Crystal-like Order Research Articles

Advanced properties of gold nanoparticles obtained by using long-chain secondary amine for phase transfer from water to chloroform

We have conducted a new comparison of gold nanoparticles functionalized by primary- and secondary amine with the same chain length. Our hypothesis suggests that the adaptive steric conformation of the secondary amine molecular branches makes a marked additional contribution to the well-established role of the ligand chain length. We characterize the importance of this factor based on diOctadecylamine (diODA) and Octadecylamine (ODA) passivated gold nanoparticles by using high-resolution transmission electron microscopy (HR-TEM) and selective area electron diffraction (SAED). The results evidenced that the diODA coordination to the inorganic core forms a more efficient and impenetrable protective coating. The SAED patterns show a more homogeneous distribution of the small crystalline domains in the gold core. TEM images show a smooth spherical shape of the diODA nanoparticles and a lack of interparticle coalescence cases. The diODA-passivation provides nanoparticles with nearly twice the effective ligand length than its ODA equivalent. This results in their spontaneous arrangement in domains with expressed crystal-like order despite the relatively large size-dispersity before passivation. The surface free energy of coatings, formed by diODA passivated gold nanoparticles, is twice as small as measured on the ODA-nanoparticle-coated surfaces.

Microstructural stability and mechanical property of AlCrFeMoTi high-entropy amorphous alloy thin films under He+ ions irradiation

High-entropy amorphous materials have recently proved exceptional radiation resistance, showing potential as a candidate materials for nuclear industry applications. This study synthesized nearly equi-atomic AlCrFeMoTi high-entropy amorphous thin films with a thickness of about 499 nm using magnetron sputtering. The prepared films were subjected to low dose, 0.5 MeV He+ ion irradiation, with varying irradiation damage ranging from 0.01 to 0.1 displacement per atom (dpa). Increasing the irradiation dose led to a decrease in the radius of the inner diffraction halo (r) and an increase in the crystal-like order, indicating an irradiation-induced structural relaxation process within the amorphous matrix. This relaxation results in more efficient atomic packing, yielding a denser amorphous structure and enhanced hardness of AlCrFeMoTi high-entropy amorphous thin films. This study demonstrates that AlCrFeMoTi high-entropy amorphous thin films exhibit remarkable radiation resistance, with stable microstructure and mechanical properties under He+ irradiation, making them promising candidates for applications in the nuclear industry.

The new Iridium-Hafnium-Aluminum alloy thin films with excellent mechanical properties and oxidation resistance

Improving oxidation resistance has long been a challenge for hot end components in high temperature environments. We have fabricated a series of IraHfbAlc (at. %) alloy thin films by multi-targeted direct current magnetron sputtering (DC-MS) and have thoroughly investigated the microscopic mechanism of the films. More importantly, we for the first time prepared IraHfbAlc alloy thin films with a preferred (111) orientation substitution solid solution, which exhibits excellent mechanical properties and oxidation resistance. The minimum surface roughness (Ra) value of the IraHfbAlc alloy films was 0.7 nm, while the maximum hardness (H) and elastic modulus (E) exceeded 20 GPa and 330 GPa, respectively. The oxidized volatility of the Ir in the films was only 0.11 μm/h at 1300 °C (lower than most previously reported values, such as 0.5 μm/h), which greatly improved the lifetime of the film. Confirmation that lattice distortion induces the refinement of crystal-like order (CLO) in thin films, and solves the mystery of enhanced oxidation resistance. The findings provide important insights into the design of Ir-containing alloy coatings and offer new ideas in the field of high-temperature protection.

Toughening oxide glasses through paracrystallization.

