Materials at the Atomic Scale

Understanding phase changes, including their formation and evolution, is critical for the performance of functional as well as structural materials. In this project we analyze in detail microstructural and chemical transformations of the amorphous steel Fe50Cr15Mo14C15B6 during isothermal treatments at temperatures ranging from 550 to 800 °C. [more]
Here we focus on topics that demonstrate the importance of atom probe tomography for obtaining nanostructural information that provides deep insights into the structure of metallic alloys, leading to a better understanding of their properties. [more]
Pearlitic steel wires can exhibit tensile strengths higher than 5 GPa and even up to 7 GPa after severe plastic deformation, where the deformation promotes a refinement of the lamellar structure and cementite decomposition. However, a convincing correlation between deformation and cementite decomposition in pearlite is still absent. [more]
Metallic alloys can nowadays be understood and manipulated down to near-atomic scale. This applies particularly to interfaces in high strength steels: [more]
This work led so far to several high impact publications: for the first time nanobeam diffraction (NBD) orientation mapping was used on atom probe tips, thereby enabling the high throughput characterization of grain boundary segregation as well as the crystallographic identification of phases. [more]
Commercially available materials are designed and optimised for the conventional processing route (e.g. casting, rolling and annealing) and therefore might not be optimal for LAM or might even not be suitable for LAM at all. The time-temperature profile experienced by a part produced by LAM is very different from the one produced by conventional manufacturing.  [more]
Thermoelectric (TE) materials are involved in a variety of devices converting waste heat into electrical energy, as well as for solid-state refrigeration. The energy conversion efficiency is determined by the dimensionless TE figure of merit, ZT. [more]
The CdS/CIGS interface was investigated in the literature by several techniques such as energy dispersive x-ray spectroscopy (EDX) [5-7], x-ray photoelectron spectroscopy (XPS) [8], Auger electron spectroscopy (AES) [8], secondary ion mass spectrometry (SIMS) [8], and scanning Kelvin probe microscopy (SKPM) [9]. These studies showed that the buffer/absorber layer interface is in general intermixed. [more]
Polycrystalline thin-film solar cells based on the compound semiconductors CuInSe2 (CIS) and Cu(In,Ga)Se2 (CIGS) as absorber materials are important for photovoltaic applications because of their high energy conversion efficiency, long-term stable performance, and low-cost production. [more]
Multicrystalline Silicon (mc-Si) is a common bulk material for photovoltaic due to its inexpensive growth technique. It is known that during growth and cooling, metal impurities from the sidewalls of the ingot accumulate at the grain boundaries (GBs) and locally enhance the recombination activity and therefore reduce the efficiency of the solar cell. [more]
Thin-film solar cells based on the kesterite structured compound semiconductor Cu2ZnSn(S,Se)4 (CZTSSe) comprise inexpensive, earth-abundant, and non-toxic elements while maintaining favorable, optical, electrical properties (such as high absorption coefficient). [more]
We introduce a new experimental approach to the compositional and thermomechanical design and rapid maturation of bulk structural materials. This method, termed Rapid Alloy Prototyping (RAP), is based on semi-continuous high-throughput bulk casting, rolling, heat treatment and sample preparation techniques. 45 material conditions – i.e. 5 alloys with systematically varied composition, each modified by 9 different aging treatments – were produced and investigated within 35 hours. This accelerated screening of the tensile, hardness and microstructural properties as a function of chemical and thermomechanical parameters allows for the highly efficient and knowledge-based design of bulk structural alloys. [more]
Understanding alloying and thermal processing at an atomic scale is essential for the optimal design of high carbon (0.71 wt.%) bainitic-austenitic transformation induced plasticity (TRIP) steels. We investigate the influence of the austempering temperature, chemical composition (especially of the Si-to-Al ratio) and partitioning on the nanostructure and mechanical behavior of these steels by atom probe tomography (APT). The effects of the austempering temperature and of Si and Al on the compositional gradients across the phase boundaries between retained austenite and bainitic ferrite are studied. [more]
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