Atomic Arrangement Research Articles

Rapid High-Temperature Liquid Shock Synthesis of High-Entropy Alloys for Hydrogen Evolution Reaction.

High-entropy-alloy nanoparticles (HEA-NPs) show great potential as electrocatalysts for water splitting, fuel cells, CO2 conversion, etc. However, fine-tuning the surface, morphology, structure, and crystal phase of HEA remains a great challenge. Here, the high-temperature liquid shock (HTLS) technique is applied to produce HEA-NPs, e.g., PtCoNiRuIr HEA-NPs, with tunable elemental components, ultrafine particle size, controlled crystal phases, and lattice strains. HTLS directly applied Joule heating on the liquid mixture of metal precursors, capping agents, and reducing agents, which is feasible for controlling the morphology and structure such as the atomic arrangement of the resulting products, thereby facilitating the rationally designed nanocatalysts. Impressively, the as-obtained PtCoNiRuIr HEA-NPs delivered superior activity and long-term stability for the hydrogen evolution reaction (HER), with low overpotentials at 10 mA cm-2 and 1 A cm-2 of only 18 and 408 mV, respectively, and 10000 CV stable cycles in 0.5 M H2SO4. Furthermore, in the near future, by combining the HTLS method with artificial intelligence (AI) and theoretical calculations, it is promising to provide an advanced platform for the high-throughput synthesis of HEA nanocatalysts with optimized performance for various energy applications, which is of great significance for achieving a carbon-neutral society with an effective and environmentally friendly energy system.

Unified Interpretations of Two Kinds of Needle-Shaped Precipitates Using Transmission Electron Microscopy and Small-Angle Neutron Scattering in Aged Al-Mg2Si(-Cu) Alloys.

This study investigates the nanostructural properties of pseudo-binary Al-1.0Mg2Si (mass%) alloys with and without 0.5Cu using transmission electron microscopy (TEM) and small-angle neutron scattering (SANS). The TEM results show that both alloys exhibit extra electron diffraction spots related to MgSiMg second clusters at peak-aged conditions. High-resolution TEM images have revealed that the second cluster exists as a needle-shaped precipitate that is shorter and thicker than the β″ phase. We found that the second cluster, which we referred to as the R phase in this paper, is more likely to form partially along the longitudinal axis of a random-type precipitate. Thus, the atomic arrangement in the random-type precipitate is not completely random. SANS is used to quantify the size and volume fraction of the observed needle-shaped precipitates since the R phase is difficult to observe with TEM. The R phase forms even in the Cu-free alloy, but the volume fraction is low, and the growth and formation are retarded near the peak-aged conditions. Undoubtedly, the Cu addition has the effect of stabilizing the growth of the R phase and also promoting its formation. Therefore, the R phase also contributes to the increase in hardness at both under- and peak-aged conditions in the Cu-containing alloy in addition to the strengthening β″ phases.

Tailoring Local Chemical Ordering via Elemental Tuning in High-Entropy Alloys.

Due to the large multi-elemental space desired for property screening and optimization, high-entropy alloys (HEAs) hold greater potential over conventional alloys for a range of applications, such as structural materials, energy conversion, and catalysis. However, the relationship between the HEA composition and its local structural/elemental configuration is not well understood, particularly in noble-metal-based HEA nanomaterials, hindering the design and development of nano-HEAs in energy conversion and catalysis applications. Herein, we determined precise atomic-level structural and elemental arrangements in model HEAs composed of RhPtPdFeCo and RuPtPdFeCo to unveil their local characteristics. Notably, by changing just one constituent element in the HEA (Rh to Ru), we found dramatic changes in the elemental arrangement from complete random mixing to a local single elemental ordering feature. Additionally, we demonstrate that the local ordering in RuPtPdFeCo can be further controlled by varying the Ru concentration, allowing us to toggle between local Ru clustering and distinct heterostructures in multicomponent systems. Overall, our study presents a practical approach for manipulating local atomic structures and elemental arrangements in noble-metal-based HEA systems, which could provide in-depth knowledge to mechanistically understand the functionality of noble-metal-based HEA nanomaterials in practical applications.

