heating the molecules are found to transform into Fe-tetra-benzo-porphyrin at a surprisingly low temperature of 380 K. If the annealing is interrupted, the different steps of the transformation can be imaged. By evaluating the ratio of transformed molecules as function of annealing temperature, an approximate activation energy of 1.2 eV ± 0.1 eV could be determined. © 2013 AIP Publishing LLC.

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To be or not to be chlorinated: When octaethylporphyrin iron(III) chloride (FeOEPCl) molecules are sublimated onto Cu(111) surfaces, two different molecular species are observed through scanning tunneling microscopy, showing either a protrusion or a depression at the center. In combination with van der Waals‐corrected density functional calculations, our experiments reveal that one species corresponds to FeOEPCl molecules with the chlorine atom pointing away from the surface, whereas the other species has been dechlorinated.