Department of Physics • University of Cologne

The talk will cover spectroscopic investigations on the catalytic properties of iron nanoparticle arrays and details on the formation of nanographene in nano-heterostructures. The increased complexity of real-life catalysts as compared to surface science leads to the “materials gap”. To close this gap, studies of adsorption and reaction experiments on nanoparticles supported on 2D materials were conducted under in situ conditions with the particular aim to elucidate the reactivity of such more “realistic” nanoparticles. It is shown that the use of a quantitative spectroscopy allows for gaining a detailed insight even to these complex systems, thereby facilitating a further step into bridging the materials gap from fundamental science to applied sciences. The use of the 2D materials as a chemically “innocent” substrate gives the intriguing possibility to study the system without the additional influence of side processes such as spill over and reverse spill over. Such studies allow for characterization of novel cluster systems towards their reactivity and adsorption behavior, e.g. for iron nanoclusters with the probe molecule CO. Such reactivity studies are also possible for the more complex chemistry of ethylene on Pt nanoclusters where detailed insights to the reaction pathway become available. Thereby the changes when going from single crystals to nanoclusters become evident. As a second topic, the formation of van-der-Waals nano-heterostructures is discussed. Insights from spectroscopic and microscopic studies allowed us to characterize the individual preparation steps and the final nano-heterostructure consisting of graphene / metal / h-BN stack. Experiments with different cluster sizes are shown to obtain insights to the pore filling of the h-BN substrate. This gives a direct measure of the agglomeration of the nanoclusters during preparation. Literature F. Düll, et al. ACS Applied Nano Materials 2 (2019) 7019. F. Düll, et al. Journal of Chemical Physics 152 (2020) 224710. F. Düll, et al. Physical Chemistry Chemical Physics 21 (2019) 21287.

In this presentation, the emergence of localised, stable wave packets (solitons) is investigated in the context of the repulsive one-dimensional Bose gas. In the weakly interacting limit, the gas is approximated by the classical non-linear Schrödinger equation, of which it is known that such classical localisation occurs. A natural question to ask would be whether these classical wave packets could be reproduced starting from the quantum non-linear Schrödinger equation, and if so, which quantum mechanical wave function would produce such density profiles. Previous research has indeed attempted to do so, however, these studies had two main limitations: 1) only the attractive regime was investigated, which has limited physical significance because there is no saturation, and 2) localisation was shown only in limiting cases. In the talk, some of the mathematical steps are outlined in an attempt to overcome these two shortcomings. Besides introductory material, the talk is split into three parts according to the results obtained: 1) numerical results are discussed that show whether the desired localisation even exists outside the weakly interacting regime, 2) analytical efforts are discussed that show that Dirichlet kernels arise from the density form factor and finally 3) I will share some of the analytical efforts on simplifying general density form factors, which are of relevance when comparing magnitudes between form factor terms. It is found that mutually repulsive particles experience attraction at the macroscopic level, outside of the weakly and maximally interacting limits.

Superconducting nanowire single-photon detectors (SNSPDs) provide sufficient sensitivity to enable laser induced fluorescence (LIF) experiments in the mid-infrared, an exciting technical development for physical chemistry given the importance of vibrational spectroscopy to molecular science. In this talk, I will describe how an SNSPD works and how to use it. I will also present results of experiments on the vibrational dynamics of monolayers and multilayers of solid CO adsorbed at the surface of a NaCl crystal, to show the capabilities of time-resolved infrared LIF spectroscopy and provide observations of astonishing phenomena arising from dipole-dipole coupling between molecules. In these experiments, a laser light pulse excites about half of the CO to its