Atomic-scale Imaging Research Articles

Intrinsic Distortion Against Jahn-Teller Distortion: A New Paradigm for High-Stability Na-Ion Layered Mn-Rich Oxide Cathodes.

Layered manganese-rich oxides (LMROs) are widely recognized as the leading cathode candidates for grid-scale sodium-ion batteries (SIBs) owing to their high specific capacities and cost benefits, but the notorious Jahn-Teller (J-T) distortion of Mn3+ always induces severe structural degradation and consequent rapid cathode failure, impeding the practical implementation of such materials. Herein, we unveil the"intrinsic distortion against J-T distortion"mechanism to effectively stabilize the layered frameworks of LMRO cathodes. The intrinsic distortion simply constructed by introducing bulk oxygen vacancies is systematically confirmed by advanced synchrotron X-ray techniques, atomic-scale imaging characterizations, and theoretical computations, which can counteract the J-T distortion during cycling due to their opposite deformation orientations. This greatly decreases and uniformizes the lattice strain within the ab plane and along the c axis of the material, thereby alleviating the P2-P'2 phase transition as well as suppressing the edge dislocation and intragranular crack formation upon repeated cycles. As a result, the tailored P2-Na0.72Mg0.1Mn0.9O2 cathode featuring intrinsic distortion delivers a considerably enhanced cycling durability (91.9% capacity retention after 500 cycles) without sacrificing the Mn3+/Mn4+ redox capacity (186.5 mAh g-1 at 0.3 C). This intrinsic distortion engineering paves a brand-new and prospective avenue toward achieving high-performance LMRO cathodes for SIBs.

Disorder-order transition-induced unusual bandgap bowing effect of tin-lead mixed perovskites.

Owing to the predominant merit of tunable bandgaps, tin-lead mixed perovskites have shown great potentials in realizing near-infrared optoelectronics and are receiving increasing attention. However, despite the merit, there is still a lack of fundamental understanding of the bandgap variation as a function of Sn/Pb ratio, mainly because the films are easy to segregate in terms of both composition and phase. Here, we report a fully stoichiometric synthesis of monocrystalline FAPb1-xSnxI3 nanocrystals as well as their atomic-scale imaging. On the basis of the systematic measurements of the monocrystalline materials, strain and Coulomb interaction-induced atomic ordering was revealed to be responsible for the unusual discontinuous bandgap jumping near x = 0.5 from the expected bowing effect. As a result, both FAPb0.6Sn0.4I3 and FAPb0.4Sn0.6I3 have the lowest bandgaps of around 1.27 electron volts, while that of FAPb0.5Sn0.5I3 is 1.33 electron volts. Correspondingly, their based light-emitting diodes can emit infrared lights with the wavelengths reaching 930 nanometers.

Discovery of collective nonjumping motions leading to Johari–Goldstein process of stress relaxation in model ionic glass

Discovery of collective nonjumping motions leading to Johari–Goldstein process of stress relaxation in model ionic glass

Combining Machine Learning Algorithms with Traditional Methods for Resolving the Atomic-Scale Dynamic Structure Reconstruction of Monolayer MoS2 in High-Resolution Transmission Electron Microscopy

Abstract High-resolution transmission electron microscopy promises rapid atomic-scale dynamic structure imaging. Yet, the precision limitations of aberration parameters and the challenge of eliminating aberrations in Cs-corrected transmission electron microscopy constrain resolution. A machine learning algorithm is developed to determine the aberration parameters with higher precision from small, lattice-periodic crystal images. The proposed algorithm is then validated with simulated HRTEM images of graphene and applied to the experimental images of a molybdenum disulfide (MoS2) monolayer with 25 variables (14 aberrations) resolved in wide ranges. Using these measured parameters, the phases of the exit-wave functions are reconstructed for each image in a focal series of MoS2 monolayers. The images were acquired due to the unexpected movement of the specimen holder. Four-dimensional data extraction reveals time-varying atomic structures and ripple. In particular, the atomic evolution of the sulfur-vacancy point and line defects, as well as the edge structure near the amorphous, are visualized as the resolution has been improved from about 1.75 Å to 0.90 Å. This method can help salvage important transmission electron microscope images and is beneficial for the images obtained from electron microscopes with average stability.