Glasses, unlike crystals, are intrinsically brittle due to the absence of microstructure-controlled toughening, creating fundamental constraints for their technological applications. Consequently, strategies for toughening glasses without compromising their other advantageous properties have been long sought after but elusive. Here we report exceptional toughening in oxide glasses via paracrystallization, using aluminosilicate glass as an example. By combining experiments and computational modelling, we demonstrate the uniform formation of crystal-like medium-range order clusters pervading the glass structure as a result of paracrystallization under high-pressure and high-temperature conditions. The paracrystalline oxide glasses display superior toughness, reaching up to 1.99 ± 0.06 MPa m1/2, surpassing any other reported bulk oxide glasses, to the best of our knowledge. We attribute this exceptional toughening to the excitation of multiple shear bands caused by a stress-induced inverse transformation from the paracrystalline to amorphous states, revealing plastic deformation characteristics. This discovery presents a potent strategy for designing highly damage-tolerant glass materials and emphasizes the substantial influence of atomic-level structural variation on the properties of oxide glasses.

Emergence of tunable periodic density correlations in a Floquet–Bloch system

In quantum gases, two-body interactions are responsible for a variety of instabilities that depend on the characteristics of both trapping and interactions. These instabilities can lead to the appearance of new structures or patterns. We report on the Floquet engineering of such a parametric instability, on a Bose-Einstein condensate held in a time-modulated optical lattice. The modulation triggers a destabilization of the condensate into a state exhibiting a density modulation with a new spatial periodicity. This new crystal-like order, which shares characteristic correlation properties with a supersolid, directly depends on the modulation parameters: The interplay between the Floquet spectrum and interactions generates narrow and adjustable instability regions, leading to the growth, from quantum or thermal fluctuations, of modes with a density modulation noncommensurate with the lattice spacing. This study demonstrates the production of metastable exotic states of matter through Floquet engineering and paves the way for further studies of dissipation in the resulting phase and of similar phenomena in other geometries.

Influence of structural heterogeneity on shear bands in fracture-affected zones of metallic glasses

The catastrophic fracture of metallic glasses (MGs) caused by shear banding limits its engineering application. Structural heterogeneity of MGs strongly affects the shear banding process during plastic deformation. Here, we study the microstructure of MG fibers of different Poisson's ratios or structural heterogeneities after stretching them to fracture using synchrotron X-ray nano-computed tomography with the combination of high-resolution transmission electron microscopy. It is found that interlaminated high- and low-density layers induced by shear banding appear in the fracture-affected zone of the MG fibers. Meanwhile, the fraction of crystal-like order regions in the fracture-affected zone is larger than that of the unaffected matrix. With the increase of Poisson's ratio, the number of low-density shear bands (SBs) increases, and the thickness of a single high-density layer around SBs decreases in fracture-affected zone. The size of fracture-affected zone increases from ∼310 nm for La60Ni15Al25 MG to ∼920 nm for Pd40Cu30Ni10P20 MG. The results help to understand the influence of structural heterogeneity on the plastic deformation of MGs.

Revealing the role of liquid preordering in crystallisation of supercooled liquids

The recent discovery of non-classical crystal nucleation pathways has revealed the role of fluctuations in the liquid structural order, not considered in classical nucleation theory. On the other hand, classical crystal growth theory states that crystal growth is independent of interfacial energy, but this is questionable. Here we elucidate the role of liquid structural ordering in crystal nucleation and growth using computer simulations of supercooled liquids. We find that suppressing the crystal-like structural order in the supercooled liquid through a new order-killing strategy can reduce the crystallisation rate by several orders of magnitude. This indicates that crystal-like liquid preordering and the associated interfacial energy reduction play an essential role in nucleation and growth processes, forcing critical modifications of the classical crystal growth theory. Furthermore, we evaluate the importance of this additional factor for different types of liquids. These findings shed new light on the fundamental understanding of crystal growth kinetics.

Evolution of local densities during shear banding in Zr-based metallic glass micropillars

Shear bands (SBs) play an important role in plastic deformation of metallic glasses (MGs), but the evolving mechanism of SBs is still elusive. We study the structural formation and evolution of SBs inside MGs using synchrotron X-ray nano-computed tomography with the combination of high-resolution transmission electron microscopy. It is found that discrete anisotropic low-density regions, as manifestation of the activations of accumulated shear transformation zones, are created in the elastic deformation regime, which form SBs of density fluctuations under large plastic deformation. With further increasing plastic strain, the thickness of SBs increases from ∼ 105 nm to ∼ 180 nm, and their local densities decrease. Before the formation of cracks, the low-density regions in SBs gradually evolve into nanovoids with the matrix around densified. Compared to the unaffected matrix, densified regions with more crystal-like order (CLO) structure appear around thick SBs of severe bond breaking, and the densification is more apparent near crack surface with CLO structure further increasing. The results are significant for understanding the structural evolution during shear banding and plastic deformation mechanism for glassy materials.

