arXiv subjects

Colin Gilgenbach

Publications and source records attributed to Colin Gilgenbach.

11 recordsLinked to original sources

arXiv2026

On Transmission Function Amplitude and Phase Recovery in Multislice Electron Ptychography

{Multislice electron ptychography commonly accounts for inelastic scattering by including an absorptive object potential in the reconstruction forward model that attenuates the elastic signal. However, it remains unclear how the reconstruction is quantitatively impacted by thermal scattering. Here, we use the quantum excitation of phonons (QEP) formalism, which explicitly separates elastic and inelastic (thermal diffuse) scattering within a single multislice propagation, to simulate four-dimensional scanning transmission electron microscopy (4D STEM) datasets of PbTiO$_3$ and SrTiO$_3$ and reconstruct their phase and amplitude. We find that reconstructions of the QEP total and elastic-only datasets are nearly indistinguishable across sample thicknesses from 11 to 40 nm and across atomic species, demonstrating that the reconstruction is largely insensitive to incoherent thermal diffuse scattering within the collected angular range. Reconstructions from multislice phase-only simulations further confirm that appreciable amplitude does not arise from multiple elastic scattering, but instead reflects attenuation of the coherent elastic signal due to thermal scattering. Further comparison of the QEP elastic-only reconstruction with absorptive multislice simulations reveals substantial amplitude contrast deviations for heavy Pb columns (up to 17\%), arising from the approximations used to evaluate the absorptive potential for the 4D STEM simulation. These results thus indicate that reconstruction phase and amplitude accuracy are not significantly limited by the absorptive potential forward model, even in the presence of thermal diffuse scattering.

cond-mat.mtrl-sci↗

arXiv2025

Direct determination of antiferroelectric-to-ferroelectric phase transition pathways in PbZrO$_3$ with Operando Electron Microscopy

Under a sufficiently high applied electric field, a non-polar antiferroelectric material, such as \ce{PbZrO3}, can undergo a rapid transformation to a polar ferroelectric phase. While this behavior is promising for energy storage and electromechanical applications, a complete understanding of the atomic-scale mechanisms governing the phase transition remain elusive. Here, we employ \textit{operando} scanning transmission electron microscopy electric field biasing to directly resolve the antiferroelectric-to-ferroelectric transition pathway in \ce{PbZrO3} thin films under device-relevant conditions. Atomic-resolution imaging reveals a multi-step transition that includes several metastable phases. Complementary nano-beam electron diffraction and atomic scale analysis further show that this pathway and its end states can be modulated, leading to the formation of a \quotes{dead layer} near the substrate with suppressed switching behavior. Taking advantage of this depth-dependent heterogeneity, dynamic phase transformations are observed between coexisting antiferroelectric and metastable ferroelectric phases. At this dynamic transition front, repeated phase interconversion is shown to be driven by competing internal (due to substrate clamping and extended defects) and external fields, allowing the relative energies of intermediate phases to be compared as a function of electric field. This work highlights the critical role of local energetics in phase stability and provides key experimental insights into field-induced phase transitions, guiding the design of antiferroelectric-based devices.

cond-mat.mtrl-sci↗

arXiv2025

Operando Electron Microscopy of Nanoscale Electronic Devices on Non-Conductive Substrates

Achieving operating conditions comparable to ``bulk'' electronic devices, such as thin film capacitors, during \textit{operando} electron microscopy remains challenging, particularly when devices are grown on non-conductive substrates. Limited precision of focused ion beam milling for sample preparation often necessitates the use of conductive substrates or artificially thick layers that differ from actual device architectures. These modifications can alter native strain, electrostatic boundary conditions, and ultimately device response. Here, we present a generic and versatile workflow for \textit{operando} biasing of thin-film capacitors in the (scanning) transmission electron microscope, including sample fabrication and device operation. By introducing a patterned insulating barrier adjacent to the bulk-characterized capacitors, our approach enables sample preparation without altering the original film structure. As a case study, we apply the method to a piezoelectric thin-film capacitor grown on an insulating substrate, and demonstrate that it preserves the boundary-condition-sensitive domain switching at the atomic scale under applied electric fields. Overall, the process can help to establish a foundation for systematic \textit{operando} studies of complex thin-film systems under representative bulk testing geometries.

