arXiv subjects

Joke Hadermann

Publications and source records attributed to Joke Hadermann.

9 recordsLinked to original sources

arXiv2026

A 4D-STEM Tomographic Framework Assisted by Object Tracking for Nanoparticle Structure Determination

Three-dimensional electron diffraction (3D ED) has emerged as a powerful method for solving the structures of sub-micron-sized particles down to nanoparticles. However, it faces technical challenges when applied to beam-sensitive samples or agglomerated nanoparticles. This study presents a novel approach that combines 4D-STEM tomography with object tracking and segmentation algorithms to overcome these limitations and achieve single-crystalline 3D ED datasets from nanopowder samples. The method and data quality are assessed on brookite TiO2 nanorods and beam-sensitive CsPbBr3 nanoparticles. To finely sample the reciprocal-space, the data acquisition was automated to acquire hundreds of 4D-STEM scans at fine tilt steps using a slightly convergent beam (0.6 to 1 mrad). Compared to conventional 3D ED methodologies, the proposed method provides enhanced signal-to-noise ratio, low illumination time for reducing beam damage, and the ability to analyze multiple particles from a single tomographic dataset. The procedure is optimized to be feasible using commercially available desktops and detectors. This extends the method applicability to systems and samples that were very challenging for conventional 3D ED methods, by eliminating several technical challenges for the data acquisition.

physics.ins-det↗

arXiv2025

Removing constraints of 4D-STEM with a framework for event-driven acquisition and processing

Pixelated detectors in scanning transmission electron microscopy (STEM) generate large volumes of data, often tens to hundreds of GB per scan. However, to make current advancements scalable and enable widespread adoption, it is essential to use the most efficient representation of an electron's information. Event-driven direct electron detectors, such as those based on the Timepix3 chip, offer significant potential for electron microscopy, particularly for low-dose experiments and real-time data processing. In this study, we compare sparse and dense data representations in terms of their size and computational requirements across various 4D-STEM scenarios, including high-resolution imaging and nano-beam electron diffraction. The advantages of performing 4D-STEM in an event-driven mode - such as reduced requirements in memory, bandwidth, and computational demands - can only be fully leveraged if the entire acquisition and processing pipeline is optimized to work directly with the event format, avoiding intermediate dense representations. We introduce a framework designed for acquisition and processing based on this event format, and demonstrate live processing of event-driven 4D-STEM, including analytical ptychography.

physics.ins-det↗

arXiv2024

Toward Mass-Production of Transition Metal Dichalcogenide Solar Cells: Scalable Growth of Photovoltaic-Grade Multilayer WSe2 by Tungsten Selenization

Semiconducting transition metal dichalcogenides (TMDs) are promising for high-specific-power photovoltaics due to desirable band gaps, high absorption coefficients, and ideally dangling-bond-free surfaces. Despite their potential, the majority of TMD solar cells are fabricated in a non-scalable fashion using exfoliated materials due to the absence of high-quality, large-area, multilayer TMDs. Here, we present the scalable, thickness-tunable synthesis of multilayer tungsten diselenide (WSe$_{2}$) films by selenizing pre-patterned tungsten with either solid source selenium or H$_{2}$Se precursors, which leads to smooth, wafer-scale WSe$_{2}$ films with a layered van der Waals structure. The films have charge carrier lifetimes up to 144 ns, over 14x higher than large-area TMD films previously demonstrated. Such high carrier lifetimes correspond to power conversion efficiency of ~22% and specific power of ~64 W g$^{-1}$ in a packaged solar cell, or ~3 W g$^{-1}$ in a fully-packaged solar module. This paves the way for the mass-production of high-efficiency multilayer WSe$_{2}$ solar cells at low cost.

cond-mat.mtrl-sci↗

arXiv2023

Acquisition of high-quality three-dimensional electron diffuse scattering data

The diffraction patterns of crystalline materials with local order contain sharp Bragg reflections as well as highly structured diffuse scattering. The instrumental requirements, experimental parameters and data processing techniques for obtaining high-quality diffuse scattering data have previously been determined for X-ray and neutron diffraction, but not yet for electron diffraction. In this study, we show that the spatial resolution of the diffuse scattering in three-dimensional electron diffraction (3D ED) data depends on various effects, including the convergence of the electron beam, the point spread function of the detector and the crystal mosaicity. In contrast to single-crystal X-ray diffraction, the detector point spread function for 3D ED is broader for a hybrid pixel detector than for a CCD. In our study, we also compare the diffuse scattering in 3D ED data with the diffuse scattering in single-crystal X-ray diffraction data and show that the diffuse scattering in 3D ED data can be obtained with a quality comparable to that from single-crystal X-ray diffraction. As electron diffraction requires much smaller crystal sizes than X-ray diffraction, this opens up the possibility to investigate the local structure of many technologically relevant materials for which no crystals large enough for single-crystal X-ray diffraction are available.

cond-mat.mtrl-sci↗

arXiv2020

$\require{mhchem}$Misfit phase $\ce{(BiSe)_{$1.10$}NbSe2}$ as the origin of superconductivity in nobium-doped bismuth selenide