Nanoengineering of Curved Supramolecular Polymers: Toward Single-Chain Mesoscale Materials

ConspectusRecently, supramolecular polymers (SPs), which depend on the formation of reversible bonds between monomers, have attracted attention as a class of materials that can overcome the potential environmental problems of conventional polymeric materials. The development of various supramolecular polymers is important not only for their direct application as materials but also because their unique polymerization processes and dynamic properties have a profound influence on the development of polymeric and small-molecule-based functional materials. In other words, by limiting the dimensionality of molecular assemblies to one dimension, we can discover the essential aspects of self-assembly and self-organization. In particular, supramolecular polymerization, in which π-electron-rich planar molecules are stacked one-dimensionally via multiple interactions, is interesting because it gives “π-stacked SPs” with one-dimensional crystal-like order. The excellent intrinsic (internal) structural order of π-stacked SPs is difficult to observe in higher-order structures that exhibit only a monotonous linear structure. However, our research has shown that when internal structural order intrinsically generates curvature, the curvature appears as a major feature of the entire polymer chain. This intrinsic curvature allows the formation of diverse topologies such as toroids, random coils, waves, spirals, and helicoids using π-stacked SPs and also allows structural changes at the single-polymer-chain level along a topology-dependent energy landscape. In other words, π-stacked SP-based nanomaterials could enable free control of the structure at the single-polymer-chain level. This Account will focus on our research into curved supramolecular polymers (CSPs) during the last five years. CSPs are formed by the hydrogen bonding between barbiturate-containing π-conjugated molecules to produce giant supramolecular monomers. We first give an overview of the molecular design of the monomers required for the formation of CSPs, the unique energy landscape of CSPs, and their evaluation and analysis methods, before describing the four specific properties of CSPs. The first is structural controllability via the introduction of photoresponsive units such as azobenzene and diarylethene moieties. The isomerization of these photochromic molecules within the CSP main chain has a local effect on the curvature and allows photocontrol of their entire topology. The second is the copolymerization of different molecules via the formation of rosettes. Here, two extreme examples, block and alternating copolymerization, are discussed. Third, we describe a structural transition that involves the rearrangement of hydrogen bonds. This is a new property, which enables a structural transition from a soft and highly soluble supramolecular polymer to a hard and poorly soluble crystalline structure and thus expands the applicability of CSPs to environmentally important and electronic materials. Finally, self-assembled polycatenanes are described as an example of an entirely new “topological self-organization” using CSP formation on CSP surfaces, i.e., secondary nucleation. This work is also a turning point in our CSP research and includes concepts that are broadly applicable to the creation of self-organized functional materials. At the end of this Account, we will discuss how CSPs can contribute to nanotechnology or mesotechnology as single-chain-polymer materials. We hope that the landscape depicted in this Account will guide the development of a variety of new functional materials.

Ordering in liquid and its heredity impact on phase transformation of Mg-Al-Ca alloys

It is a long-sought goal to achieve desired mechanical properties through tailoring phase formation in alloys, especially for complicated multi-phase alloys. In fact, unveiling nucleation of competitive crystalline phases during solidification hinges on the nature of liquid. Here we employ ab initio molecular dynamics simulations (AIMD) to reveal liquid configuration of the Mg-Al-Ca alloys and explore its effect on the transformation of Ca-containing Laves phase from Al2Ca to Mg2Ca with increasing Ca/Al ratio (rCa/Al). There is structural similarity between liquid and crystalline phase in terms of the local arrangement environment, and the connection schemes of polyhedras. The forming signature of Mg2Ca, as hinted by the topological and chemical short-range order originating from liquid, ascends monotonically with increasing rCa/Al. However, Al2Ca crystal-like order increase at first and then decrease at the crossover of rCa/Al = 0.74, corresponding to experimental composition of phase transition from Al2Ca to Mg2Ca. The origin of phase transformation across different compositions lies in the dense packing of atomic configurations and preferential bonding of chemical species in both liquid and solid. The present finding provides a feasible scenario for manipulating phase formation to achieve high performance alloys by tailoring the crystal-like order in liquid.

