Femtosecond time resolution for the local investigation of surface processes
Final Report Abstract
This project investigated the dependence of thermal and laser induced diffusion on low-indexed coin metal surfaces (and one surface alloy) on several factors via low temperature scanning tunneling microscopy. In order to determine energy barriers, the STM was first optimized and calibrated to facilitate measurements at different temperatures. A thermal precision 0.2 K allowed us to perform thermal diffusion measurements with high fidelity. Furthermore, apparent height spectroscopy was improved, for the identification of the diffusing species. Employing these methods revealed that the presence of other molecules influence the diffusion of CO on Cu(111), by the long-range interaction mediated through the surface electrons, surprisingly with a phase shift of this interaction between thermal and laser-induced diffusion. The wave length of the oscillation of the diffusion energy thereby depends on the local CO coverage. Moreover, there exist cooperative effects, such that the three-body interaction exceeds the sum of the corresponding pair interactions. Direct interaction between CO leads to the formation of CO dimers with an influence on diffusion that largely exceeds the influence of the indirect interaction. In particular on Ag(100), the diffusion barrier of the dimer is considerably smaller than the one of the monomer due to a qualitatively different motion, based on rotation. A combination of rotation with diffusion should not only be relevant for molecular dimers, but also for larger molecules that could thus follow a low energy diffusion path that is not available at pure translation. Such a low energy diffusion path was confirmed for the Diffusion of Co-phtalocyanines, likewise on Ag(100), as confirmed by ab initio calculations. The project revealed the influence of several interactions on diffusion order realistic, i.e. crowded conditions, pointing out that diffusion during heterogeneous catalysis can hardly be deduced from single molecule behavior.
Publications
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(2018) Understanding the Enhancement of Surface Diffusivity by Dimerization. Physical review letters 121 (18) 185901
Zaum, C.; Morgenstern, K.
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Complex surface diffusion mechanisms of cobalt phthalocyanine molecules on Ag(100). J. Am. Chem. Soc. 137 (2015) 14920 - 14929
Grazyna Antczak, Wojciech Kamiński, Agata Sabik, Christopher Zaum, Karina Morgenstern
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Dependence of alloying and island composition on terrace width. Phys. Rev. B 92 (2015) 045422 - 1-6
Agnes Beichert, Christopher Zaum, Karina Morgenstern
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Differences between adiabatic and non-adiabatic diffusion. Phys. Rev. Lett. 114 (2015) 146104
Christopher Zaum, Kastur M. Meyer-auf-der-Heide, Michael Mehlhorn, Steve McDonough, William F. Schneider, Karina Morgenstern
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Nano Lett Experimental evidence for a three-body interaction between diffusing CO molecules. Nano Letters 16 (2016) 3001
Christopher Zaum, Karina Morgenstern
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Temperature calibration for diffusion experiments to sub-Kelvin precision. Rev. Sci. Instr. 87 (2016) 053902
Christopher Zaum, Cord Bertram, Kastur M. Meyer auf der Heide, Michael Mehlhorn, Karina Morgenstern
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Local modification of the surface state properties at dilute coverages: CO/Cu(111). Phys. Rev. B, 97, 155437 (2018)
Christopher Zaum, Kastur M. Meyer-auf-der-Heide, Karina Morgenstern
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Voltage dependent STM imaging of anorganic adsorbates. Appl. Phys. Lett. 113, 031602 (2018)
Christopher Zaum, Karina Morgenstern
