Atomic-scale Imaging Research Articles

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

Photocatalytic nitrogen fixation is a promising long-term strategy for NH3 synthesis, with the development of effective and durable photocatalysts being crucial for achieving high-efficiency N2 to NH3 conversion. In this study, we employed vacancy and interface engineering to create bismuth (Bi) nanoparticles on hierarchical oxygen-deficient BiOBr microspheres using a one-step solvothermal approach. These Bi-decorated BiOBr microspheres, featuring oxygen vacancies, achieved a high photocatalytic ammonia synthesis rate of 222.3 μmol·g−1·h−1 in pure water under visible light irradiation, which is 3.25 times higher than that of the original BiOBr. Atomic-scale images of the interface between the defective regions of BiOBr and the Bi cocatalyst and several other material characterizations confirmed that the enhanced photoreduction activity of Bi/BiOBr is due to the synergistic effects of the metal Bi and the oxygen vacancies. These results present a straightforward and practical method for designing efficient photocatalysts for nitrogen fixation.

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.

Ingenious Architecture and Coloration Generation in Enamel of Rodent Teeth.

Teeth exemplify architectures comprising an interplay of inorganic and organic constituents, resulting in sophisticated natural composites. Rodents (Rodentia) showcase extraordinary adaptations, with their continuously growing incisors surpassing human teeth in functional and structural optimizations. In this study, employing state-of-the-art direct atomic-scale imaging and nanoscale spectroscopies, we present compelling evidence that the release of material from ameloblasts and the subsequent formation of iron-rich enamel and surface layers in the constantly growing incisors of rodents are complex orchestrated processes, intricately regulated and independent of environmental factors. The synergistic fusion of three-dimensional tomography and imaging techniques of etched rodent́s enamel unveils a direct correlation between the presence of pockets infused with ferrihydrite-like material and the acid resistant properties exhibited by the iron-rich enamel, fortifying it as an efficient protective shield. Moreover, observations using optical microscopy shed light on the role of iron-rich enamel as a microstructural element that acts as a path for color transmission, although the native color remains indistinguishable from that of regular enamel, challenging the prevailing paradigms. The redefinition of "pigmented enamel" to encompass ferrihydrite-like infusion in rodent incisors reshapes our perception of incisor microstructure and color generation. The functional significance of acid-resistant iron-rich enamel and the understanding of the underlying coloration mechanism in rodent incisors have far-reaching implications for human health, development of potentially groundbreaking dental materials, and restorative dentistry. These findings enable the creation of an entirely different class of dental biomaterials with enhanced properties, inspired by the ingenious designs found in nature.

Atomic-Scale Insights into Flow-Accelerated Corrosion of Carbon Steel

The role of flow velocity on the formation and dissolution of oxides on SA106Gr.B carbon steel was investigated at both microscopic and atomic scales. In static water, a compact oxide layer with highly faceted magnetite particles was formed. Atomic-scale transmission electron microscopy images of such a layer revealed highly ordered and parallel lattice fringes, indicating that the oxide had very high crystallinity and minimal lattice defects. In contrast, turbulent water prompted the creation of a porous oxide layer consisting of amorphous magnetite particles. Here, numerous mismatched lattice fringes were observed, indicating a prevalence of point defects within the oxide structure. These differences in oxide properties are attributed to hydrodynamic shear stress induced by turbulent flow. These findings provide atomic-level insights into how carbon steel corrosion accelerates in fast-flowing water.

Seeing is believing: Correlating optoelectronic functionality with atomic scale imaging of single semiconductor nanocrystals.