Atomic-Scale Imaging of Polymers and Precision Molecular Weight Analysis.

Polymer design requires fine control over syntheses and a thorough understanding of their macromolecular structure. Herein, near-atomic level imaging of polymers is achieved, enabling the precise determination of one of the most important macromolecular characteristics: molecular weight. By judiciously designing and synthesizing different linear metal(loid)-rich homopolymers, subnanoscale polymer imaging is achieved through annular dark field-scanning transmission electron microscopy (ADF-STEM), owing to the incorporation of high Z atoms in the side chain of the monomeric units. The molecular weight of these polymers can be precisely determined by detecting and counting their metal(loid) atoms upon ADF-STEM imaging, at sample concentrations as low as 10 μg·mL-1. Notably, a commonly used C, H, and O-containing polymer (i.e., poly(methyl acrylate)) that was thus far inaccessible at the atomic scale is derivatized to allow for subnano-level imaging, thus expanding the scope of our approach toward the atomic-level visualization of commodity polymers.

Li3VO4 mesocubes with exposed (200) facet as dendrite-free anode materials for high-safety Li-ion batteries

Li3VO4 mesocubes with exposed (200) facet as dendrite-free anode materials for high-safety Li-ion batteries

(Invited) Growth of Germanene, Stanene, Plumbene, and Their Lateral Heterostructure

The synthesis and characterization of post-graphene materials have been intensively studied with the aim of utilizing novel two-dimensional (2D) properties. Most studies adopted molecular beam epitaxy as a synthesis method of 2D materials grown on clean crystalline surfaces. In my talk, I will talk on the epitaxial growth of (1) germanene, (2) stanene, lateral heterostructure, and (3) plumbene by segregation and deposition methods[1–11]. (1) Germanene on Ag(111) thin film by segregation [1] On annealing the specimen of Ag(111) thin film grown on Ge(111)the Ge atoms segregate on the surface and germanene has been epitaxially formed on the surface. Low-energy electron diffraction clearly shows incommensurate “(1.3×1.3)”±30° spots, corresponding to a lattice constant of 0.39 nm, in perfect accord with close-up scanning tunneling microscopy (STM) images, which clearly reveal an internal honeycomb arrangement with corresponding parameter and low buckling within 0.01 nm. From the STM images, two types of protrusions, named hexagon and line, form a (7√7×7√7) ±19.1° supercell with respect to Ag(111) with a super large periodicity of 5.35 nm. (2) Stanene on Ag2Sn surface alloy by deposition [2] The lattice parameters of Ag2Sn surface alloy and free-standing stanene are close to each other. The Ag(111) easily react with Sn atoms on annealing, while the Ag2Sn surface alloy is chemically inert against the Sn atoms. Thus, the Ag2Sn surface alloy is physically and chemically ideal surface for epitaxial growth of stanene. We have successfully prepared large area planar stanene on Ag2Sn surface alloy by Sn deposition. (3) Plumbene on Pd1-xPbx(111) alloy surface by deposition and segregation [3] The bulk Pb-Pd system exists in fcc solid solution with a Pb concentration up to 10 %. The Pb atoms deposited dissolve into the Pd crystal and segregate on the surface on annealing. Through this process, plumbene is epitaxially grown on Pd1-xPbx(111) surface. The surface also exhibits a unique morphology in the STM images resembling the famous Weaire-Phelan bubble structure of the Olympic “WaterCube” in Beijing. (4) Germanene and stanene lateral heterostructure [5] We use a unique combination of atomic segregation epitaxy (ASE) and molecular beam epitaxy (MBE) for the in-situ continuous fabrication of nearly atomically precise lateral multi-junction heterostructures, respectively consisting of atom-thin germanene and stanene on a Ag(111) thin film. The STM observations down to atomic scale and low-energy electron diffraction testify that germanene and stanene sheets without intermixing are prepared simultaneously on the same terraces at wide scale; remarkably, tin and germanium atoms neither exchange their sites nor adsorb on the germanene and stanene sheets. The atomic structure of the boundary between germanene and stanene is directly derived from atomic-scale STM images, while scanning tunneling spectroscopy reveals key features of the electronic structure at the heterojunction[1,2,5]. Our innovative approach of ASE and MBE growths combined in synergy offers great flexibility for the realization of unprecedented lateral 2D heterostructures.