cond-mat.mtrl-sci↗

arXiv2025

Optimizing Atomic Number Contrast in Multislice Electron Ptychography

Here we explore the atomic number ($Z$) dependence of multislice electron ptychography and approaches to optimize Z sensitivity. Specifically, we show that ptychography's $Z$-dependence is highly dependent on the integrated area of an atom column considered. A monotonic $Z$-dependence is found when the reconstructed projected atomic potentials are integrated over a small region. When increasing the integration area, $Z$-contrast changes significantly, becoming highly non-monotonic and following trends in the orbital shell-structure. Moreover, the reconstructed projected potential aligns with the transmission function with an overall deviation of only 2.4\%. The non-monotonic $Z$-dependence is further shown to be useful to accentuate contrast between certain elements, allowing for distinguishability of elements that are only a single atomic number apart, and even in $>$ 20 nm thick samples. This is demonstrated for $\beta$-CuZn ($Z$ = 29 and 30), with the differentiability between the elements explored for different signal quantification methods. The impact of electron dose and finite effective source size are also considered. These results demonstrate that the atom column integration area can optimize ptychographic $Z$-contrast for specific applications and experimental conditions.

cond-mat.mtrl-sci↗

arXiv2025

phaser: A unified and extensible framework for fast electron ptychography

We present \code{phaser}, an open-source Python package that provides a unified interface to both conventional and gradient descent-based ptychographic algorithms. Features such as mixed-state probe, probe position correction, and multislice ptychography make experimental reconstructions practical and robust. Reconstructions are specified in a declarative format and can be run from a command line, Jupyter notebook, or web interface. Multiple computational backends are supported to provide maximum flexibility. With the JAX computational backend, a six-fold improvement in iteration speed is achieved over a widely used package implemented in MATLAB, fold\_slice/PtychoShelves. We report reconstruction success for a variety of experimental datasets, and detail the effects of regularization on convergence and reconstruction quality. The software promises to speed the application and development of ptychographic methods for materials science.

physics.comp-ph↗

arXiv2025

Grain Boundary Space Charge Engineering of Solid Oxide Electrolytes: Model Thin Film Study

Grain boundaries (GB) profoundly influence the electrical properties of polycrystalline ionic solids. Yet, precise control of their transport characteristics has remained elusive, thereby limiting the performance of solid-state electrochemical devices. Here, we demonstrate unprecedented manipulation of space charge controlled ionic grain boundary resistance (up to 12 orders of magnitude) in metal oxide thin films. We exploit the orders of magnitude higher grain boundary diffusivities of substrate cation elements (i.e. Al from $Al_2O_3$ and Mg from MgO) relative to the bulk to modify the grain boundary chemistry, and thereby GB core charge, in a model oxygen ion conducting polycrystalline thin film solid electrolyte, Gd-doped $CeO_2$. This approach, confirmed jointly by TEM imaging and by extracting the respective GB and bulk diffusivities from measured SIMS profiles, enabled us to selectively control the chemistry of the GBs, while minimally modifying grain (bulk) chemistry or film microstructure, thereby ruling out potential effects of microstructure, strain or secondary phases. Broad tuning of GB space charge potentials is achieved by manipulating GB core charge density by over an order of magnitude, thereby providing a powerful tool for systematic studies of grain boundary phenomena across various functional materials. The implications of such control are far-reaching in achieving new functionality, improving efficiency and longevity of solid-state electrochemical devices.

cond-mat.mtrl-sci↗

arXiv2024

Quantifying Implantation Induced Damage and Point Defects with Multislice Electron Ptychography

Here, we use multislice electron ptychography to quantify damage introduced by ion implantation of Er into 4H-SiC. Comparing reconstructed volumes from experiment (each 2,000 nm$^{3}$) along the implantation direction, the crystal damage is quantified and compared to pristine SiC. Using simulations, we establish that the implantation-induced static displacements limit both Er dopant and silicon vacancy detection. The corresponding damage in the experiment is found to occur up a depth of 100 nm and significantly deeper than expected from implantation simulations, ignoring crystallography. Beyond this depth, we show that silicon vacancies can be identified within the sampled volume and used to measure their local strain. Overall, these results underscore the power of multislice electron ptychography to quantify the impacts of implantation and as a tool to help guide electronic device process optimization.

cond-mat.mtrl-sci↗

arXiv2024

Sensitivity of Multislice Electron Ptychography to Point Defects: A Case Study in SiC