Optimization radiation shielding properties of aluminum-based spinel minerals through the crystal tetrahedral and octahedral voids and their ions composition

In this research paper, we delve into the influence of crystal structure, void volumes and their ionic composition along with the atomic packing factor on the radiation attenuation properties of Al-based spinel compounds. The study investigates various Al-spinel chemical compositions explores their applications in radiation shielding. Analyzing mass attenuation coefficient (MAC) of six spinel minerals across different energy regions, we observe specific trends in scattering processes with the following sequential order: MACPleonaste > MACGahnite > MACHercynite > MACGalaxite > MACCeylonite > MACSpinel. The results demonstrated that the MAC values were influenced by the spinel chemical composition, crystal structure, and atomic arrangement in the lattice. Furthermore, the correlation between MAC values and the tetrahedral volume (Vtet), octahedral volume (Vocta), and the ratio of void volumes to the unit cell volume (R) was examined. Optimal void volumes and divalent and trivalent ion compositions were determined for different spinel minerals, leading to enhanced radiation shielding efficiency. The findings offer valuable perspectives for refining and optimization of spinel materials for use in radiation applications.

Two-dimensional few-atom noble gas clusters in a graphene sandwich.

The van der Waals atomic solids of noble gases on metals at cryogenic temperatures were the first experimental examples of two-dimensional systems. Recently, such structures have also been created on surfaces under encapsulation by graphene, allowing studies at elevated temperatures through scanning tunnelling microscopy. However, for this technique, the encapsulation layer often obscures the arrangement of the noble gas atoms. Here we create Kr and Xe clusters in between two suspended graphene layers, and uncover their atomic structure through transmission electron microscopy. We show that small crystals (N < 9) arrange on the basis of the simple non-directional van der Waals interaction. Larger crystals show some deviations, possibly enabled by deformations in the encapsulating graphene lattice. We further discuss the dynamics of the clusters within the graphene sandwich, and show that although all the Xe clusters with up to N ≈ 100 remain solid, Kr clusters with already N ≈ 16 turn occasionally fluid under our experimental conditions (under a pressure of ~0.3 GPa). This study opens a way for the so-far unexplored frontier of encapsulated two-dimensional van der Waals solids with exciting possibilities for fundamental condensed-matter physics research and possible applications in quantum information technology.

Development and strategy of alumina-mullite diphasic fibers with high thermal stability

Controlling coordinately heterogeneous grain growth is challenging for preparing multiphase structural materials, especially for high-performance alumina-based fibers. In this study, we achieved refining the mullite grains by controlling the composition of the silicon source, resulting in the successful preparation of fine-grained alumina-mullite diphasic fibers with high thermal stability. The alumina-mullite diphasic fibers consisted of lamellar α-Al2O3 and mosaic-like mullite grains with a biphasic grain size below 500 nm. The Weibull strength of diphasic fibers could reach 1.70 GPa. The strength retention rate exceeded 85% even after thermal exposure at 1100 ℃ for 50 h and at 1200 ℃ for 5 h. Moreover, our investigation revealed the presence of an ordered complexion on the (0001) plane of α-Al2O3 and discussed a possible situation of its two-dimensional atomic arrangement distribution, providing great enlightenment for understanding grain boundary segregation theory.

