arXiv subjects

Tobias Meyer

Publications and source records attributed to Tobias Meyer.

14 recordsLinked to original sources

arXiv2026

Tracing boron diffusion into a textured silicon solar cell using electron beam induced current in a scanning transmission electron microscope

The light absorption of [001] grown single-crystalline silicon wafers can be enhanced by chemical etching, e.g., with potassium hydroxide, resulting in a pyramid-like surface texture. Alongside advantageous photon harvesting in solar cells, the surface roughness leads to drawbacks when measuring diffusion behaviour of dopants in the heterogeneous structure. In this paper, we employ experimental and simulated scanning transmission electron beam induced current in combination with simulation of boron diffusion in a self-consistent framework to trace the dopant distribution underneath the pyramid-like surface texture. In order to account for surface recombination, an effective model projecting the system along the electron beam propagation direction is used in the EBIC simulation enabling a comparison to entire two-dimensional experimental maps. We find a good agreement between simulated and experimental data and thoroughly discuss how EBIC can be used in future experiments to quantify weak electric fields.

physics.app-ph↗

arXiv2026

A Local Probe Mass Spectrometer for Localized and Sensitive Product Detection in Environmental Electron Microscopy

Aberration-corrected environmental transmission electron microscopy (ETEM) enables atomic-resolution imaging of dynamic catalytic processes. Correlating atomic-scale structural changes with reaction products detected by mass spectrometry offers a powerful route to uncover catalytic mechanisms. However, current approaches face fundamental limitations: closed-cell ETEM setups suffer from diffuse scattering by SiN windows, degrading spatial resolution and sensitivity, while open-cell configurations enable high-resolution imaging and maintain high sensitivity but suffer from significant dilution of reaction products during transport to the mass spectrometer (MS). To overcome these challenges, we develop a Local Probe Mass Spectrometer (LPMS) integrated with aberration-corrected ETEM. The setup combines a DENSsolution Stream holder with a MS. To preserve spatial resolution, both top and bottom SiN membranes of the MEMS chip are removed, while the gas environment is maintained via the ETEM chamber. Reaction products are sampled locally via a micro-capillary positioned near the catalyst and connected to a holder gas line that delivers the gas to the MS. Initial validation in environmental SEM confirmed controlled gas delivery to the MS. Co3O4 nanoplates serve as a model catalyst due to their inherent electron transparency, enabling atomic-resolution imaging without FIB lamella preparation and associated ion-beam damage. A novel micro-shuttle transfer strategy enables controlled placement of a defined number of nanoplates at the reaction site with precise crystallographic orientation. This establishes the foundation for quantitative structure reactivity correlation by enabling simultaneous, spatially resolved detection of reaction products and atomic-scale structural dynamics.

cond-mat.mtrl-sci↗

arXiv2026

Quantitative models for excess carrier diffusion and recombination in STEM-EBIC experiments on semiconductor nanostructures

The increased complexity and reduced size of (opto-)electronic devices demands for quantitative descriptions of excess carrier transport and recombination via various mechanisms. In addition, experimental methods capable of resolving carrier dynamics on the nanometer scale are required. In this paper, we present a quantitative model of a confined geometry including recombination at two surfaces, which is very generic for electron beam induced current measurements in a scanning transmission electron microscope - a method which offers atomic scale spatial resolution. The model is based on analytical considerations as well as finite element simulations and underlying assumptions are subjected to an in-depth discussion. Finally, the successfull application to experimental data obtained on the complex oxide SrTi0.995Nb0.005O3 demonstrates the practicality and robustness of the approach, which enables the precise determination of its bulk diffusion length of L = 10.2 +- 0.1 nm.

cond-mat.mes-hall↗

arXiv2025

Molecular Beam Epitaxy of 2H-TaS$_2$ few-layers on GaN(0001)

2H-TaS$_2$ few layers have been grown epitaxially onto GaN(0001). A high substrate growth temperature of 825$^{\circ}$C induces best structural properties of the overlayer, as revealed by in-situ electron diffraction (RHEED and LEED). The 2D-overlayer grows unstrained right after deposition of a monolayer. However, evidence of pits at the interface is provided by scanning transmission electron microscopy, most probably due to GaN thermal decomposition at the high growth temperature. In-situ x-ray photoemission spectroscopy shows core level shifts that are consistently related to electron transfer from the n-GaN(0001) to the 2H-TaS$_2$ epitaxial layer as well as the formation of a high concentration of nitrogen vacancies close to the interface. Further, no chemical reaction at the interface between the substrate and the grown TaS$_2$ overlayer is deduced from XPS, which corroborates the possibility of integration of 2D 2H-TaS$_2$ with an important 3D semiconducting material like GaN.

