arXiv subjects

Frank Müller

Publications and source records attributed to Frank Müller.

9 recordsLinked to original sources

arXiv2024

Impact of geometry on chemical analysis exemplified for photoelectron spectroscopy of black silicon

For smooth surfaces, chemical composition can be readily analyzed using various spectroscopic techniques, a prominent example is X-ray photoelectron spectroscopy (XPS), where the relative proportions of the elements are mainly determined by the intensity ratio of the element-specific photoelectrons. However, this analysis becomes more complex for nanorough surfaces like black silicon (b-Si) due to the geometry's steep slopes, which mimic local variations in emission angles. In this study, we explicitly quantify this effect through an integral geometric analysis using Minkowski tensors, correlating XPS chemical data with topographical information from Atomic Force Microscopy (AFM). This approach yields reliable estimates of layer thicknesses for nanorough surfaces. For b-Si, we found that the oxide layer is approximately 50% thicker than the native oxide layer on a standard Si wafer. This study underscores the significant impact of nanoscale geometries on chemical property analysis.

cond-mat.mes-hall↗

arXiv2020

Projectability of stable, partially free $H$-surfaces in the non-perpendicular case

A projectability result is proved for surfaces of prescribed mean curvature (shortly called $H$-surfaces) spanned in a partially free boundary configuration. Hereby, the $H$-surface is allowed to meet the support surface along its free trace non-perpendicularly. The main result generalizes known theorems due to Hildebrandt-Sauvigny and the author himself and is in the spirit of the well known projectability theorems due to Radó and Kneser. A uniqueness and an existence result are included as corollaries.

math.DG↗

arXiv2020

Optimal $C^{1,\frac{1}{2}}$-regularity of $H$-surfaces with a free boundary

We prove that a surface of prescribed mean curvature ($H$-surface) with free boundary on a two-dimensional $C^2$-manifold belongs to $C^{1,\frac{1}{2}}$ up to that the boundary, provided it is a-priori continuous. We allow the $H$-surface to meet the manifold non-perpendicularly and the manifold itself to have a boundary. Our result is optimal according to an example of Hildebrandt and Nitsche.

math.AP↗

arXiv2017

Unwanted electroless zinc plating on current collectors in zinc air batteries

The occurrence of metallic film deposition without external power supply on the copper current collector of a zinc air battery half-cell containing zinc slurry is investigated. Therefore, test specimens of miscellaneous materials representing the current collector are immersed in a commercial available zinc slurry as well as an in self-prepared zinc slurry. In case of copper and metals which are more noble (silver and gold), a coating on the respective specimen is obtained. An element mapping of the coated copper specimen is performed by means of scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) identifying that the coating layer consists of zinc and oxygen. In order to clarify the crystal structure and the exact composition, focused ion beam (FIB) and x-ray photoelectron spectroscopy (XPS) measurements are applied, proving that the layer consists of elemental zinc, which, is merely oxidized on the surface. Finally, a reaction mechanism for the reversible zinc film deposition is proposed.

cond-mat.mtrl-sci↗

arXiv2016

Evacuation dynamics of asymmetrically coupled pedestrian pairs

We propose and analyze extended floor field cellular automaton models for evacuation dynamics of inhomogeneous pedestrian pairs which are coupled by asymmetric group interactions. Such pairs consist of a leader, who mainly determines the couple's motion and a follower, who has a defined tendency to follow the leader. Examples for such pairs are mother and child or two siblings of different age. We examine the system properties and compare them to the case of a homogeneous crowd. We find a strong impact on evacuation times for the regime of strong pair coupling due to the occurrence of a clogging phenomenon. In addition we obtain a non-trivial dependence of evacuation times on the followers' coupling to the static floor field, which carries the information of the shortest way to the exit location. In particular we find that systems with fully passive followers, who are solely coupled to their leaders, show lower evacuation times than homogeneous systems where all pedestrians have an equal tendency to move towards the exit. We compare the results of computer simulations with recently performed experiments.

physics.soc-ph↗

arXiv2016

Empirical study of the influence of social groups in evacuation scenarios

The effects of social groups on pedestrian dynamics, especially in evacuation scenarios, have attracted some interest recently. However, due to the lack of reliable empirical data, most of the studies focussed on modelling aspects. It was shown that social groups can have a considerable effect, e.g. on evacuation times. In order to test the model predictions we have performed laboratory experiments of evacuations with different types and sizes of the social groups. The experiments have been performed with pupils of different ages. Parameters that have been considered are (1) group size, (2) strength of intra-group interactions, and (3) composition of the groups (young adults, children, and mixtures). For all the experiments high-quality trajectories for all participants have been obtained using the PeTrack software. This allows for a detailed analysis of the group effects. One surprising observation is a decrease of the evacuation time with increasing group size.

physics.soc-ph↗

arXiv2012

Is adhesion superficial? Silicon wafers as a model system to study van der Waals interactions

Adhesion is a key issue for researchers of various fields, it is therefore of uppermost importance to understand the parameters that are involved. Commonly, only surface parameters are employed to determine the adhesive forces between materials. Yet, van der Waals forces act not only between atoms in the vicinity of the surface, but also between atoms in the bulk material. In this review, we describe the principles of van der Waals interactions and outline experimental and theoretical studies investigating the influence of the subsurface material on adhesion. In addition, we present a collection of data indicating that silicon wafers with native oxide layers are a good model substrate to study van der Waals interactions with coated materials.

cond-mat.mtrl-sci↗

arXiv2010

The order parameter of high temperature superconductors, as measured by Andreev Saint-James reflection, Raman and neutron scattering

By comparing experiments that use Andreev Saint-James reflection, Raman scattering (B2g) and neutron scattering on the (cuprate) high temperature superconductors, evidence is found, that all of the techniques can measure the order parameter of these superconductors. The order parameter is the energy needed to take a superconducting boson out of the condensate. It has the same temperature and doping dependence as the superconducting transition temperature Tc. This condensation energy is different from the pairing energy (as measured by the pseudogap) except for the doping x = 0.27, where the two energies coincide: this latter situation represents the BCS case, which in the view presented here is a special case in the BCS-BEC cross-over situation appropriate for the (cuprate) high temperature superconductors.

cond-mat.supr-con↗

arXiv2008

Boundary regularity via Uhlenbeck-Rivière decomposition

We prove that weak solutions of systems with skew-symmetric structure, which possess a continuous boundary trace, have to be continuous up to the boundary. This applies, e.g., to the H-surface system with bounded H and thus extends an earlier result by P. Strzelecki and proves the natural counterpart of a conjecture by E. Heinz. Methodically, we use estimates below natural exponents of integrability and a recent decomposition result by T.Rivière.

math.AP↗