Long-range Arrangement Research Articles

Structural Basis of Cucurbituril-Containing Self-Assembled Supramolecular Chiral Materials.

Macrocycle-based host-guest complexation offers an intriguing protocol in producing chiroptical materials, while the bulky size and dynamic exchange between hosts and guests hinders the ordered aggregation to afford the long-range chiral arrangement. It remains great challenges in assembling cucurbit[n]urils (CB[n]s) included complexes to induce supramolecular chirality ascribed to the excellent water solubility and flexible packing. Herein, we unveiled the structural basis on the formation of chiroptical coassemblies from CB[n] (n=6, 7) complexes. Perylene diimides (PDIs) with cationic chiral pendants formed complexes in the aqueous media, which selectively showed chiroptical properties. Chlorination at the bay position, increasing alkyl length of cationic chiral pendants or reducing the number of polyaromatic rings would hinder the chiral aggregation. In a comprehensive manner, CB[6] favors ordered aggregation into one-dimensional fibrous nanoarchitectures that greatly facilitates the supramolecular chirality. In contrast, CB[7] with larger cavity and water solubility shrinks the ordered arrangement of complexes, reducing the formation possibility of supramolecular chiral nanoarchitectures. This work suggests the great potential of CB[6] in the preparation and manipulation of supramolecular chiral assemblies, shedding light on the macrocycle-based functional chiroptical materials.

Atomistic-scale insights into hydrogen diffusion barrier in nickel hydride: Complex interplay between short- and long-range hydrogen arrangement and hydrogen concentration

Metal hydrides, such as those containing Pd, Ni and Mg, are being considered as potential candidates for hydrogen storage applications. The sluggish hydrogen uptake/release in such materials at ambient conditions presents a major issue. The timescales are dictated mainly by diffusion, as it is usually the rate-controlling step. In order to identify practical strategies for improving the kinetics, one must therefore gain an atomistic-scale understanding of the hydrogen diffusion, which is generally lacking from experiments. We address this gap by analyzing the hydrogen hopping mechanism and the associated barriers in two million different hydrogen configurations in NiHx (x = 0–1) using computational techniques. A distribution of hopping barriers is observed. The barriers lie between 0.3–0.7 eV. Three factors, namely, the short- and long-range hydrogen arrangement and the hydrogen concentration influence the barrier. We also show that depending on these factors, two different H hopping mechanisms may prevail. At higher H concentration, the lattice expands by as much as 19 % by volume, making it easier for the hydrogen atom to hop. Therefore, hydrogen diffusion is sluggish in the initial α phase, which may explain the experimentally-observed induction behavior. This study highlights the complexity associated with the metal hydride systems and provides the basis for further molecular scale kinetic studies of metal hydride systems.

Stability of ion-beam-induced bixbyite phase in δ-Sc4Hf3O12 under heat treatments and electron beam irradiations

Oxygen-deficient compounds A4B3O12 have a δ-type structure with a regular long-range arrangement of oxygen vacancies induced by compensation of the charge difference between A3+ and B4+ cations, while A and B cations do not order long-range and only display weak short-range correlations. The δ-type compounds in the Sc2O3-HfO2 and Sc2O3-ZrO2 systems exhibit excellent resistance to radiation-induced amorphization, but the long-range ordered δ-phase was transformed into a short-range ordered bixbyite phase. Since this structural change was not predicted from the phase diagram, the validity of the formation of the bixbyite phase and its stability are still unclear. In the present study, the changes of radiation-induced microstructures in δ-Sc4Hf3O12 under heat treatments and electron beam irradiations were examined by ex-situ and in-situ transmission electron microscopy. It was found that the ion-beam-induced metastable bixbyite phase is transformed into the δ and fluorite phases by the rearrangement of the oxygen vacancies.

How Amorphous Nanomaterials Enhanced Electrocatalytic, SERS, and Mechanical Properties.

