Dr. Markus Lackinger
Technical University of Munich, Germany
Markus Lackinger leads a research group at the Deutsches Museum in Munich, Germany. He studied physical engineering at the University of Applied Sciences in Munich and received his Ph.D. in experimental physics from Chemnitz University of Technology in 2003. He then did a Postdoc with Prof. Wilson Ho at the University of California, Irvine. In 2006 he became a research group leader and later on substitute professor at the Ludwig-Maximilians-University Munich. On-surface synthesis with a special focus on 2D polymers and the thorough characterization of their structures and properties is now his main research goal.
Talk title: On the utility of spectroscopy for on-surface synthesis
Scanning Probe Microscopy is the valued analytical tool of on-surface synthesis, providing submolecular views of reactants, products and sometimes intermediates. However, relevant aspects such as subtle chemical changes and structural details remain inaccessible. In addition, direct monitoring of reaction progress in real time is challenging. This analytical gap can be filled by complementary spectroscopies as highlighted in this presentation:
(1) Typically, reactions are verified in the chemical core level shifts of the atoms involved as measured by X-ray Photoelectron Spectroscopy (XPS). Occasionally, however, the shifts are too small or the peaks are obscured by a large background. Cycloadditions are an example where surface sensitive IR spectroscopy facilitates the verification of the coupling reaction.1
(2) On-surface synthesis relies on the chemically active role of metal surfaces. However, structural and electronic properties are strongly influenced by adsorption on these surfaces. The extent of the surface influence can be assessed from accurately measured adsorption heights. Using X-ray Standing Wave analysis, we show that decoupling by intercalation of an iodine monolayer between the organic nanostructures and the metal surface not only significantly increases the adsorption height, but also identifies structural relaxations indicative of weakened molecule-surface interactions.2
(3) Reaction kinetics can be monitored by real-time XPS, allowing, at least in principle, the quantification of kinetic reaction parameters such as the pre-exponential and the activation energy.3 Ideally, mechanistic insights are also gained from the measured kinetics. Using debromination on Ag(111) as a model reaction, we show that fitting is ambiguous.4,5 Interestingly, improved fits are obtained by assuming a second-order rate law, which implies an additional reactant for debromination. This is supported by DFT calculations indicating a significantly lower activation energy or Ag adatom assisted debromination.4
References:
1 Nat. Chem. 13, 730-736 (2021), https://doi.org/10.1038/s41557-021-00709-y
2 Nanoscale Horiz. 7, 51-62 (2022), https://doi.org/10.1039/D1NH00486G
3 J. Am. Chem. 141, 4824–4832 (2019), https://doi.org/10.1021/jacs.8b11473
4 Nanoscale, in press (2024), https://doi.org/10.1039/D4NR00468J
5 ChemPhysChem, in press (2024), https://doi.org/10.1002/cphc.202400156
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