Ehrigite, Bi8Te3, a New Member of the Tetradymite Group

Abstract Ehrigite, Bi8Te3, is a new member of the tetradymite group and crystallizes in the trigonal crystal system (space group: , #166). Its cell dimensions are a = 4.519(6) Å, c = 65.182(24) Å, Z = 3, and V = 1152.771(7.554) Å3. Ehrigite occurs as sub-100-micron-sized grains in hedenbergite skarn from the abandoned Good Hope gold mine, Hedley district, British Columbia, Canada. The mineral and name have been approved by the IMA Commission on New Minerals and Mineral Nomenclature (proposal 2023-074). Ehrigite is compositionally and structurally distinct from hedleyite, Bi7Te3, with which it coexists. Ehrigite is opaque, with a pale gray color in reflected light. Reflectance is higher than tetradymite and slightly higher than hedleyite. It appears gray against native bismuth. The ehrigite structure consists of a single 11-atom layer visualized in atomic-scale high-angle annular dark field scanning transmission electron microscope images and further constrained from ab initio total energy calculations and structure relaxation using density functional theory using the measured parameters as input data. Scanning transmission electron microscope simulations also closely match the crystal structure model and images. Phases of the tetradymite and related modular mineral groups are well suited to visualization, indexing, and diffraction using a high-angle annular dark field scanning transmission electron microscope. The addition of density functional theory methodology to corroborate and refine structural characteristics provides a valuable approach for understanding these complex yet predictable minerals.

Machine learning assisted crystallographic reconstruction from atom probe tomographic images

Atom probe tomography (APT) is a powerful technique for three-dimensional (3D) atomic-scale imaging, enabling the accurate analysis on the compositional distribution at the nanoscale. How to accurately reconstruct crystallographic information from APT data, however, is still a great challenge due to the intrinsic nature of the APT technique. In this paper, we propose a novel approach that consists of the modified forward simulation process and the backward machine learning process to recover the tested crystal from APT data. The high-throughput forward simulations on Al single crystals of different orientations generate 10 000 original 3D images and data augmentation is implemented on the original images, resulting in 100 000 3D images. The big data allows the development of deep learning models and three deep learning algorithms of Convolutional Neural Network (CNN), Vision Transformer (ViT), and Variational Autoencoder (VAE) are used in the backward process. After training, the ViT model performs superior than the CNN and VAE models, which can recover the crystalline orientation outstandingly, as evaluated by the coefficient of determinationR2and the Mean Percent Error (MPE), viz.,R2= 0.93 and MPE = 0.43%,R2= 0.97 and MPE = 0.35%, andR2= 0.93 and MPE = 0.77% for the rotation anglesϕ,ψandθ, respectively, on the test dataset. The present work clearly demonstrates the capability of deep learning models in the recovery of the tested crystals from APT data, thereby paving the way for the further development of large artificial intelligent models of APT.

Atomic-Scale Imaging of Condensed Counterions

Atomic-Scale Imaging of Condensed Counterions

Atomic-scale imaging of laser-driven electron dynamics in solids

Resolving laser-driven electron dynamics on their natural time and length scales is essential for understanding and controlling light-induced phenomena. Capabilities to reveal these dynamics are limited by challenges in interpreting wave mixing of a driving and a probe pulse, low energy resolution at ultrashort time scales and a lack of atomic-scale resolution by standard spectroscopic techniques. Here, we demonstrate how ultrafast x-ray diffraction can access fundamental information on laser-driven electronic motion in solids. We propose a method based on subcycle-resolved x-ray-optical wave mixing that allows for a straightforward reconstruction of key properties of strong-field-induced electron dynamics with atomic spatial resolution. Namely, this technique provides both phases and amplitudes of the spatial Fourier transform of optically-induced charge distributions, their temporal behavior, and the direction of the instantaneous microscopic optically-induced electron current flow. It captures the rich microscopic structures and symmetry features of laser-driven electronic charge and current density distributions.

Design of an FPGA-Based Controller for Fast Scanning Probe Microscopy.