There is ever-growing research interest in nanomaterials because of the unique properties that emerge on the nanometer scale. While crystalline nanomaterials have received a surge of attention for exhibiting state-of-the-art properties in various fields, their amorphous counterparts have also attracted attention in recent years owing to their unique structural features that crystalline materials lack. In short, amorphous nanomaterials only have short-range order at the atomic scale, and their atomic packing lacks long-range periodic arrangement, in which the coordinatively unsaturated environment, isotropic atomic structure, and modulated electron state all contribute to their outstanding performance in various applications. Given their intriguing characteristics, we herein present a series of representative works to elaborate on the structural advantages of amorphous nanomaterials as well as their enhanced electrocatalytic, surface-enhanced Raman scattering (SERS), and mechanical properties, thereby elucidating the underlying structure-function relationship. We hope that this proposed relationship will be universally applicable, thus encouraging future work in the design of amorphous materials that show promising performance in a wide range of fields.

Systematic Study of the Nanostructures of Exfoliated Polymer Nanocomposites.

High-performance bioinspired materials have shown rapid development over the last decade. Examples are brick-and-mortar hierarchical structures, which are often achieved via solvent evaporation. Although good properties are claimed, most systems are composed of stacked or intercalated platelets. Exfoliation is a crucial step to give ultimate anisotropic properties, e.g., thermal, mechanical, and barrier properties. We propose a general framework for all the various types of micro-scale structures that should be distinguished for 2D filler nanocomposites. In particular, the exfoliated state is systematically explored by the immobilization of montmorillonite platelets via (gelatin) hydrogelation. Scattering techniques were used to evaluate this strategy at the level of the particle dispersion and the regularity of spatial arrangement. The gelatin/montmorillonite exfoliated nanostructures are fully controlled by the filler volume fraction since the observed gallery d-spacings perfectly fall onto the predicted values. Surprisingly, X-ray analysis also revealed short- and quasi long-range arrangement of the montmorillonite clay at high loading.

Microstructure quantification of oblique angle sputtered porous a-Si thin films as a basis for structure-property relations of solid phase microextraction coatings

Understanding processing-structure-property (PSP) linkages of solid-phase microextraction (SPME) coating materials is crucial for the rational design and advancement of these new materials. As SPME is a diffusion-based extraction technique, analyzing the morphology of its coating materials is important for optimizing its performance. In this study, we assess the morphological evolution of micro/mesoporous amorphous silicon (a-Si) thin films sputtered at an oblique angle onto silicon, which serve as models for support materials in SPME devices. The contrast of scanning transmission electron microscopy (STEM) images is enhanced via ZnO infiltration by atomic layer deposition (ALD). Various metrics, including physical descriptors and two-point statistics methods, are employed to follow the films' evolution. Analysis of the two-point correlation function reveals a simple ellipse/spherical local pore geometry in contrast to the long-range irregular arrangement of pores identified by a range of traditional and novel metrics. Additionally, analyzing the internal structure of the pores through homology metrics aligns well with the theoretical understanding of morphological evolution in oblique sputtered films. These analyses show that the “average ratio of principal moment of inertia”, “Betti numbers”, and “two-point statistics” based metrics can capture valuable information during film growth.The morphological analysis approach proposed in this study can be applied to analyze any nanoporous medium as a first step towards developing structure-property relationships that tie back to a given preparation method. Ultimately, a more extensive experimental and/or simulation-based study should confirm the correlations between these metrics and actual diffusion properties as the basis for process-structure-properties relations for improved design and optimization of this film.

A critical evaluation of structural, optical, and gamma-ray attenuation properties of novel erbium (III) oxide-reinforced borosilicate barium glass system

