Research Projects

Understanding the variable composition in iron oxides

Iron oxides and hydroxides of variable stoichiometry occur at the essential stages of iron ore reduction and ferrous metal corrosion (rusting). We aim at building up a fundamental understanding of how the ions (Fe²⁺, Fe³⁺, O^2-, OH^-) may arrange and rearrange to achieve such a broad composition range, in order to optimize the conditions to improve reduction processes and prevent corrosion. more

Illustrative surface phases, shown with a backdrop of surface phase diagram showing the self adsorption energy variation with electric field.

Surface Phase Diagrams for Field Evaporation

The intense electric fields such as those used in atom probe tomography (APT) can be treated as a degree of freedom for stability of different surface phases of metal. Through density functional theory (DFT) calculations on the Li (110) surface, we identify a critical field strength at which kink sites spontaneously dissolve into mobile adatom states, also enabling barrier-free diffusion across the surface. This suggests the emergence of a fluid-like, 2D adatom gas phase on lithium surfaces under high fields, even at cryogenic temperatures. This phase transition, driven by electrostatic field effects, provides a theoretical framework to explain experimental observations.
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Simulations for Field Ion Emission Microscopy Techniques

Field ion emission microscopy techniques are a group of characterization tools employing humungous electric fields. Atom probe tomography (APT), field ion microscopy (FIM), field emission microscopy (FEM), analytical field ion microscopy (AFIM) are the few of these. The strong fields applied (10⁶-10¹⁰ V/m), induce a host of interesting phenomena at/near the specimen surface. Using density functional theory (DFT) and python based analysis algorithms, we have several projects to aid and inform these characterization routines, to advance and enable new horizons for field ion emission techniques. more

Field-Controlled Evaporation Mechanisms for Surface Atoms

Extremely strong (~10 V/nm) electric fields rupturing atomic bonds is a relatively well-studied concept in the field of molecular chemistry. When extended to crystalline systems, i.e. material surfaces, this concept is known as field evaporation and its exact mechanisms become more challenging to predict. Field evaporation is the central phenomenon that enables atom probe tomography (APT), and obtaining atomically-accurate APT reconstructions will be impossible without an atomically-accurate understanding of how ions initially form and depart from the surface. By performing first-principles calculations on faceted surfaces under extreme fields, we search for such an understanding. more

Orbital Contrast in Field Ion Microscopy

method development

We simulate the ionization contrast in field ion microscopy arising from the electronic structure of the imaged surface. For this DFT calculations of the electrified surface are combined with the Tersoff-Hamann approximation to electron tunneling. The approach allows to explain the chemical contrast observed for NiRe alloys. more

Microstructure Data Mining in Atom Probe Tomography via Machine Learning

artificial intelligence and digitilization

Atom probe tomography (APT) provides three dimensional(3D) chemical mapping of materials at sub nanometer spatial resolution. In this project, we develop machine-learning tools to facilitate the microstructure analysis of APT data sets in a well-controlled way. more

Learning Dynamics of STEM Data by Enforcing Physical Consistency with Phase-Field Models

artificial intelligence and digitilization

The project’s goal is to synergize experimental phase transformations dynamics, observed via scanning transmission electron microscopy, with phase-field models that will enable us to learn the continuum description of complex material systems directly from experiment. more

Non-radiative recombination in optoelectronic devices

Optoelectronic devices allow for the direct conversion of light and electrical energy. The performance of such optoelectronic devices is limited by losses due to non-radiative recombination. We have looked at the solar cell material Cu(In,Ga)Se₂. We identified not only an effective recombination pathway at high Ga contents involving configuration changes of Ga or In anti-sites, but also extended the charge corrections to the computation of configuration coordinate diagrams. more

Current Research Projects of the Defect Chemistry and Spectroscopy group