$\require{mhchem}$Topological superconductivity is of great contemporary interest and has been proposed in doped $\ce{Bi2Se3}$ in which electron-donating atoms such as Cu, Sr or Nb have been intercalated into the $\ce{Bi2Se3}$ structure. For $\ce{Nb_{x}Bi2Se3}$, with $\text{T}_\text{c} \sim 3 \ \text{K}$, it is assumed in the literature that Nb is inserted in the van der Waals gap. However, in this work an alternative origin for the superconductivity in Nb-doped $\ce{Bi2Se3}$ is established. In contrast to previous reports, it is deduced that Nb intercalation in $\ce{Bi2Se3}$ does not take place. Instead, the superconducting behaviour in samples of nominal composition $\ce{Nb_{x}Bi2Se3}$ results from the $\ce{(BiSe)_{$1.10$}NbSe2}$ misfit phase that is present in the sample as an impurity phase for small $x$ ($0.01 \leq x \leq 0.10$) and as a main phase for large $x$ ($x = 0.50$). The structure of this misfit phase is studied in detail using a combination of X-ray diffraction and transmission electron microscopy techniques.

cond-mat.supr-con↗

arXiv2020

Compatibility of $Zr_{2}AlC$ MAX phase-based ceramics with oxygen-poor, static liquid lead-bismuth eutectic

This work investigates the compatibility of $Zr_{2}AlC$ MAX phase-based ceramics with liquid LBE, and proposes a mechanism to explain the observed local $Zr_{2}AlC$/LBE interaction. The ceramics were exposed to oxygen-poor ($C_{O}\le2.2 \cdot10^{-10}$ mass%), static liquid LBE at 500{\deg}C for 1000 h. A new $Zr_{2}(Al,Bi,Pb)C$ MAX phase solid solution formed in-situ in the LBE-affected $Zr_{2}AlC$ grains. Out-of-plane ordering was favorable in the new solid solution, whereby $\textit{A}$-layers with high and low-Bi/Pb contents alternated in the crystal structure, in agreement with first-principles calculations. Bulk $Zr_{2}(Al,Bi,Pb)C$ was synthesized by reactive hot pressing to study the crystal structure of the solid solution by neutron diffraction.

cond-mat.mtrl-sci↗

arXiv2012

Frustrated pentagonal Cairo lattice in the non-collinear antiferromagnet Bi4Fe5O13F

The crystal and magnetic structures and underlying magnetic interactions of Bi4Fe5O13F, a model system for studying the physics of the Cairo pentagonal spin lattice, are investigated by transmission electron microscopy, low-temperature synchrotron x-ray and neutron powder diffraction, thermodynamic measurements, and density functional band-structure calculations. The crystal structure of Bi4Fe5O13F contains infinite rutile-like chains of edge-sharing FeO6 octahedra interconnected by the Fe2O7 groups of two corner-sharing FeO4 tetrahedra. The cavities between the chains are filled with the fluorine-centered Bi4F tetrahedra. The Fe3+ cations form pentagonal units that give rise to an unusual topology of frustrated exchange couplings and underlie a sequence of the magnetic transitions at T1= 62 K, T2 = 71 K, and TN = 178 K. Below T1, Bi4Fe5O13F forms a fully ordered non-collinear antiferromagnetic structure, whereas the magnetic state between T1 and TN may be partially disordered according to the sizable increase in the magnetic entropy at T1 and T2. Therefore, Bi4Fe5O13F shows the evidence of intricate magnetic transitions that were never anticipated for the pentagonal Cairo spin lattice. Additionally, it manifests a sillimanite (Al2SiO5)-based homologous series of compounds that feature the pentagonal magnetic lattice spaced by a variable number of octahedral units along the rutile-type chains.

cond-mat.mtrl-sci↗

arXiv2010

Bulk magnetic order in a two dimensional Ni1+/Ni2+ (d9/d8) nickelate, isoelectronic with superconducting cuprates

Bulk magnetic order in two dimensional La4Ni3O8 nickelate with Ni1+/Ni2+ (d9/d8), isoelectronic with superconducting cuprates is demonstrated experimentally and theoretically. Magnetization, specific heat and 139La NMR evidence a transition at 105 K to an antiferromagnetic state. Theoretical calculations by DFT relate the transition to a nesting instability of the Fermi surface with ordering wave-vector Q = [1/3, 1/3, 0].

cond-mat.str-el↗

arXiv2007

Spin ladder compound Pb(0.55)Cd(0.45)V(2)O(5): synthesis and investigation

The complex oxide Pb(0.55)Cd(0.45)V(2)O(5) was synthesized and investigated by means of X-ray powder diffraction, electron diffraction, magnetic susceptibility measurements and band structure calculations. Its structure is similar to that of MV(2)O(5) compounds (M = Na, Ca) giving rise to a spin system of coupled S=1/2 two-leg ladders. Magnetic susceptibility measurements reveal a spin gap-like behavior with Δ~ 270 K and a spin singlet ground state. Band structure calculations suggest Pb(0.55)Cd(0.45)V(2)O(5) to be a system of weakly coupled dimers in perfect agreement with the experimental data. Pb(0.55)Cd(0.45)V(2)O(5) provides an example of the modification of the spin system in layered vanadium oxides by cation substitution. Simple correlations between the cation size, geometrical parameters and exchange integrals for the MV(2)O(5)-type oxides are established and discussed.

cond-mat.str-el↗