A borosilicate barium glass series doped by erbium (III) oxide was fabricated using the conventional melt quenching technique with a melting temperature of 1100 °C and an annealing temperature of 400 °C. The x-ray diffraction pattern confirms that the glass samples are amorphous and have no long-range atomic arrangement. The densities of the borosilicate barium enhanced from 2.9749 g cm−3 to 3.0126 g cm−3 with an increasing Er2O3 substitution ratio. The UV–vis spectrum measurement showed an enhancement in the refractive index of the samples from 2.311 to 2.336. The γ-ray shielding properties of the fabricated glasses were estimated between 0.059 and 1.332 MeV. The obtained results showed an enhancement in the linear attenuation coefficient with increasing the Er2O3 substitution ratio to the borosilicate barium glass at low γ-photon energies while no considerable enhancement was achieved in the high and intermediate γ-photon energies. At γ-photon energy of 0.059 MeV, the linear attenuation coefficient was enhanced by a factor of ≈38%, while this ratio dropped to less than 10% for high and intermediate γ-photon energy. The mentioned results showed that the low concentrations of Er2O3 possess a significant enhancement in optical properties and low γ- ray shielding.

Role of Non-covalent Interaction toward Conductivity in a One-Dimensional Tube-like Silver-Thiolate Structure

We report a new one-dimensional tube-like atomically precise silver-thiolate polymer–chain. The structure consists of Ag14(SR)18 as the building units. Silver atoms are linked with the thiol ligand to form the one-dimensional structure. The non-covalent interactions like argentophilic and C–H···H–C interactions appear as crucial for the long-range structural arrangement. Electronic structure calculations show its semiconductor-type band structure with a band gap of about 2 eV. Conductivity measurements on the single crystal implies its facile charge transfer pathway along the one-dimensional chain. The variation of conductivity between the single crystal and the drop-cast film implies the role of argentophilic and C–H···H–C interactions in the preferred charge transfer pathway.

High entropy strategy on thermoelectric materials

High-entropy materials, which consist of multiple elements occupying a single sublattice in a disordered manner, have emerged as innovative material systems with various promising applications. Many macroscopic physical properties, such as electrical transport and thermal transport, are closely related to the periodic distribution of atoms. In high-entropy compounds, the long-range periodic arrangement of atoms is broken down by the disordered distribution of various elements, which would lead to changes in physical properties. Therefore, the high-entropy idea will open new avenues for designing these functional materials with promising performance and high reliability. This perspective focuses on the high-entropy strategies of thermoelectric materials, discussing how high entropy will alter their properties. The possible routes of designing high-entropy high-performance thermoelectric materials are prospected, which can also provide enlightenment for the development of high-entropy systems in other research fields.

Understanding the switching mechanism of oxygen-doped Sb phase-change material: Insights from first principles

The crystalline–amorphous–crystalline transition process of an oxygen-tuned Sb phase-change material has been obtained by employing ab initio molecular dynamic calculations. By analyzing the local atomic arrangement and the electron structure of the SbO system, the intrinsic mechanism is explored to comprehend the material function: (1) ultrafast crystallization and difficulty in creating a glassy state of a pure Sb material might be caused by the resonance bonding of linear arrangement Sb atoms in the rhombohedral phase; (2) the impurity oxygen atoms break the medium and long-range linear arrangement of the Sb network by steric effects and change the electronic structure of these Sb atoms bonded to oxygen atoms, i.e., the obvious increase in electron localization and the great decrease in state distribution around the Fermi surface due to the high electronegativity of oxygen. These factors set an effective barrier for crystallization and improve the amorphous stability and, thus, data retention. The present research and scheme provide important insights into the engineering and manipulation of a phase-change material through first-principles calculations toward non-volatile phase change memory.

Shaping a Doped Perovskite Oxide with Measured Grain Boundary Defects to Catalyze Bifunctional Oxygen Activation for a Rechargeable Zn-Air Battery.