Nano‐bio interactions between 2D nanomaterials and mononuclear phagocyte system cells

AbstractTwo‐dimensional (2D) nanomaterials, known for their unique atomic arrangements and exceptional physicochemical properties, have garnered significant attention in biomedical applications, particularly in the realms of immunotherapy for tissue engineering and tumor therapy. These applications necessitate a thorough assessment of the potential influence of 2D nanomaterials on immune cells. Notably, the mononuclear phagocyte system (MPS) cells, which play pivotal roles in both innate and adaptive immunity, are essential for maintaining organismal homeostasis. MPS cells with phagocytic capability contribute to the prevention of foreign body invasion and the elimination of dead or senescent cells. Furthermore, MPS cells, including macrophages and dendritic cells, serve as vital bridges between innate and adaptive immune responses. Therefore, understanding the nano‐bio interactions between 2D nanomaterials and MPS cells is imperative. These nano‐bio interactions including cellular uptake, cytocompatibility, and immunological impact are invaluable for the purposeful design of 2D nanomaterials. Herein, we provide an overview of the latest advancements in understanding the nano‐bio interactions between 2D nanomaterials and MPS cells, and discuss the current challenges and future prospects of employing 2D nanomaterials in the field of nanomedicine.

Off‐Centering of Ge Atoms in GeBi2Te4 and Impact on Thermoelectric Performance

AbstractThe crystal structure and transport properties of GeBi2Te4 are investigated as a layered compound with potential applications as thermoelectric materials. A disordered arrangement of Ge and Bi atoms in a septuple‐layer structure is discovered through synchrotron radiation X‐ray diffraction and transmission electron microscopy. Neutron pair distribution function analysis revealed the presence of discordant Ge atoms with an off‐centering distance of 0.12 Å at 300 K. The thermal conductivity of GeBi2Te4 is very low due to the strong phonon scattering. This is a result of the three Einstein local oscillators coupled with the disordered arrangement of atoms. This study also explores further the structural characteristics of these materials and their associated phonon scattering processes. The effect of Sb substitution for Ge on the electrical transport properties of the sample is profound, resulting in a change from p‐type to n‐type conduction. An enhanced thermoelectric figure of merit (ZT) of 0.45 at 523 K in the in‐plane direction is obtained. This research provides valuable insights into the crystal structure and transport properties of GeBi2Te4, showcasing its promising role as a thermoelectric material with potential for near‐room‐temperature applications.

Structure and electrical properties of double-walled silicon nanotubes depending on 585 defects and applied electric fields by SCC-DFTB method

The geometric structural and electronic properties of 585 defective double-walled silicon nanotubes (DWSiNTs) by using the self-consistent charge density functional tight-binding (SCC-DFTB) method. Furthermore, we investigated the impact of external electric field and intensity on the electronic properties. After the relaxation of perfect tubes, the structure of the tube changes significantly, and the winding direction of the tube wall changes. The buckling value of the tube wall is most closely related to the geometric shape and atomic arrangement order of tubes. The overall stability of zigzag tubes is higher than armchair tubes, and (6,6)@(10,10) stability is significantly affected by defects. The partially defected zigzag tubes change from direct band gap semiconductor properties to indirect band gap semi-metal properties. A transformation of the semiconductor-semimetal properties, direct-indirect band gap of DWSiNTs is realized. The charge transfer amplitude of the defect tubes is greater than the perfect tube. The applied electric field makes the stability of all tubes decrease linearly, and the stability of the defect tubes is higher than the perfect tube. Part of the electric field strength changes the defect tubes from semiconductor properties to semi-metal properties, and semi-metal properties to metal properties. These theoretical studies provide a reference for the preparation and future application of DWSiNTs.

Planar defects and strain distributions in polycrystalline BaFe2As2 superconductors synthesized by mechanochemical methods

In this study, the microstructure of polycrystalline Co-doped BaFe2As2 superconducting bulks was comprehensively analyzed. The synthesis process involved ball milling and subsequent spark plasma sintering (SPS). A strong correlation between the microstructure and synthesis conditions was observed. Specifically, when mechanochemical synthesis of raw metal powders was carried out at a ball milling energy (EBM) of 100 MJ/kg, the resulting Co-BaFe2As2 bulk contained nanograins with a high density of planar defects and exhibited a high critical current density (Jc) under both magnetic and self-fields. The findings suggest that planar defects are one of the influential factors on the superconducting properties. Atomic-resolution microstructural characterization revealed that the planar defects are parallel to (001) and exhibit distinctive atomic arrangements. Atomic-resolution elemental mappings displayed a remarkable barium concentration in planar defects and grain boundaries compared to the BaFe2As2 matrix. Local strain fields were also observed around planar defects, especially near their edges. These nanoscale strain fields could be considered as volumetric pinning centers, and effectively pin flux vortices in the random crystal orientation, thereby increasing Jc in the Fe-based superconducting bulk. Additionally, an extended investigation was performed to include a K-doped BaFe2As2 bulk that exhibits similar planar defects. Based on the results of the microstructural analysis, speculations were mode on the evolution process of the microstructure during the preparation of BaFe2As2 bulks.

