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Abstract Scaling ferroelectrics to nanometer thicknesses remains a central challenge for low-power, nonvolatile electronics, as leakage currents increasingly dominate at reduced dimensions. Alkali-based, lead-free ferroelectrics offer an environmentally sustainable alternative to lead-based systems, yet their scaling is severely limited by leakage arising from volatile alkali constituents. Here, we show that this intrinsic limitation can be transformed into an advantageous degree of freedom through defect engineering. By precisely modulating alkali deficiency during thin-film synthesis, we engineer clustered defect complexes that function as deep trap states, strongly suppressing leakage and enabling robust ferroelectric operation in ultrathin films down to the sub-10 nm regime at voltages below 100 mV. Our results establish defect-enabled scaling as a viable pathway for advancing environmentally benign ferroelectrics toward ultra-low-power, nonvolatile electronic technologies. 

Abstract Atomic-resolution imaging of battery materials is critical for identification of local defects and structural variations, which are tied to battery performance. However, since battery materials are, by design, optimized to allow ion motion in response to an applied electric field, they are also very sensitive to radiation damage by an electron beam. Image resolution is therefore severely constrained by the dose applied. Here, we show that multislice electron ptychography (MEP) can provide sub-ångström lateral resolution images of both light and heavy elements of a Li-ion battery cathode, along with nanometer-scale depth information and greater dose efficiency than conventional electron microscopy methods. Using the depth-sectioning capability of MEP, we have been able to obtain direct visualizations of Li vacancy clusters, atom column by atom column, in LixNi0.33Mn0.33Co0.33O2 (NMC111) cathodes. This capability to track Li distributions will be valuable in understanding, informing, and optimizing electrode material design for ion storage and transfer. 

Abstract Gallium nitride (GaN) and aluminum nitride (AlN) host high-density two-dimensional electron and hole gases in undoped GaN quantum wells, created by built-in polarization fields and favorable band offsets. These interfacial states are essential for many high-power and high-frequency devices, yet momentum-resolved measurements (particularly under applied bias) remain rare due to two challenges: (i) the surface sensitivity of conventional vacuum-ultraviolet ARPES, which cannot probe deeply buried states, and (ii) the difficulty of implementing electrostatic gating in semiconductor heterostructures due to leakage currents. Here, we use soft X-ray ARPES to overcome the first challenge, directly accessing quantized states several nanometers below the surface in GaN/AlN heterostructures and relating their subband dispersions to transport characteristics. As a precursor to gated ARPES, we employ controlled oxygen adsorption to chemically tune the potential and track the resulting band shifts. This approach opens a pathway toward fully gate-tunable, momentum-resolved studies of buried states in wide-bandgap devices. 

ABSTRACT Resonant tunneling is a quantum mechanical effect that enables electrons to traverse classically forbidden regions of space. The engineering of this quantum effect in wide‐bandgap semiconductors promises important technological benefits as it seamlessly combines ultra‐fast electron transport dynamics with superior power‐handling capabilities. Here, we report the first realization of highly coherent electronic quantum interference and resonant tunneling injection in wide‐bandgap triple‐barrier heterostructures. Enabled by the high structural quality of the GaN/AlN triple‐barrier active region, we observe multiple resonant tunneling peaks and negative differential conductance at room temperature. The robustness of the inter‐well resonant tunneling current is experimentally confirmed via temperature‐dependent electronic transport and the generation of electrically tunable microwave oscillations. These results represent a stepping stone in the engineering of intersubband tunneling transport in wide‐bandgap III‐nitride semiconductors, raising hopes for the realization of intersubband optical amplification and frequency‐modulated resonant tunneling oscillators. 

Abstract High-resolution transmission electron microscopy (HRTEM) is an important method for imaging beam sensitive materials often under cryo conditions. Electron ptychography in the scanning transmission electron microscope (STEM) has been shown to reconstruct low-noise phase data at a reduced fluence for such materials. This raises the question of whether ptychography or HRTEM provides a more fluence-efficient imaging technique. Even though the transfer function is a common metric for evaluating the performance of an imaging method, it only describes the signal transfer with respect to spatial frequency, irrespective of the noise transfer. It can also not be well defined for methods, such as ptychography, that use an algorithm to form the final image. Here we apply the concept of detective quantum efficiency (DQE) to electron microscopy as a fluence independent and sample independent measure of technique performance. We find that, for a weak-phase object, ptychography can never reach the efficiency of a perfect Zernike phase imaging microscope but that ptychography is more robust to partial coherence. 

Abstract Next-generation semiconductor devices are adopting three-dimensional (3D) architectures with feature sizes in the few-nanometer regime, creating a need for atomic-scale metrology to identify and resolve performance-limiting fabrication challenges. X-ray methods provide 3D information but lack atomic resolution, while conventional electron microscopy offers limited depth sensitivity. Here we show how multislice electron ptychography, a computational microscopy technique with sub-Ångström lateral and nanometer-scale depth resolution, enables 3D imaging of buried device structures. We image prototype gate-all-around transistors and directly quantify roughness, strain, and defects at the interface of the 3D gate oxide wrapped around the channel. We find that silicon in the 5-nm-thick channel relaxes away from the interfaces, leaving only ~60% of atoms in a bulk-like structure. From a single dataset, ptychography provides quantitative metrology of atomic-scale interface roughness in 3D, previously accessible only through indirect inference, along with strain and other structural parameters needed for device modeling and process development. 

