arXiv subjects

Jiayuwen Qi

Publications and source records attributed to Jiayuwen Qi.

5 recordsLinked to original sources

arXiv2026

Frontiers of atom probe tomography physics, data processing, and analysis

Atom probe tomography (APT) fills a crucial need in the characterization workflow of materials by its ability to inform the 3D chemical microstructure at the nanoscale. As with any characterization techniques, APT has strengths and limitations that inform the interpretation of the data. Therefore, a challenge for the materials characterization community, and the APT community in particular, is the need to establish repeatable and reproducible workflows around the APT data acquisition, reconstruction, analysis, and sharing, in order to inform interpretation. Data interpretation also requires the continued development of our understanding of the physical processes responsible for field evaporation. We review recent developments in the experimental analysis of field evaporation and in the modeling of field evaporation leading to new understanding of common artifacts observed in reconstructed data. We then discuss current challenges with data analysis, translation of results, and data interpretation in the absence of community-agreed standards, and therefore, the crucial need for standardization at every stage of APT research, from data collection all the way to data reporting. This perspective is a summary of the invited presentations and discussions that took place during a workshop (August 4-5, 2024, Alexandria, Virginia, USA).

cond-mat.mtrl-sci↗

arXiv2024

New three-dimensional dispersion in the type-II Dirac semimetals PtTe$_2$ and PdTe$_2$ revealed through Angle Resolved Photoemission Spectroscopy

PtTe$_2$ and PdTe$_2$ are among the first transition metal dichalcogenides that were predicted to host type-II Dirac fermions, exotic particles prohibited in free space. These materials are layered and air-stable, which makes them top candidates for technological applications that take advantage of their anisotropic magnetotransport properties. Here, we provide a detailed characterization of the electronic structure of PtTe$_2$ and PdTe$_2$ using Angle Resolved Photoemission Spectroscopy (ARPES) and Density Functional Theory (DFT) calculations, unveiling a new three-dimensional dispersion in these materials. Through the use of circularly polarized light, we report a different behavior of such dispersion in PdTe$_2$ compared to PtTe$_2$, that we relate to a symmetry analysis of the dipole matrix element. Such analysis reveals a link between the observed circular dichroism and the different momentum-dependent terms in the dispersion of these two compounds, despite their close similarity in crystal structure. Additionally, our data shows a clear difference in the circular dichroic signal for the type-II Dirac cones characteristic of these materials, compared to their topologically protected surface states. Our work provides a useful reference for the ARPES characterization of other transition metal dichalcogenides with topological properties and illustrates the use of circular dichroism as a guide to identify the topological character of two otherwise equivalent band dispersions, and to recognize different attributes in the band structure of similar materials.

cond-mat.mes-hall↗

arXiv2023

Unexpected Field Evaporation Sequence in $γ$-TiAl

In atom probe tomography (APT), atoms from the surface of a needle shape specimen are evaporated under a high electric field and analyzed via time of flight mass spectrometry and position sensitive detection. 3D reconstruction of the atom positions follows a simple projection law, which can sometimes lead to artifacts due to deviation from an assumed ideal evaporation sequence. Here, we revisit the evaporation behavior of [001]-oriented $γ$-TiAl using a full-dynamics simulation approach empowered by molecular dynamics. Without any knowledge of charge states or assumptions about evaporation fields, we successfully reproduced the lack of distinct Al and Ti layers observed in reconstructions of experimental data which is traditionally attributed to the retention of Al on the evaporating surface. We further showed that a step-wise bond breaking process of Ti in contrast to the simultaneous bond breaking of Al explains the seemingly counterintuitive preferential evaporation of the strongly bonded Ti atoms.

cond-mat.mtrl-sci↗

arXiv2022

Ab-Initio Simulation of Field Evaporation

A new simulation approach of field evaporation is presented. The model combines classical electrostatics with molecular dynamics (MD) simulations. Unlike previous atomic-level simulation approaches, our method does not rely on an evaporation criterion based on thermal activation theory, instead, electric-field-induced forces on atoms are explicitly calculated and added to the interatomic forces. Atoms then simply move according to the laws of classical molecular dynamics and are "evaporated" when the external force overcomes interatomic bonding. This approach thus makes no ad-hoc assumptions concerning evaporation fields and criteria, which makes the simulation fully physics-based and "ab-initio" apart from the interatomic potential. As proof of principle, we perform simulations to determine material dependent critical voltages which allow assessing the evaporation fields and the corresponding steady-state tip shapes in different metals. We also extract critical evaporation fields in elemental metals and sublimation energies in a high entropy alloy to have a more direct comparison with tabulated values. In contrast to previous approaches, we show that our method is able to successfully reproduce the enhanced zone lines observed in experimental field desorption patterns. We also demonstrate the need for careful selection of the interatomic potential by a comparative study for the example of Cu-Ni alloys.

cond-mat.mtrl-sci↗

arXiv2022

Origin of Enhanced Zone Lines in Field Desorption Maps

Artifacts in the collective desorption map of the detector hits impede a truthful reconstruction, including enhanced "zone lines" with high atomic impact intensity. Since APT is destructive, simulation is the only approach to explain the origin of these zone lines, but previous work couldn't reproduce them. Here, we use a new simulation technique that adds the full electrostatic forces to the interatomic forces in a molecular-dynamics simulation and eliminates the previous ad-hoc assumptions. We find for the canonical example of tungsten that evaporation happens when the electrostatic force overpowers the interatomic force, and the misalignment of the two forces deviates the launch direction of the atoms in certain zones, giving rise to an accumulation of hit events around zone lines.

cond-mat.mtrl-sci↗