Identification of Kikuchi lines in electron diffraction patterns collected in small-angle geometry.

It is demonstrated that Kikuchi features become clearly visible if reflection high-energy electron diffraction (RHEED) patterns are filtered using digital image processing software. The results of such pattern transformations are shown for SrTiO3 with mixed surface termination for data collected at different azimuths of the incident electron beam. A simplified analytical approach for the theoretical description of filtered Kikuchi patterns is proposed and discussed. Some examples of raw and filtered patterns for thin films are shown. RHEED patterns may be treated as a result of coherent and incoherent scattering of electron waves. The effects of coherent scattering may be considered as those occurring due to wave diffraction by an idealized crystal and, usually, only effects of this type are analysed to obtain structural information on samples investigated with the use of RHEED. However, some incoherent scattering effects mostly caused by thermal vibrations of atoms, known as Kikuchi effects, may also be a source of valuable information on the arrangements of atoms near the surface. Typically, for the case of RHEED, Kikuchi features are hidden in the intensity background and researchers cannot easily recognize them. In this paper, it is shown that the visibility of features of this type can be substantially enhanced using computer graphics methods.

Covalent organic framework isomers with divergent photocatalytic properties.

A pair of isomeric Py-BT-COFs with the same composition, but slightly different atomic arrangements, were designed and synthesized. The minute structural variations of the Py-BT-COF isomers generated significantly different redox and photophysical properties and correspondingly led to different photocatalytic manifestations in H2 evolution and rhodamine B degradation.

High entropy alloys and methods for synthesis

High entropy alloys (HEA) are now a well-known group of materials, which has been studied intensely in the past decade. Due to the high complexity of the various HEA structures and the wide compositional spectrum, the research in the field continues with important discoveries and high work volume. Numerous articles presented various modalities to describe the thermodynamics and atomic arrangement in HEA structures and develop specific criteria for the selection of compositions with predicted solid solution structures. The next step towards the industrial use of the new category of alloys needs to be taken and implies the necessity to describe the implications of methods for alloy synthesis, as the structures obtained would be the closest to the theoretically assumed equilibrium. A succinct review of the methods and results were presented in the article.

Intermetallics with sp-d orbital hybridisation: morphologies, stabilities and work functions of In-Pd particles at the nanoscale.

The field of intermetallic catalysts, alloying a p-block and a transition metal to form a pM-TM bimetallic alloy, is experiencing robust growth, emerging as a vibrant frontier in catalysis research. Although such materials are increasingly used in the form of nanoparticles, a precise description of their atomic arrangements at the nanoscale remains scarce. Based on the In-Pd binary as a typical pM-TM system, we performed density functional theory calculations to investigate the morphologies, relative stabilities and electronic properties of 24 Å and 36 Å nanoparticles built from the In3Pd2, InPd and InPd3 compounds. Wulff equilibrium structures are compared to other ordered and disordered structures. Surface energies are computed to discuss their thermodynamic stability, while work functions are calculated to examine their electronic structures. For any compound, increasing the size leads to the stabilisation of Wulff polyhedra, which are found to offer smaller surface energies than non-crystalline and chemically disordered structures. Disordered In3Pd2 and InPd nanoparticles show a tendency towards amorphisation, owing to repulsive short In-In bonds. Tuning nanoparticles' work functions can be achieved through the control of the surface structure and composition, by virtue of the roughly linear correlation found between the surface composition and the work function which nevertheless includes a certain number of outliers. This work paves the way to rationalisation of both structural and electronic properties of pM-TM nanoparticles.