Nucleation and Post-Nucleation Growth in Diffusion-Controlled and Hydrodynamic Theory of Solidification

Two-step nucleation and subsequent growth processes were investigated in the framework of the single mode phase-field crystal model combined with diffusive dynamics (corresponding to colloid suspensions) and hydrodynamical density relaxation (simple liquids). It is found that independently of dynamics, nucleation starts with the formation of solid precursor clusters that consist of domains with noncrystalline ordering (ringlike projections are seen from certain angles), and regions that have amorphous structure. Using the average bond order parameter q¯6, we distinguished amorphous, medium range crystallike order (MRCO), and crystalline local orders. We show that crystallization to the stable body-centered cubic phase is preceded by the formation of a mixture of amorphous and MRCO structures. We have determined the time dependence of the phase composition of the forming solid state. We also investigated the time/size dependence of the growth rate for solidification. The bond order analysis indicates similar structural transitions during solidification in the case of diffusive and hydrodynamic density relaxation.

Using Deposition Rate and Substrate Temperature to Manipulate Liquid Crystal-Like Order in a Vapor-Deposited Hexagonal Columnar Glass.

We investigate vapor-deposited glasses of a phenanthroperylene ester, known to form an equilibrium hexagonal columnar phase, and show that liquid crystal-like order can be manipulated by the choice of deposition rate and substrate temperature during deposition. We find that rate-temperature superposition (RTS)-the equivalence of lowering the deposition rate and increasing the substrate temperature-can be used to predict and control the molecular orientation in vapor-deposited glasses over a wide range of substrate temperatures (0.75-1.0 Tg). This work extends RTS to a new structural motif, hexagonal columnar liquid crystal order, which is being explored for organic electronic applications. By several metrics, including the apparent average face-to-face nearest-neighbor distance, physical vapor deposition (PVD) glasses of the phenanthroperylene ester are as ordered as the glass prepared by cooling the equilibrium liquid crystal. By other measures, the PVD glasses are less ordered than the cooled liquid crystal. We explain the difference in the maximum attainable order with the existence of a gradient in molecular mobility at the free surface of a liquid crystal and its impact upon different mechanisms of structural rearrangement. This free surface equilibration mechanism explains the success of the RTS principle and provides guidance regarding the types of order most readily enhanced by vapor deposition. This work extends the applicability of RTS to include molecular systems with a diverse range of higher-order liquid-crystalline morphologies that could be useful for new organic electronic applications.

Minimal statistical-mechanical model for multihyperuniform patterns in avian retina

Birds are known for their extremely acute sense of vision. The very peculiar structural distribution of five different types of cones in the retina underlies this exquisite ability to sample light. It was recently found that each cone population as well as their total population display a disordered pattern in which long-wavelength density fluctuations vanish [Jiao etal., Phys. Rev. E 89, 022721 (2014)PLEEE81539-375510.1103/PhysRevE.89.022721]. This property, known as hyperuniformity, is also present in perfect crystals. In situations like the avian retina in which both the global structure and that of each component display hyperuniformity, the system is said to be multihyperuniform. In this work, we aim at devising a minimal statistical-mechanical model that can reproduce the main features of the spatial distribution of photoreceptors in avian retina, namely the presence of disorder, multihyperuniformity, and local heterocoordination. This last feature is key to avoiding local clustering of the same type of photoreceptors, an undesirable feature for the efficient sampling of light. For this purpose, we formulate a minimal statistical-mechanical model that definitively exhibits the required structural properties: an equimolar three-component mixture (one component to sample each primary color: red, green, and blue) of nonadditive hard disks to which a long-range logarithmic repulsion is added between like particles. Interestingly, a Voronoi analysis of our idealized system of photoreceptors shows that the space-filling Voronoi polygons display a rather uniform area distribution, symmetrically centered around that of a regular lattice, a structural property also found in human retina. Disordered multihyperuniformity offers an alternative to generate photoreceptor patterns with minimal long-range concentration and density fluctuations. This is the key to overcoming the difficulties in devising an efficient visual system in which crystal-like order is absent.