cond-mat.mtrl-sci↗

arXiv2025

Sequential tilting 4D-STEM for improved momentum-resolved STEM field mapping

Momentum-resolved scanning transmission electron microscopy (MRSTEM) is a powerful phase-contrast technique that can map lateral magnetic and electric fields ranging from the micrometer to the subatomic scale. Resolving fields ranging from a few nanometers to a few hundred nanometers, as well as across material junctions, is particularly important since these fields often determine the functional properties of devices. However, it is also challenging since they are orders of magnitude smaller than atomic electric fields. Thus, subtle changes in diffraction conditions lead to significant changes in the measured MRSTEM signal. One established approach to partially overcome this problem is precession electron diffraction, in which the incident electron beam is continuously precessed while precession-averaged diffraction patterns are acquired. Here, we present an alternative approach in which we sequentially tilt the incident electron beam and record a full diffraction pattern for each tilt and spatial position. This approach requires no hardware modification of the instrument and enables the use of arbitrary beam tilt patterns that can be optimized for specific applications. Furthermore, recording diffraction patterns for every beam tilt allows access to additional information. In this work, we use this information to create virtual large-angle convergent beam electron diffraction (vLACBED) patterns to assess MRSTEM data quality and improve field measurements by applying different data analysis methods beyond simple averaging. The presented data acquisition concept can readily be applied to other 4D-STEM applications.

cond-mat.mtrl-sci↗

arXiv2025

Distribution of ${}^{7}$Li Implants in Nb Films for a Sterile Neutrino Search

The BeEST experiment is measuring the ${}^{7}$Li recoil spectrum from the decay of ${}^{7}$Be implanted into Ta-based sensors to provide the most stringent limits on the existence of sterile neutrinos in the sub-MeV mass range. Its sensitivity is limited by spectral broadening due to interactions between the atomic shell of the ${}^{7}$Be/${}^{7}$Li and the Ta sensor film. This study is investigating the suitability of Nb as an alternative sensor material by scanning transmission electron microscopy (STEM) and atom probe tomography (APT) of ${}^{7}$Li-implanted Nb films. STEM does not detect any change in the microstructure of polycrystalline Nb due to ${}^{7}$Li implantation. APT reveals some segregation of ${}^{7}$Li at grain boundaries in Nb. While this may slightly alter the ${}^{7}$Li binding energies, the effect on the recoil spectrum is not expected to be strong enough to preclude using Nb-based detectors in future phases of the BeEST experiment.

physics.ins-det↗

arXiv2025

Atomic-Scale Investigation of an Asymmetric SrTiO$_{3}$ Grain Boundary

Grain boundaries (GBs) in oxide perovskites significantly influence their functional properties. This study examines the atomic-scale structure and composition of a faceted asymmetric grain boundary in strontium titanate (SrTiO$_3$) using scanning transmission electron microscopy (STEM), atom probe tomography (APT), and density functional theory (DFT). STEM and APT reveal an atomically sharp boundary with asymmetric and symmetric facets, marked by strong Sr depletion over a width of less than 1 nm. STEM-EELS shows Ti concentration variations of up to 20% between facets, while APT constrains this variation to less than 10%. DFT$+U$ calculations of a symmetric $Σ$5 facet confirm that Sr depletion minimizes boundary energy while maintaining Ti content. The variation in Ti suggests cation mobility that enables local energy minimization. Differences in facet surface energies likely drive Ti redistribution, offering strategies for GB structure control. This combined experimental-theoretical approach provides key insights into the structure and energy landscape of GBs in SrTiO$_3$, aiding in the prediction of their impact on ionic and electronic transport.

cond-mat.mtrl-sci↗

arXiv2024

Growth Engineering of SrNbO3 Perovskite Oxide by Pulsed Laser Deposition and Molecular Beam Epitaxy