Crystal structures, bonding and electronic structures of α- and β-Ir2B3-x compounds.

The binary boron-rich compounds α-Ir2B3-x and β-Ir2B3-x, formerly denoted as α- and β-Ir4B5, were synthesized via both arc melting followed by annealing at 800 °C (900 °C) and high-temperature thermal treatment of mixtures of the elements. X-ray structure analysis of α-Ir2B3-x was performed on a single crystal (space group C2/m, a = 10.5515(11) Å, b = 2.8842(3) Å, c = 6.0965(7) Å, β = 91.121(9)°). The orthorhombic structure of β-Ir2B3-x was confirmed by X-ray powder diffraction (space group Pnma; a = 10.7519(3) Å, b = 2.83193(7) Å, c = 6.0293(1) Å). The α-Ir2B3-x structure exhibits ordered arrangements of iridium atoms. The structure is composed of corrugated layers of boron hexagons (interlinked via external B-B bonds) alternating with two corrugated layers of iridium along the c-direction; an additional boron atom (Oc. 0.46(7)) is located between iridium layers in Ir6 trigonal prisms. The boron partial structure in β-Ir2B3-x is composed of ribbons made up of slightly corrugated quadrilateral units running along the b-direction in the channels formed by 8 iridium atoms each. DFT calculations revealed a number of bands crossing the Fermi level, predicting metallic behaviors of the two compounds. β-Ir2B3-x is characterized by a pseudogap around the Fermi level and a smaller eDOS of 0.6405 states per eV per f.u. at the Fermi level, as compared to the α-Ir2B3-x value of 1.405 states per eV per f.u. The calculated electron localization functions revealed strong covalent bonds between boron atoms in the core part of the B6 hexagons, metallic B-B bonds within the quadrilateral boron partial structure and mixed covalent and metallic interactions between iridium and boron atoms. Structural relationships of α-Ir2B3-x and β-Ir2B3-x with ReB2-type structures as well as the common structural features with layered binary borides with CrB-type related structures have been discussed.

Enhancing Predictions of Drug Solubility through Multidimensional Structural Characterization Exploitation.

Solubility is not only a significant physical property of molecules but also a vital factor in smallmolecule drug development. Determining drug solubility demands stringent equipment, controlled environments, and substantial human and material resources. The accurate prediction of drug solubility using computational methods has long been a goal for researchers. In this study, we introduce MSCSol, a solubility prediction model that integrates multidimensional molecular structure information. We incorporate a graph neural network with geometric vector perceptrons (GVP-GNN) to encode 3D molecular structures, representing spatial arrangement and orientation of atoms, as well as atomic sequences and interactions. We also employ Selective Kernel Convolution combined with Global and Local attention mechanisms to capture molecular features context at different scales. Additionally, various descriptors are calculated to enrich the molecular representation. For the 2D and 3D structural data of molecules, we design different data augmentation strategies to enhance generalization ability and prevent the model from learning irrelevant information. Extensive experiments on benchmark and independent datasets demonstrate MSCSol's superior performance. Ablation studies further confirm the effectiveness of different modules. Interpretability analysis highlights the importance of various atomic groups and substructures for solubility and verifies that our model effectively captures functional molecular structures and higher-order knowledge. The source code and datasets are freely available at https://github.com/ZiyuFanCSU/MSCSol.

On surface synthesis of an eleven-ring sulfur-doped nonacene.

Dithienoacenes with a heptacene core, heptaceno[2,3-b:11,12-b']bis[1]benzothiophene, have been synthesized through the combination of solution and surface assisted chemistry. The atomic composition, structural arrangement and electronic properties of the molecules on the Au(111) surface have been deeply explored by non-contact atomic force microscopy (nc-AFM), bond-resolved scanning tunnelling microscopy (BR-STM) and scanning tunneling spectroscopy (STS) corroborated by density functional theory (DFT) calculations. Our combined experiments reveal modifications induced by sulfur substitution.