Atomic-scale imaging using scanning probe microscopy is a pivotal method for investigating the morphology and physico-chemical properties of nanostructured surfaces. Time resolution represents a significant limitation of this technique, as typical image acquisition times are on the order of several seconds or even a few minutes, while dynamic processes-such as surface restructuring or particle sintering, to be observed upon external stimuli such as changes in gas atmosphere or electrochemical potential-often occur within timescales shorter than a second. In this article, we present a fully redesigned field programmable gate array (FPGA)-based instrument that can be integrated into most commercially available standard scanning probe microscopes. This instrument not only significantly accelerates the acquisition of atomic-scale images by orders of magnitude but also enables the tracking of moving features such as adatoms, vacancies, or clusters across the surface ("atom tracking") due to the parallel execution of sophisticated control and acquisition algorithms and the fast exchange of data with an external processor. Each of these measurement modes requires a complex series of operations within the FPGA that are explained in detail.

Atomic-Scale Investigation of Electromigration Behavior in Cu-to-Cu Joints at High Current Density

Three-dimensional integrated circuit (3D IC) packaging offers significant advantages, such as enhanced computational efficiency through greater integration and shorter interconnection distances. The effective interconnection of layers, particularly through redistribution layer (RDL) technology, is crucial for the successful operation of 3D ICs. While copper remains the preferred material for interconnections, often in conjunction with through-silicon via (TSV) technology for chip-to-chip links, the shrinking dimensions of components present challenges. In particular, the reduction in size may lead to elevated current densities in individual joints, giving rise to issues like electromigration (EM) and potential failure. EM-induced atomic migration may lead to the formation of voids in the interconnection. The accumulation of voids to a critical point may result in an open circuit in the joints, significantly impacting the conductor's reliability. This work delves into the micro-scale aspects of these challenges, complementing previous macroscopic investigations. We aim to elucidate the behavioral mechanisms through atomic-scale observations, employing an in-situ high-resolution transmission electron microscope (in-situ HRTEM) to observe atomic-scale images of EM. The insights gained from this work not only contribute to the academic understanding of industry challenges but hold potential applications in real-world manufacturing processes. Fig. 1. (a) Schematic diagram of TEM sample preparation. (b) Cross-sectional HRTEM image of copper bonding. (c, d) TEM images showing voids expansion at bonding interface. Figure 1

Atomic Scale Imaging of Complex Oxide Interfaces

Atomic Scale Imaging of Complex Oxide Interfaces

Probing Defectivity Beneath the Hydrocarbon Blanket in 2D hBN Using TEM-EELS.

The controlled creation and manipulation of defects in 2D materials has become increasingly popular as a means to design and tune new material functionalities. However, defect characterization by direct atomic-scale imaging is often severely limited by surface contamination due to a blanket of hydrocarbons. Thus, analysis techniques that can characterize atomic-scale defects despite the contamination layer are advantageous. In this work, we take inspiration from X-ray absorption spectroscopy and use broad-beam electron energy loss spectroscopy (EELS) to characterize defect structures in 2D hexagonal boron nitride (hBN) based on averaged fine structure in the boron K-edge. Since EELS is performed in a transmission electron microscope (TEM), imaging can be performed in-situ to assess contamination levels and other factors such as tears in the fragile 2D sheets, which can affect the spectroscopic analysis. We demonstrate the TEM-EELS technique for 2D hBN samples irradiated with different ion types and doses, finding spectral signatures indicative of boron-oxygen bonding that can be used as a measure of sample defectiveness depending on the ion beam treatment. We propose that even in cases where surface contamination has been mitigated, the averaging-based TEM-EELS technique can be useful for efficient sample surveys to support atomically resolved EELS experiments.