Symmetry broken configurations within a long-range atomic arrangement exhibit new physical properties, and distinctive strategies are needed to resuscitate the localized symmetry by introducing measured defects, which can be attractive in displaying enhanced catalytic activities for energy applications. Our hypothesis is validated by introducing lattice defects due to the strain originating from a slightly higher doped grain boundary (GB) than at the interconnected grains of perovskite oxide. When Pd is doped at the B-site of ABO3-type La0.7Sr0.3CoO3-δ, a marginally higher ionic radius of Pd4+ than Co3+ enables partial deportation of Pd4+ to the GB. Consequently, the GB unit cell is relatively expanded with a higher interplanar spacing, as observed by microscopic analysis. When the Pd concentration is increased, oxygen vacancy sites are reduced and both metallic Pd and PdOx are exsolved at the perovskite oxide surface. With the Pd/Co ratio of 0.05, the defects originating from the Pd-modulated GB can be maximized to 1.29 ± 0.21% which enhances the bifunctional O2 activation ability by lowering the combined overpotential of oxygen evolution and reduction reactions (OER/ORR) to 0.91 V, duly corroborated by computational studies. The fabricated rechargeable Zn-air battery has a specific capacity of 740 mA·h/gZn (851 mW·h/gZn) when discharge is performed at 10 mA/cm2. Galvanostatic charge-discharge cycling with a 1 h cycle time shows 60 h stable performance. The OER/ORR bifunctional activity is found to be strongly correlated to the repositioned lattice symmetry at the perovskite GB.

Alkali halide tailored graphitic carbon nitride with an extended optical absorbance for solar photocatalytic degradation of phenol

The structural, optical, textural, and photocatalytic properties of graphitic carbon nitride (g-C3N4) has been modified thru the elemental doping with Sodium and potassium salts. The skeletal distortion of g-C3N4 enables the tuning of electronic structure and positions of valence and conduction band. It also has reduced the charge separation rate, which activates the n-π* transitions resulting in an improved light absorption capacity. Furthermore, the +1 oxidation state of Na and K has incorporated in the structure of g-C3N4 and reduces the in-plane long-range periodic arrangement. Though there was no significant change in surface area was observed, but these factors govern an improved photocatalytic performance for phenolic effluent degradation in natural solar light, the current experimental studies indicate that slight acidic condition, i.e., pH 5 with 800 mg/L chemical oxidant dose at 4 L/h of effluent flow denotes 91.25, and 86.30% degradation of phenol, while in case of g-C3N4 it was 67.95%.

Chemical Solution Deposition of Ordered 2D Arrays of Room-Temperature Ferrimagnetic Cobalt Ferrite Nanodots.

Over the past decades, the development of nano-scale electronic devices and high-density memory storage media has raised the demand for low-cost fabrication methods of two-dimensional (2D) arrays of magnetic nanostructures. Here, we present a chemical solution deposition methodology to produce 2D arrays of cobalt ferrite (CFO) nanodots on Si substrates. Using thin films of four different self-assembled block copolymers as templates, ordered arrays of nanodots with four different characteristic dimensions were fabricated. The dot sizes and their long-range arrangement were studied with scanning electron microscopy (SEM) and grazing incident small-angle X-ray scattering (GISAXS). The structural evolution during UV/ozone treatment and the following thermal annealing was investigated through monitoring the atomic arrangement with X-ray absorption fine structure spectroscopy (EXAFS) and checking the morphology at each preparation step. The preparation method presented here obtains array types that exhibit thicknesses less than 10 nm and blocking temperatures above room temperature (e.g., 312 K for 20 nm diameter dots). Control over the average dot size allows observing an increase of the blocking temperature with increasing dot diameter. The nanodots present promising properties for room temperature data storage, especially if a better control over their size distribution will be achieved in the future.

Ubiquitous energy conversion of two-dimensional molecular crystals

Two-dimensional (2D) atomic crystals have triggered significant excitement due to their rich physics as well as potential industrial applications. The possibility of a molecular counterpart with scalable processability and superior performance is intriguing from both fundamental and applied perspectives. Here, we present the freestanding 2D molecular charge-transfer bis(ethylenedithio)tetrathiafulvalene-C60 crystals prepared by a modified Langmuir–Blodgett method, with precisely controlled few-layer thickness and centimeter-scale lateral dimension. The interconversion of intrinsic excited process, the long-range ordering and anisotropic stacking arrangement of the molecular layered crystals generate external stimuli responsive behaviors and anisotropic spin-charge conversion with magnetic energy conversion ability, as well as a superior UV photosensitivity. Moreover, the 2D freestanding crystals demonstrate superior magneto-electrical properties. These results suggest that a new class of 2D atomically thin molecular crystals with novel electronic, optical and magnetic properties have great potential for spintronic, energy and sensor applications.