Atomic structure and water arrangement on K-feldspar microcline (001).

The properties of clouds, such as their reflectivity or their likelihood to precipitate, depend on whether the cloud droplets are liquid or frozen. Thus, understanding the ice nucleation mechanisms is essential for the development of reliable climate models. Most ice nucleation in the atmosphere is heterogeneous, i.e., caused by ice nucleating particles such as mineral dusts or organic aerosols. In this regard, K-feldspar minerals have attracted great interest recently as they have been identified as one of the most important ice nucleating particles under mixed-phase cloud conditions. The mechanism by which feldspar minerals facilitate ice nucleation remains, however, elusive. Here, we present atomic force microscopy (AFM) experiments on microcline (001) performed in an ultrahigh vacuum and at the solid-water interface together with density functional theory (DFT) and molecular dynamics (MD) calculations. Our ultrahigh vacuum data reveal features consistent with a hydroxyl-terminated surface. This finding suggests that water in the residual gas readily reacts with the surface. Indeed, the corresponding DFT calculations confirm a dissociative water adsorption. Three-dimensional AFM measurements performed at the mineral-water interface unravel a layered hydration structure with two features per surface unit cell. A comparison with MD calculations suggests that the structure observed in AFM corresponds to the second hydration layer rather than the first water layer. In agreement with previous computation results, no ice-like structure is seen, questioning an explanation of the ice nucleation ability by lattice match. Our results provide an atomic-scale benchmark for the clean and water-covered microcline (001) plane, which is mandatory for understanding the ice nucleation mechanism on feldspar minerals.

Spiers Memorial Lecture: NMR crystallography.

Chemical function is directly related to the spatial arrangement of atoms. Consequently, the determination of atomic-level three-dimensional structures has transformed molecular and materials science over the past 60 years. In this context, solid-state NMR has emerged to become the method of choice for atomic-level characterization of complex materials in powder form. In the following we present an overview of current methods for chemical shift driven NMR crystallography, illustrated with applications to complex materials.

%VBur index and steric maps: from predictive catalysis to machine learning.

Steric indices are parameters used in chemistry to describe the spatial arrangement of atoms or groups of atoms in molecules. They are important in determining the reactivity, stability, and physical properties of chemical compounds. One commonly used steric index is the steric hindrance, which refers to the obstruction or hindrance of movement in a molecule caused by bulky substituents or functional groups. Steric hindrance can affect the reactivity of a molecule by altering the accessibility of its reactive sites and influencing the geometry of its transition states. Notably, the Tolman cone angle and %VBur are prominent among these indices. Actually, steric effects can also be described using the concept of steric bulk, which refers to the space occupied by a molecule or functional group. Steric bulk can affect the solubility, melting point, boiling point, and viscosity of a substance. Even though electronic indices are more widely used, they have certain drawbacks that might shift preferences towards others. They present a higher computational cost, and often, the weight of electronics in correlation with chemical properties, e.g. binding energies, falls short in comparison to %VBur. However, it is worth noting that this may be because the steric index inherently captures part of the electronic content. Overall, steric indices play an important role in understanding the behaviour of chemical compounds and can be used to predict their reactivity, stability, and physical properties. Predictive chemistry is an approach to chemical research that uses computational methods to anticipate the properties and behaviour of these compounds and reactions, facilitating the design of new compounds and reactivities. Within this domain, predictive catalysis specifically targets the prediction of the performance and behaviour of catalysts. Ultimately, the goal is to identify new catalysts with optimal properties, leading to chemical processes that are both more efficient and sustainable. In this framework, %VBur can be a key metric for deepening our understanding of catalysis, emphasizing predictive catalysis and sustainability. Those latter concepts are needed to direct our efforts toward identifying the optimal catalyst for any reaction, minimizing waste, and reducing experimental efforts while maximizing the efficacy of the computational methods.