Reinforced BiOBr for visible-light-driven nitrogen fixation: A synergistic effect of cocatalyst and oxygen vacancies

Reinforced BiOBr for visible-light-driven nitrogen fixation: A synergistic effect of cocatalyst and oxygen vacancies

Clogauite, PbBi4Te4S3, a new member of the aleksite series

AbstractClogauite, ideally PbBi4Te4S3 is the new n = 1 member of the aleksite series, PbnBi4Te4Sn+2, where n is the homologue number. Clogauite is named from the type locality, the Clogau gold mine, Dolgellau Gold belt, Gwynedd, North Wales, United Kingdom. The mineral and name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2023–062). The aleksite series is an accretional homologous series in which each member is derived from the same 5-atom tetradymite archetype. Clogauite crystallises in the trigonal crystal system (space group: P$\bar{3}$m1, #164). Three distinct polytypes of clogauite are recognised, corresponding to identical chemistry but different layer sequences, expressed as (57), (5559) and (557.559), respectively, in reference to the number of atoms in individual layer sequences. These are clogauite-12H, a = 4.277(4) Å, c = 23.46(14) Å, V = 371.598 Å3 and Z = 1; clogauite-24H, a = 4.278(4) Å, c = 46.88(31) Å, V = 743.053 Å3 and Z = 2; and clogauite-36H, a = 4.278(4) Å, c = 70.36(32) Å, V = 1115.283 Å3 and Z = 3. Clogauite is opaque, with a pale grey colour in reflected light. Reflectance is higher than tetradymite or galena. Bireflectance and anisotropy are strong. Structural data were determined from measurement of atomic-scale HAADF STEM imaging showing the internal arrangement of component atoms and characteristic selected area electron diffraction patterns for each polytype. The structures were then further constrained from ab initio total energy calculations and structure relaxation using density functional theory (DFT) using the measured parameters as input data. The relaxed crystal structure for each polytype was modelled to generate crystallographic information files (cif). STEM and electron diffraction simulations based on the crystallographic information data obtained from the DFT calculations show an excellent match to the empirical measurements.

Low-frequency conductivity of low wear high-entropy alloys

High-entropy alloys (HEAs) provide new research avenues for alloy combinations in the periodic table, opening numerous possibilities in novel-alloy applications. However, their electrical characteristics have been relatively underexplored. The challenge in establishing an HEA electrical conductivity model lies in the changes in electronic characteristics caused by lattice distortion and complexity of nanostructures. Here we show a low-frequency electrical conductivity model for the Nb-Mo-Ta-W HEA system. The cocktail effect is found to explain trends in electrical-conductivity changes in HEAs, while the magnitude of the reduction is understood by the calculated plasma frequency, free electron density, and measured relaxation time by terahertz spectroscopy. As a result, the refractory HEA Nb15Mo35Ta15W35 thin film exhibits both high hardness and excellent conductivity. This combination of Nb15Mo35Ta15W35 makes it suitable for applications in atomic force microscopy probe coating, significantly improving their wear resistance and atomic-scale image resolution.

Solute micro-segregation profile and associated precipitation in cast Al-Mg-Si alloy

ABSTRACT The micro-segregation in the as-cast AA6082 aluminium alloy were investigated across a range of length scales using a combination of analytical electron microscopes. It is found that the micro-segregation bands form an inter-connected network following grain boundaries and inter-dendritic channels. The micro-segregation can be divided into major micro-segregation and minor micro-segregation; the former is mainly on the grain boundaries consisting of iron-bearing intermetallic; the latter occurs both, along the grain boundaries and inter-dendritic channels, consisting mainly of Mg and Si alloying elements. The atomic-scale imaging reveals that in the minor-segregation bands, the supersaturated solute concertation has formed precipitates that had either nucleated heterogeneously on the dislocation network or homogeneously inside the aluminium matrix. The heterogeneously nucleated precipitates in the dislocation lines are composed of a mixture of phases down the precipitation sequence meanwhile, the homogenously grown ones are discrete phases that appear at the early stages of the precipitation sequence.

Disruption of polar order in lead zirconate titanate by composition-modulated artificial superlattice

Lead zirconate titanate (Pb (Zrx, Ti1−x)O3: PZT) is a well-known ferroelectric compound, in which long-range polar order is usually developed. In the present study, it was clarified by distortion-corrected atomic-scale scanning transmission electron microscopy imaging that long-range polar order is disrupted in PZT by utilizing composition-modulated superlattice. Shape of unit cell was unusual both in the Pb(Zr0.65Ti0.35)O3 (PZT65) and Pb(Zr0.30Ti0.70)O3 (PZT30) layers, which was due to mutual in-plane lattice constraint. By taking account of this, first-principles calculations clarified that multiple directions can be energetically favorable for lead-ion displacement, which explains a reason why long-range polar order was disrupted.