A unique on-chip method for the direct correlation of optical properties, with atomic-scale chemical-structural characteristics for a single quantum dot (QD), is developed and utilized in various examples. This is based on performing single QD optical characterization on a modified glass substrate, followed by the extraction of the relevant region of interest by focused-ion-beam-scanning electron microscope processing into a lamella for high resolution scanning transmission electron microscopy (STEM) characterization with atomic scale resolution. The direct correlation of the optical response under an electric field with STEM analysis of the same particle allows addressing several single particle phenomena: first, the direct correlation of single QD photoluminescence (PL) polarization and its response to the external field with the QD crystal lattice alignment, so far inferred indirectly; second, the identification of unique yet rare few-QD assemblies, correlated directly with their special spectroscopic optical characteristics, serving as a guide for future designed assemblies; and third, the study on the effect of metal island growth on the PL behavior of hybrid semiconductor-metal nanoparticles, with relevance for their possible functionality in photocatalysis. This work, therefore, establishes the use of the direct on-chip optical-structural correlation method for numerous scenarios and timely questions in the field of QD research.

Intermixing of iron and cobalt with oxygen-rich magnesium oxide in CoFeB/MgO/CoFeB magnetic tunneling junctions

Atomic-scale spectroscopic imaging of sputtered magnetic tunnel junction structures with a thick oxygen-rich MgO barrier reveals the diffusion of iron and cobalt into the MgO barrier from CoFeB electrodes. First principles calculations are performed to (1) confirm that Fe diffusion through Mg vacancies is energetically favorable, (2) quantify the reduction of interfacial perpendicular magnetic anisotropy due to Fe diffusion into MgO, and (3) predict that the presence of Fe impurities in MgO causes an increased leakage and a tunneling magnetoresistance decrease. Through the chemical shift of the Fe L3 edge and the peak ratio Fe L3/Fe L2 measured by electron energy loss spectroscopy, we suggest that, within MgO, iron with mixed oxidation state Fe2+ and Fe3+ or higher is found in the as-grown structure, which is reduced by annealing to Fe2+. These results indicate that the stoichiometry of as-deposited MgO barrier layers plays an important role in controlling the microstructure and optimizing the performance of magnetic tunnel junctions.

Atomic-Scale Imaging of Clay Mineral Nanosheets and Their Supramolecular Complexes through Electron Microscopy: A Supramolecular Chemist's Perspective.

Recent advancements in electron microscopy techniques have revolutionized the ability to directly visualize and understand the intricate world of supramolecular chemistry. This paper provides a concise overview of a study delving into the atomic-scale imaging of monolayer clay mineral nanosheets and their associated supramolecular complexes. The imaging is conducted by harnessing the power of aberration-corrected scanning transmission electron microscopy (STEM). Clay mineral nanosheets, with their anionic charge and ultrathin thickness (of 1 nm), serve as a stable Coulombic host material for cationic guest molecules through electrostatic interactions, facilitating exceptional stability and control during observation. By incorporation of heavy-metal atom markers coordinated within the target molecules, high-angle annular dark field STEM enables a clear visualization of these supramolecular complexes. This approach helps to overcome the limitations of graphene-based systems and expands the possibilities of atomic-scale imaging of nonperiodic molecular assemblies formed by weak supramolecular interactions. The fusion of electron microscopy techniques with the principles of supramolecular and material chemistry offers exciting opportunities for studying the structure, behavior, and properties of complex supramolecular systems. It sheds light on the intricate molecular architectures and design principles governing these systems. This study showcases the immense potential of electron microscopy in supramolecular chemistry and invites researchers from various disciplines to explore the transformative possibilities of atomic-scale imaging in the field.

Relationship between molecular structure and corrugations in self-assembled polypeptoid nanosheets revealed by cryogenic electron microscopy

Designing conformationally dynamic molecules that self-assemble into predictable nanostructures remains an important unmet challenge. This paper describes how atomic-scale cryogenic transmission electron microscopy (cryo-TEM) can be used to explore the relationship between molecular structure and self-assembly of block copolymers. We examined sheetlike micelles formed in water using a series of diblock copolypeptoids with the same hydrophilic block and three distinct crystalline hydrophobic blocks. Our cryo-TEM images revealed all the structures share nansoscale features, but differ in their intermolecular packing geometries. Different molecular arrangements, parallel and antiparallel V-shaped crystal motifs, were revealed by two-dimensional atomic-scale through-plane images. However, images from tilted samples revealed an unexpected feature when the hydrophobic polypeptoid block comprised phenyl rings with substituted bromine atoms at the para position. The nanosheets contained atomic-scale corrugations that were absent in the other systems which comprised unsubstituted aliphatic and aromatic side chains. We hypothesize that these corrugations are due to the dipolar characteristics of the brominated phenyl group and interactions between this group and water molecules. Published by the American Physical Society 2024