Abstract Tilt-corrected imaging methods in four-dimensional scanning transmission electron microscopy (4D-STEM) have recently emerged as a new class of direct ptychography methods that are especially useful at low dose. The operation of tilt correction unfolds the contrast transfer functions (CTFs) of the virtual bright-field images and retains coherence by correcting aberration-induced spatial shifts. By performing summation or subtraction of the tilt-corrected images, the real or imaginary parts of the complex phase-contrast transfer functions are recovered, producing a tilt-corrected bright field image (tcBF) or a differential phase contrast image (tcDPC). However, the CTF can be strongly damped by the introduction of higher-order aberrations than defocus. In this paper, we show how aberration-corrected bright-field imaging (acBF), which combines tcBF and tcDPC, enables continuously-nonzero contrast transfer within the information limit, even in the presence of higher-order aberrations. In fact, higher-order aberrations can be beneficial, removing oscillations from the acBF CTF. We demonstrate acBF on both simulated and experimental data, showing it produces superior performance to tcBF or DPC methods alone, and discuss its limitations, including estimates for the number of pixels needed on the detector. 

ABSTRACT A systematic study of the effect of film thickness on the stability of the spin cycloid in BiFeO₃grown epitaxially on TbScO₃(110) substrates reveals a complex evolution of both the crystal and ferroelectric domain structures as well as the magnetic order. For films thicker than ∼5 nm, the structure remains rhombohedral, but the lattice mismatch is accommodated by the formation of 71° ferroelastic‐closure domains, rather than misfit dislocations, followed by the formation of 109° domains. For films ≲ 5 nm, a mixed‐phase coexistence of a polar, rhombohedral‐like (R3c) phase and an antipolar (Pnma) phase is observed. Scanning nitrogen‐vacancy magnetometry reveals a change in the propagation vector of the spin cycloid with thickness. It evolves from parallel to the ferroelectric domains for 50 nm thick samples and thicker and reorients to perpendicular to the ferroelectric domains for intermediate thicknesses, and vanishes for films ≲ 5 nm, which is reflected in macroscopic spin transport measurements and supported by the simulations. Ultimately, this work provides a deep understanding of the role of film thickness and electrostatic boundary conditions on the ferroelectric domain configuration and, therefore on the spin cycloid to design the device with electric field control antiferromagnetism. 

ABSTRACT Magnetic skyrmions are topologically protected spin states that hold promise for shaping the future of electronics. Despite impressive progress in skyrmion research, the microscopic mechanisms underlying skyrmion phase transitions at specific temperatures and magnetic fields remain elusive. In this work, we systematically study the isostructural centrosymmetric magnets GdRu₂X₂(X = Si and Ge) and the role of X‐porbitals in modifying magnetic exchange interactions. Electronic structure and exchange interaction evaluations reveal that the more extended Ge‐4pversus Si‐3porbitals enhance competing exchange interactions in GdRu₂Ge₂, thereby manifesting the evolution condition of skyrmions in GdRu₂X₂. GdRu₂Ge₂single crystals exhibit two high‐entropy regions associated with skyrmion phases at 0.9 T ≤µ₀H≤ 1.2 T and 1.3 T ≤µ₀H≤ 1.7 T, 2 K ≤T≤ 30 K—lower field and higher temperature conditions than those in the Si counterpart. Transport measurements reveal the topological Hall effect, validating the topologically nontrivial spin textures and Berry curvature. Our work bridges the gap between skyrmion discovery and material design by demonstrating, for the first time, how atomic‐scale control of exchange interactions enables tunable skyrmion phase transitions, making a significant step toward stabilizing skyrmions at desired temperatures and magnetic fields. 

Abstract The discovery of high-temperature superconductivity in bulk La₃Ni₂O₇under high hydrostatic pressure^1–4and biaxial compression in epitaxial thin films^5–8has generated substantial interest in understanding the interplay between atomic and electronic structure in these compounds. Subtle changes in the nickel–oxygen bonding environment are thought to be key drivers for stabilizing superconductivity, but specific details of which bonds and which modifications are most relevant remain unresolved so far. Although direct, atomic-scale structural characterization under hydrostatic pressure is beyond present experimental capabilities, static stabilization of strained La₃Ni₂O₇films provides a platform well suited to investigation with new picometre-resolution electron microscopy methods. Here we use multislice electron ptychography (MEP)^9,10to directly measure the atomic-scale structural evolution of La₃Ni₂O₇thin films across a wide range of biaxial strains tuned by substrate choice. By resolving both the cation and oxygen sublattices, we study the strain-dependent evolution of atomic bonds, providing the opportunity to isolate and disentangle the effects of specific structural motifs for stabilizing superconductivity. We identify the lifting of crystalline symmetry through modification of the nickel–oxygen octahedral distortions under compressive strain as a key structural ingredient for superconductivity and identify in-plane lattice compression as a common attribute between bulk and thin-film superconductivity. Building on the detailed structures obtained by MEP, we introduce a theoretical framework to disentangle coupled structural distortions in corner-sharing octahedra¹¹, which suggest that both known superconducting geometries of La₃Ni₂O₇(hydrostatic pressure and compressive strain) suppress localt_2gorbital mixing in the low-energy Ni bands by raising the octahedral symmetry.