Molecular beam epitaxy (MBE) is a state-of-the-art technique for depositing thin films with precise stoichiometric control. However, when depositing oxides of perovskite-type ABO3, this process becomes challenging as controlling the flux rate of A and B simultaneously in the presence of oxygen is difficult. In this work, by utilizing e-beam-assisted oxide MBE, we successfully deposited SrNbO3 epitaxial thin films. A buffer layer of SrTiO3 perovskite oxide, prepared by pulsed laser deposition (PLD), was used to improve the growth of this oxide significantly. This method overcomes the ultimatum of stabilizing perovskite oxide growth using MBE since the valence mismatch between the substrate and the films were effectively masked by the ultra-thin SrTiO3 and further supported interfacial charge transfer. Interestingly, we also discovered that the perovskite oxides SrNbO3 and SrTiO3 replace K in KTaO3 substrates by Sr, regardless of the deposition technique used, which is generally considered a reason for many interfacial effects. The growth of SrNbO3 was unaffected by the K deficiency when the stable buffer layer was introduced.

cond-mat.mtrl-sci↗

arXiv2022

Microstructural analysis of GaN films grown on (1 0 0) MgF$_2$ substrate by 4D nanobeam diffraction and energy-dispersive X-ray spectrometry

The use of highly efficient and solarblind GaN photocathodes as part of multichannel plate UV detectors for applications in astronomy would strongly benefit from the direct growth of GaN on typical window materials with high transmission down to the deep UV range. GaN growth on MgF$_2$ substrates by plasma-assisted molecular beam epitaxy has recently been demonstrated. Here, we report an extensive scanning transmission electron microscopy study of the thin film microstructure for growth at 525 $^{\circ}$C and 650 $^{\circ}$C on (100) MgF$_2$. These results are systematically supported by X-ray diffraction reciprocal space maps. For both growth temperatures predominant cubic (111), (115) and (110) GaN is found with no preferred nucleation on the substrate and typical grain sizes of 100-200 nm. All observed orientations can be understood as the result of first and second order twins on different $\{111\}$ planes related to the underlying substrate. The higher growth temperature shows a strongly increased twin density along with a higher surface roughness. Furthermore, grains with cubic (110) GaN growth show a reduced density and a reduced size of about 20 nm. Furthermore, in-diffusion of Mg and F into the GaN is observed, which is accompanied by the formation of cavities in the MgF$_2$ directly at the interface.

physics.app-ph↗

arXiv2021

Spatially Resolving the Enhancement Effect in Surface-Enhanced Coherent Anti-Stokes Raman Scattering by Plasmonic Doppler Gratings

In this work, we introduce the platform of plasmonic Doppler grating (PDG) to experimentally investigate the enhancement effect of plasmonic gratings in the input and output beams of nonlinear surface-enhanced coherent anti-Stokes Raman scattering (SECARS). PDGs are designable azimuthally chirped gratings that provide broadband and spatially dispersed plasmonic enhancement. Therefore, they offer the opportunity to observe and compare the overall enhancement from different combinations of enhancement in individual input and output beams. We first confirm PDG's capability of spatially separating the input and output enhancement in linear surface-enhanced fluorescence and Raman scattering. We then investigate spatially resolved enhancement in nonlinear SECARS, where coherent interaction of the pump, Stokes, and anti-Stokes beams is enhanced by the plasmonic gratings. By mapping the SECARS signal and analyzing the azimuthal angle-dependent intensity, we characterize the enhancement at individual frequencies. Together with theoretical analysis, we show that while simultaneous enhancement in the input and output beams is important for SECARS, the enhancement in the pump and anti-Stokes beams plays a more critical role in the overall enhancement than that in the Stokes beam. This work provides an insight into the enhancement mechanism of plasmon-enhanced spectroscopy, which is important for the design and optimization of plasmonic gratings. The PDG platform may also be applied to study enhancement mechanisms in other nonlinear light-matter interactions or the impact of plasmonic gratings on the fluorescence lifetime.

physics.optics↗

arXiv2020

Site-specific plan-view TEM lamella preparation of pristine surfaces with a large field of view