Crystal-like order and defects in metazoan epithelia with spherical geometry

Since Robert Hooke studied cork cell patterns in 1665, scientists have been puzzled by why cells form such ordered structures. The laws underlying this type of organization are universal, and we study them comparing the living and non-living two-dimensional systems self-organizing at the spherical surface. Such-type physical systems often possess trigonal order with specific elongated defects, scars and pleats, where the 5-valence and 7-valence vertices alternate. In spite of the fact that the same physical and topological rules are involved in the structural organization of biological systems, such topological defects were never reported in epithelia. We have discovered them in the follicular spherical epithelium of ascidians that are emerging models in developmental biology. Surprisingly, the considered defects appear in the epithelium even when the number of cells in it is significantly less than the previously known threshold value. We explain this result by differences in the cell sizes and check our hypothesis considering the self-assembly of different random size particles on the spherical surface. Scars, pleats and other complex defects found in ascidian samples can play an unexpected and decisive role in the permanent renewal and reorganization of epithelia, which forms or lines many tissues and organs in metazoans.

Ductile Co-based bulk metallic glass with superhigh strength and excellent soft magnetic properties induced by modulation of structural heterogeneity

The development of Co-based bulk metallic glasses (BMGs) with satisfying comprehensive properties, including large glass-forming ability, high strength, large plasticity and excellent soft magnetic properties, is in high need for applications as structural and functional materials. A (Co0.7Fe0.2Ni0.1)67.7B21.9Si5.1Nb5Cu0.3 BMG with a record large plasticity of 5.5%, a high fracture strength of 4770 MPa, and a large critical diameter of 3.5 mm is successfully developed. This BMG also shows good soft magnetic properties, i.e. low coercivity (Hc) of 1.33 A/m and higher saturation magnetization (Bs) of 0.60 T. The enhanced strength and plasticity, as well as high Bs of this BMG, are all attributed to the minor addition of Cu in (Co0.7Fe0.2Ni0.1)68-xB21.9Si5.1Nb5Cux (x = 0, 0.1, 0.3, 0.5 and 0.7 at.%) system. The reduced average atomic spacing in the BMG, which comes from the squeezed spacing between Co, Fe, Ni and Nb atoms with proper addition of Cu, results in the improvement of fracture strength and Bs. The atomic-scale structural heterogeneity with the formation of crystal-like order structures is induced in the amorphous matrix, and thus the plasticity of (Co0.7Fe0.2Ni0.1)67.7B21.9Si5.1Nb5Cu0.3 BMG increases in spite of the decreased average atomic spacing.

Vapor deposition of a nonmesogen prepares highly structured organic glasses

We show that glasses with aligned smectic liquid crystal-like order can be produced by physical vapor deposition of a molecule without any equilibrium liquid crystal phases. Smectic-like order in vapor-deposited films was characterized by wide-angle X-ray scattering. A surface equilibration mechanism predicts the highly smectic-like vapor-deposited structure to be a result of significant vertical anchoring at the surface of the equilibrium liquid, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy orientation analysis confirms this prediction. Understanding of the mechanism enables informed engineering of different levels of smectic order in vapor-deposited glasses to suit various applications. The preparation of a glass with orientational and translational order from a nonliquid crystal opens up an exciting paradigm for accessing extreme anisotropy in glassy solids.