Atomic-Scale Time-Resolved Imaging of Krypton Dimers, Chains and Transition to a One-Dimensional Gas.

Single-atom dynamics of noble-gas elements have been investigated using time-resolved transmission electron microscopy (TEM), with direct observation providing for a deeper understanding of chemical bonding, reactivity, and states of matter at the nanoscale. We report on a nanoscale system consisting of endohedral fullerenes encapsulated within single-walled carbon nanotubes ((Kr@C60)@SWCNT), capable of the delivery and release of krypton atoms on-demand, via coalescence of host fullerene cages under the action of the electron beam (in situ) or heat (ex situ). The state and dynamics of Kr atoms were investigated by energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS). Kr atom positions were measured precisely using aberration-corrected high-resolution TEM (AC-HRTEM), aberration-corrected scanning TEM (AC-STEM), and single-atom spectroscopic imaging (STEM-EELS). The electron beam drove the formation of 2Kr@C120 capsules, in which van der Waals Kr2 and transient covalent [Kr2]+ bonding states were identified. Thermal coalescence led to the formation of longer coalesced nested nanotubes containing more loosely bound Krn chains (n = 3-6). In some instances, delocalization of Kr atomic positions was confirmed by STEM analysis as the transition to a one-dimensional (1D) gas, as Kr atoms were constrained to only one degree of translational freedom within long, well-annealed, nested nanotubes. Such nested nanotube structures were investigated by Raman spectroscopy. This material represents a highly compressed and dimensionally constrained 1D gas stable under ambient conditions. Direct atomic-scale imaging has revealed elusive bonding states and a previously unseen 1D gaseous state of matter of this noble gas element, demonstrating TEM to be a powerful tool in the discovery of chemistry at the single-atom level.

Flexoelectric polarizing and control of a ferromagnetic metal

Electric polarization is well defined only in insulators not metals, and there is no general scheme to induce and control bulk polarity in metals. Here we circumvent this limitation by utilizing a pseudo-electric field generated by inhomogeneous lattice strain, namely a flexoelectric field, as a means of polarizing and controlling a metal. Using heteroepitaxy and atomic-scale imaging, we show that flexoelectric fields polarize the bulk of an otherwise centrosymmetric metal SrRuO3, with off-centre displacements of Ru ions. This further impacts the electronic bands and lattice anisotropy of the flexo-polar SrRuO3, potentially leading to an enhancement of electron correlation, ferromagnetism and its anisotropy. Beyond conventional electric fields, flexoelectric fields may be used to create and control electronic states through pure atomic displacements.

Advances in Atomic Time Scale Imaging with a Fine Intrinsic Spatial Resolution

Atomic time scale imaging, opening a new era for studying dynamics in microcosmos, is presently attracting immense research interest on the global level due to its powerful ability. On the atom level, physics, chemistry, and biology are identical for researching atom motion and atomic state change. The light possesses twoness, the information carrier and the research resource. The most fundamental principle of this imaging is that light records the event-modulated light field by itself, so-called all-optical imaging. This paper can answer what is the essential standard to develop and evaluate atomic time scale imaging, what is the optimal imaging system, and what are the typical techniques to implement this imaging, up to now. At present, the best record in the experiment, made by multistage optical parametric amplification (MOPA), is realizing 50-fs resolved optical imaging with a spatial resolution of ~83 lp/mm at an effective framing rate of 15 × 10 12 fps for recording an ultrafast optical lattice with its rotating speed up to 13.5 × 10 12 rad/s.