arXiv subjects

Penghan Lu

Publications and source records attributed to Penghan Lu.

3 recordsLinked to original sources

arXiv2026

Depth-Resolved Evolution of Buried Polar Topologies in a PbTiO3/SrTiO3 Superlattice

Polar topologies in complex oxides gives rise to a rich spectrum of emergent functionalities and are fundamentally governed by three-dimensional (3D) atomic structures. However, direct experimental determination of buried 3D polar configurations remains a longstanding challenge because conventional (scanning) transmission electron microscopy ((S)TEM) provides primarily projected structural information with limited depth sensitivity. Here, we combine depth-sectioning low-angle annular dark-field (LAADF) STEM, high-angle ADF (HAADF) STEM, and multislice electron ptychography (MEP) to directly visualize the depth-dependent atomic structure and polarization topology in a PTO/STO superlattice. Depth-sectioning STEM reveals pronounced focal-depth-dependent contrast variations and apparent splitting of Pb atomic columns, indicating significant structural heterogeneity along the beam direction. MEP reconstruction simultaneously resolves the Pb, Ti, and O sublattices with nanometer-scale depth resolution, enabling quantitative mapping of atomic displacements throughout the reconstructed volume. The resulting 3D atomic model reveals substantial depth-dependent displacements of Pb, Ti, and O atoms and a corresponding evolution of the polarization topology. Vortex-like polarization structures are observed near the specimen surfaces but become strongly suppressed within the interior, where distinct polarization configurations emerge. These findings show that polarization patterns observed in conventional projection images can arise from the superposition of multiple depth-dependent polar states and may obscure the underlying 3D polarization texture. Our findings establish a direct experimental link between local atomic displacements and depth-dependent polarization topology, opening new opportunities for investigating and engineering buried functional states in complex oxide nanostructures.

cond-mat.mtrl-sci↗

arXiv2025

Electron beam precession for a serial crystallography experiment in a TEM

During the last few years, serial electron crystallography (Serial Electron Diffraction, SerialED) has been gaining attention for the structure determination of crystalline compounds that are sensitive to the irradiation of the electron beam. By recording a single electron diffraction pattern per crystal, indexing hundreds or even thousands of measured particles, and merging the reflection intensities of the successfully indexed patterns, one can retrieve crystal structure models with strongly mitigated beam damage contributions. However, one of the technique's bottlenecks is the need to collect that many diffraction patterns, which, done in an automated way, results in low indexing rates. This work demonstrates how to overcome this limitation by performing the serial crystallography experiment following a semi-automated routine with a precessed electron beam (Serial Precession Electron Diffraction, SerialPED). The precession movement increases the number of reflections present in the diffraction patterns and dynamical effects related to specific orientations of the crystals with respect to the electron beam are smoothed out. This leads to more uniform reflection intensities across the serial dataset and a smaller number of patterns are required to merge the reflection intensities for good statistics. Furthermore, structure refinements based on the dynamical diffraction theory become accessible, providing a novel approach for more accurate structure models. In this context, the use of beam precession is presented as an advantageous tool for serial electron crystallography as it enables reliable crystal structure analysis with a lower amount of diffraction data.

cond-mat.mtrl-sci↗

arXiv2025

Correlative and in situ microscopy investigation of phase transformation, crystal growth and degradation of antimony sulfide thin films

Antimony sulfide (Sb$_2$S$_3$), a compound of earth-abundant elements with highly anisotropic, quasi-layered crystal structure, triggered growing interest as a solar absorber in photovoltaics and as a phase change material in memory devices, yet challenges remain in achieving high-quality thin films with controlled nucleation and growth for optimal performance. Here, we investigate the phase transformation, crystal structure and properties, growth and degradation of atomic layer deposited Sb$_2$S$_3$ thin films using in situ TEM and correlative ex situ analysis. The as-deposited amorphous films crystallized at 243{\deg}C, forming grains with an [100] out-of-plane texture and developed into tens to hundreds of micrometer, leaves-shaped grains. Introducing an ultra-thin ZnS interfacial layer increased nucleation density, and resulted in a few micrometer-sized, more uniform grains while retaining the overall [100] texture. In situ observations and subsequent crystal orientation analysis with cutting-edge 4D-STEM and EBSD revealed that the grains grew faster along the [010] ribbon direction and that the bare films underwent early-stage degradation, forming holes in amorphous regions during annealing. The ZnS interlayer mitigated degradation, stabilizing the films and improving their uniformity. These findings offer valuable insights for optimizing Sb$_2$S$_3$ thin films for applications both as solar cell materials and phase change materials.

cond-mat.mtrl-sci↗