Transmission electron microscopy has become a major characterisation tool with an ever increasing variety of methods being applied in wide range of scientific fields. However, the probably most famous pitfall in related workflows is the preparation of high-quality electron-transparent lamellae enabling for extraction of valuable and reliable information. Particularly in the field of solid state physics and materials science, it is often required to study the surface of a macroscopic specimen with plan-view orientation. Nevertheless, despite tremendous advances in instrumentation, i.e. focused ion beam, the yield of existing plan-view lamellae preparation techniques is relatively low compared to cross-sectional extraction methods. Furthermore, techniques relying on mechanical treatments, i.e. conventional preparation, compromise site-specifity. In this paper, we demonstrate that by combining a mechanical grinding step prior to backside lift-out in the focused ion beam plan-view lamellae preparation becomes increasingly easy. The suggested strategy combines site-specifity with micrometer precision as well as possible investigation of pristine surfaces with a field of view of several hundred square micrometers.

physics.app-ph↗

arXiv2020

Phase transitions in a perovskite thin film studied by environmental in-situ heating nano-beam electron diffraction

The rich phase diagram of bulk Pr$_{1-x}$Ca$_{x}$MnO$_3$ resulting in a high tunability of physical properties gave rise to various studies related to fundamental research as well as prospective applications of the material. Importantly, as a consequence of strong correlation effects, electronic and lattice degrees of freedom are vigorously coupled. Hence, it is debatable whether such bulk phase diagrams can be transferred to inherently strained epitaxial thin films. In this paper, the structural orthorhombic to pseudo-cubic transition for $x=0.1$ is studied in ion-beam sputtered thin films and point out differences to the respective bulk system by employing in-situ heating nano-beam electron diffraction to follow the temperature dependence of lattice constants. In addition, it is demonstrated that controlling the environment during heating, i.e. preventing oxygen loss, is crucial in order to avoid irreversible structural changes, which is expected to be a general problem of compounds containing volatile elements under non-equilibrium conditions.

cond-mat.mtrl-sci↗

arXiv2020

Virtual H&E Histology by Fiber-Based Picosecond Two-Photon Microscopy

Two-Photon Microscopy (TPM) can provide three-dimensional morphological and functional contrast in vivo. Through proper staining, TPM can be utilized to create virtual, H&E equivalent images and thus can improve throughput in histology-based applications. We previously reported on a new light source for TPM that employs a compact and robust fiber-amplified, directly modulated laser. This laser is pulse-to-pulse wavelength switchable between 1064 nm, 1122 nm, and 1186 nm with an adjustable pulse duration from 50ps to 5ns and arbitrary repetition rates up to 1MHz at kW-peak powers. Despite the longer pulse duration, it can achieve similar average signal levels compared to fs-setups by lowering the repetition rate to achieve similar cw and peak power levels. The longer pulses lead to a larger number of photons per pulse, which yields single shot fluorescence lifetime measurements (FLIM) by applying a fast 4 GSamples/s digitizer. In the previous setup, the wavelengths were limited to 1064 nm and longer. Here, we use four wave mixing in a non-linear photonic crystal fiber to expand the wavelength range down to 940 nm. This wavelength is highly suitable for imaging green fluorescent proteins in neurosciences and stains such as acridine orange (AO), eosin yellow (EY) and sulforhodamine 101 (SR101) used for histology applications. In a more compact setup, we also show virtual H&E histological imaging using a direct 1030 nm fiber MOPA.

physics.med-ph↗

arXiv2019

Plasma Profiling Time-of-Flight Mass Spectrometry for Fast Elemental Analysis of Semiconductor Structures with Depth Resolution in the Nanometer Range

Plasma profiling time of flight mass spectrometry (PP-TOFMS) has recently gained interest, as it enables the elemental profiling of semiconductor structures with high depth resolution in short acquisition times. As recently shown by Tempez et al., PP-TOFMS can be used to obtain the composition in the structures for modern field effect transistors [1]. There, the results were compared to conventional SIMS measurements. In the present study, we compare PP-TOFMS measurements of an Al-/In-/GaN quantum well multi stack to established micro- and nano-analysis techniques like cathodoluminescence (CL), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). We show that PP-TOFMS is able to resolve the layer structure of the sample even more than 500 nm deep into the sample and allows the determination of a relative elemental composition with an accuracy of about 10 rel. %. Therefore, it is an extremely rapid alternative method to obtain semiconductor elemental depth profiles without expensive and time consuming sample preparation as it is needed for TEM. Besides, PP-TOFMS offers better depth resolution and more elemental information than for example electrochemical capacitance-voltage (ECV), as the acquisition of all elements occurs in parallel and not only electrically (ECV) or optically (CL) active elements are observed.

physics.app-ph↗