Vitrification, crystallization, and atomic structure of deformed and quenched Ni60Nb40 metallic glass

A Ni60Nb40 alloy was vitrified from fcc Ni and bcc Nb by cold rolling and by rapid solidification of an alloy ingot. The Ni60Nb40 that was vitrified by rolling has a lower crystallization onset temperature with single crystallization reaction compared to the two-stage crystallization at higher temperature for quenched Ni60Nb40. Fluctuation electron microscopy and hybrid reverse Monte Carlo modeling show that the as-rolled Ni60Nb40 contains fewer icosahedral-like Voronoi clusters and more crystal-like and bcc-like Voronoi clusters, which are inherited from the bcc Nb. The crystal-like and bcc-like medium range order clusters may be the structural origin for lower crystallization temperature in the as-rolled glass. It is demonstrated that hybrid reverse Monte Carlo simulations incorporating fluctuation microscopy and an empirical interatomic potential are insensitive to the starting structure.

Correlation between Local Structure Order and Spatial Heterogeneity in a Metallic Glass.

Although nanoscale spatial heterogeneity of metallic glasses has been demonstrated by extensive experimental and theoretical investigations, the nature of spatial heterogeneity remains poorly known owing to the absence of a structural depiction of the inhomogeneity from experimental insight. Here we report the experimental characterization of the spatial heterogeneity of a metallic glass by utilizing state-of-the-art angstrom-beam electron diffraction and scanning transmission electron microscopy. The subnanoscale electron diffraction reveals that the nanoscale spatial heterogeneity and corresponding density fluctuation have a close correlation with the local structure variation from icosahedronlike to tetragonal crystal-like order. The structural insights of spatial heterogeneity have important implications in understanding the properties and dynamics of metallic glasses.

Confined Polymerization in Highly Ordered Mesoporous Organosilicas.

Hybrid mesoporous organosilica exhibiting crystal-like order in the walls provided an ideal channel reaction vessel for the confined polymerization of acrylonitrile (PAN). The resulting high-molecular-mass PAN fills the channels at high yield and forms an ordered nanostructure of polymer nanobundles enclosed into the hybrid matrix. The in situ thermal transformation of PAN into rigid polyconjugated and, eventually, into condensed polyaromatic carbon nanofibers, retains the periodic architecture. Simultaneously, the matrix evolves showing the fusion of the p-phenylene rings and the cleavage of carbonsilicon bonds: this gives rise to graphitic-carbon/silica nanocomposites containing hyper-oxydrylated silica nanophases. Interestingly, the 3D hexagonal mesostructure survives in the carbonaceous material. The exploitation of porous materials of high capacity and a hybrid nature, for polymerization in the confined state, followed by high temperature treatments, allowed us to achieve unique and precisely fabricated nanostructures, thus paving the way for the construction of fine-tuned electronic and light-harvesting materials.

Anisotropic pair correlations in binary and multicomponent hard-sphere mixtures in the vicinity of a hard wall: A combined density functional theory and simulation study

The fundamental measure approach to classical density functional theory has been shown to be a powerful tool to predict various thermodynamic properties of hard-sphere systems. We employ this approach to determine not only one-particle densities but also two-particle correlations in binary and six-component mixtures of hard spheres in the vicinity of a hard wall. The broken isotropy enables us to carefully test a large variety of theoretically predicted two-particle features by quantitatively comparing them to the results of Brownian dynamics simulations. Specifically, we determine and compare the one-particle density, the total correlation functions, their contact values, and the force distributions acting on a particle. For this purpose, we follow the compressibility route and theoretically calculate the direct correlation functions by taking functional derivatives. We usually observe an excellent agreement between theory and simulations, except for small deviations in cases where local crystal-like order sets in. Our results set the course for further investigations on the consistency of functionals as well as for structural analysis on, e.g., the primitive model. In addition, we demonstrate that due to the suppression of local crystallization, the predictions of six-component mixtures are better than those in bidisperse or monodisperse systems. Finally, we are confident that our results of the structural modulations induced by the wall lead to a deeper understanding of ordering in anisotropic systems in general, the onset of heterogeneous crystallization, caging effects, and glassy dynamics close to a wall, as well as structural properties in systems with confinement.