arXiv subjects

Alexander Reichmann

Publications and source records attributed to Alexander Reichmann.

4 recordsLinked to original sources

arXiv2025

Towards predictive atomistic simulations of SiC crystal growth

Simulations of SiC crystal growth using molecular dynamics (MD) have become popular in recent years. They, however, simulate very fast deposition rates, to reduce computational costs. Therefore, they are more akin to surface sputtering, leading to abnormal growth effects, including thick amorphous layers and large defect densities. A recently developed method, called the minimum energy atomic deposition (MEAD), tries to overcome this problem by depositing the atoms directly at the minimum energy positions, increasing the time scale. We apply the MEAD method to simulate SiC crystal growth on stepped C-terminated 4H substrates with 4{\deg} and 8{\deg} off-cut angle. We explore relevant calculations settings, such as amount of equilibration steps between depositions and influence of simulation cell sizes and bench mark different interatomic potentials. The carefully calibrated methodology is able to replicate the stable step-flow growth, which was so far not possible using conventional MD simulations. Furthermore, the simulated crystals are evaluated in terms of their dislocations, surface roughness and atom mobility. Our methodology paves the way for future high fidelity investigations of surface phenomena in crystal growth.

cond-mat.mtrl-sci↗

arXiv2025

Multi-Orbital Charge Transfer into Nonplanar Cycloarenes Revealed with CO-Functionalized Tips

On-surface synthesis has allowed for the tuneable preparation of numerous molecular systems with variable properties. Recently, we demonstrated the highly selective synthesis of kekulene (>99%) on Cu(111) and isokekulene (92%) on Cu(110) from the same molecular precursor (Ruan et al., Angew. Chem. Int. Ed. 2025, e202509932). Scanning tunneling microscopy with CO-functionalized tips can identify the single molecules on the basis of their geometric structure at a low coverage on Cu(110), but it also detects complex features due to electronic contributions close to the Fermi energy. Here, we investigate the origin of these features by simulating STM images based on a weighted sum of multiple molecular orbitals, for which we employ weights based on the calculated molecular-orbital projected density of states. This allows for an experimental confirmation of charge transfer from the surface into multiple formerly unoccupied molecular orbitals for single molecules of kekulene as well as isokekulene in its two nonplanar adsorption configurations. In comparison, the area-integrating photoemission orbital tomography technique confirms the charge transfer as well as the high selectivity for the formation of a full monolayer of mainly isokekulene on Cu(110). Our STM-based approach is applicable to a wide range of adsorbed molecular systems and specifically also suited for strongly interacting surfaces, nonplanar molecules, and such molecules which can only be prepared at extremely low yields.

physics.chem-ph↗

arXiv2025

Interstitials as a key ingredient for P segregation to grain boundaries in polycrystalline $\alpha$-Fe

Solute segregation to grain boundaries (GBs) significantly impacts material behavior, with most studies focusing on substitutional solute segregation while neglecting interstitial segregation due to its increased complexity. The site preference, interstitial or substitutional, for P segregation in $\alpha$-Fe still remains under debate. This work investigates both substitutional and interstitial GB segregation in a polycrystalline model using classical interatomic potentials and machine learning. The method is validated with H and Ni, whose segregation behaviors are well understood. For P, we find segregation to both GB site types, with a preference for substitutional sites based on mean segregation energy. However, the abundance of interstitial sites means interstitial segregation also significantly contributes to the GB enrichment with P. This highlights the importance of considering interstitial P segregation alongside substitutional segregation. Additionally, obtaining a representative spectrum of segregation energies is crucial for accurate, experimentally aligned predictions.

cond-mat.mtrl-sci↗

arXiv2022

On Strong-Scaling and Open-Source Tools for High-Throughput Quantification of Material Point Cloud Data: Composition Gradients, Microstructural Object Reconstruction, and Spatial Correlations

Characterizing microstructure-material-property relations calls for software tools which extract point-cloud- and continuum-scale-based representations of microstructural objects. Application examples include atom probe, electron, and computational microscopy experiments. Mapping between atomic- and continuum-scale representations of microstructural objects results often in representations which are sensitive to parameterization; however assessing this sensitivity is a tedious task in practice. Here, we show how combining methods from computational geometry, collision analyses, and graph analytics yield software tools for automated analyses of point cloud data for reconstruction of three-dimensional objects, characterization of composition profiles, and extraction of multi-parameter correlations via evaluating graph-based relations between sets of meshed objects. Implemented for point clouds with mark data, we discuss use cases in atom probe microscopy that focus on interfaces, precipitates, and coprecipitation phenomena observed in different alloys. The methods are expandable for spatio-temporal analyses of grain fragmentation, crystal growth, or precipitation.

cond-mat.mtrl-sci↗