Here, we evaluate multislice electron ptychography as a tool to carry out depth-resolved atomic resolution characterization of point defects, using silicon carbide as a case study. Through multislice electron scattering simulations and multislice ptychographic reconstructions, we investigate the phase contrast arising from individual silicon vacancies, antisite defects, and a wide range of substitutional transition metal dopants (V\textsubscript{Si} to W\textsubscript{Si}) and potential detectability. Simulating defect types, positions, and microscope conditions, we show that isolated point defects can be located within a unit cell along the sample's depth. The influence of electron energy, dose, defocus, and convergence semi-angle is also explored to determine their role in governing defect contrast. These results guide experiments aiming to analyze point defects with multislice electron ptychography.

cond-mat.mtrl-sci↗

arXiv2024

Bridging experiment and theory of relaxor ferroelectrics at the atomic scale with multislice electron ptychography

Introducing structural and/or chemical heterogeneity into otherwise ordered crystals can dramatically alter material properties. Lead-based relaxor ferroelectrics are a prototypical example, with decades of investigation having connected chemical and structural heterogeneity to their unique properties. While theory has pointed to the formation of an ensemble of ``slush''-like polar domains, the lack of direct, spatially resolved volumetric data comparable to simulations presents a significant challenge in measuring the spatial distribution and correlation of local chemistry and structure with the physics underlying relaxor behavior. Here, we address this challenge through three-dimensional volumetric characterization of the prototypical relaxor ferroelectric \ce{0.68Pb(Mg$_{1/3}$Nb$_{2/3}$)O3-0.32PbTiO$_3$} using multislice electron ptychography. Direct comparison with molecular dynamics simulations reveals the intimate relationship between the polar structure and unit-cell level charge imbalance induced by chemical disorder. Further, polar nanodomains are maintained through local correlations arising from residual short-range chemical order. Acting in concert with the chemical heterogeneities, it is also shown that compressive strain enhances out-of-plane correlations and ferroelectric-like order without affecting the in-plane relaxor-like structure. Broadly, these findings provide a pathway to enable detailed atomic scale understanding for hierarchical control of polar domains in relaxor ferroelectric materials and devices, and also present significant opportunities to tackle other heterogeneous systems using complementary theoretical and experimental studies.

cond-mat.mtrl-sci↗

arXiv2024

Insights into Chemical and Structural Order at Planar Defects in a Functional Oxide Using Multislice Electron Ptychography

Switchable order parameters in ferroic materials are essential for functional electronic devices, yet disruptions of the ordering can take the form of planar boundaries or defects that exhibit distinct properties. Characterizing the structure of these boundaries is challenging due to their confined size and three-dimensional nature. Here, a chemical anti-phase boundary in the highly ordered double perovskite \ce{Pb2MgWO6} is investigated using multislice electron ptychography. The boundary is revealed to be inclined along the electron beam direction with a finite width of chemical intermixing. Additionally, regions at and near the boundary exhibit antiferroelectric-like displacements, contrasting with the predominantly paraelectric matrix. Spatial statistics and density functional theory calculations further indicate that despite their higher energy, chemical anti-phase boundaries form due to kinetic constraints during growth, with extended antiferroelectric-like distortions induced by the chemically frustrated environment in the proximity of the boundary. The three-dimensional imaging provides critical insights into the interplay between local chemistry and the polar environment, elucidating the role of anti-phase boundaries and their associated confined structural distortions and offering new opportunities for engineering ferroic thin films.

cond-mat.mtrl-sci↗

arXiv2023

Sampling metrics for robust reconstructions in multislice ptychography: Theory and experiment

While multislice electron ptychography can provide thermal-vibration limited resolution and 3D information, it relies on the proper selection of many intertwined experimental and computational parameters. Here, we outline a theoretical basis for selecting experimental parameters to enable robust ptychographic reconstructions. We develop a series of physically informed metrics to describe the selection of experimental parameters in multislice ptychography. Image simulations are used to comprehensively evaluate the validity of these metrics over a broad range of experimental conditions. We develop two metrics, areal oversampling and Ronchigram magnification, which predict reconstruction success with high accuracy. Lastly, we validate these conclusions with experimental ptychographic data, and demonstrate close agreement between trends in simulated and experimental data. Using these metrics, we achieve experimental multislice reconstructions at a scan step of $1.0 \unit{\AA/px}$, enabling large field-of-view ($>\!18\unit{nm}$), data-efficient reconstructions. These experimental design principles enable the routine and reliable use of multislice ptychography for materials characterization.

cond-mat.mtrl-sci↗