SERS effect of Rhodamine 6G molecular probe on AgAu alloy nanowire arrays by a solid-state ionics method

AgAu alloy nanowire arrays were prepared by a solid-state ionics method under a direct current electric field (DCEF) using fast ionic conductor RbAg4I5 films. The surface morphology and chemical composition of the AgAu alloy nanowire arrays were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), respectively. Raman enhancement performance of the AgAu alloy nanowire arrays substrates was detected by Rhodamine 6G (R6G) aqueous solutions as molecular probe. Long-range order and short-range order AgAu alloy nanowire arrays with the length of 1 cm were prepared by a solid-state ionics method. The nanowires were bamboo-shaped and the diameters of nanowires ranged from 20 to 80 nm. The molar ratio of Ag to Au is 15:1. The limiting concentrations of R6G for the prepared AgAu alloy nanowire arrays SERS substrates is 10−17 mol/L. The long-range and short-range orderly arrangement, high roughness and alloy structure of AgAu alloy nanowire arrays result in the substantial SERS effect.

NiMo catalysts supported on Al, Nb, Ti or Zr-containing MCM-41 for dibenzothiophene hydrodesulfurization

xMCM-41 materials (x = Al, Nb, Ti or Zr) with nominal x loading of 0.5 mmol/g were prepared by chemical grafting of Al2O3, Nb2O5, TiO2 and ZrO2 precursors and used as supports for NiMo/xMCM-41 catalysts. Small-angle XRD characterization of supports showed typical patterns of solids with hexagonal arrangement of mesopores. After the deposition of Ni and Mo oxide species on the supports a decrease in their long-range pore arrangement was observed. Nevertheless, the prepared NiMo catalysts possessed high specific surface areas and pore volumes. Powder XRD patterns showed the formation of the MoO3 crystalline phase in the NiMo/MCM-41 reference. This phase was not detected in the catalysts supported on xMCM-41 materials. An increase in the dispersion of MoO3 species with the incorporation of alumina, niobia, titania and zirconia in the MCM-41 support was due to the stronger interaction of Mo and Ni oxide species with xMCM-41 materials (H2-TPR and UV–vis DRS). Surface modification of the MCM-41 with different metal oxides increased the dibenzothiophene conversion and pseudo first-order rate constants. This effect was more evident for the NiMo/TiMCM-41 catalyst. Selectivity of the catalysts (product distributions) was also affected by the incorporation of Al-, Zr-, Ti- and Nb-oxide species in the support.

Temperature dependence of exchange biased multiferroic BiFeO3/Ni81Fe19 polycrystalline bilayer

The temperature dependence of exchange bias properties are studied in polycrystalline bilayers, for different thicknesses. Using a field cooling protocol, a non-monotonic behavior of the exchange bias field is shown in the exchange-biased bilayers. Another thermal protocol, the Soeya protocol, related to the thermal activation energies was carried out and reveals a two-step evolution of the exchange bias field. The results of these two different protocols are similar to the ones obtained for measurements previously reported on epitaxial , indicating a driving mechanism independent of the long-range crystalline arrangement (i.e. epitaxial or polycrystalline). An intrinsic property of is proposed as being the driving mechanism for the thermal dependent magnetization reversal: the canting of the spins leading to a biquadratic contribution to the exchange coupling. The temperature dependence of the magnetization reversal angular behavior agrees with the presence of such a biquadratic contribution for exchange biased bilayers studied here.

How a Small Structural Difference Can Turn Optical Properties of π-Extended Coumarins Upside Down: The Role of Non-Innocent Saturated Rings.

The fluorescence properties of two new families of heterocycles possessing either a seven- or five-membered ring attached at the core molecule are entirely different in solution and in the solid state. Crystallization has the effect of inhibiting non-radiative excited-state deactivation pathways, operative in solution for the seven-membered ring compounds, thus leading to significant fluorescence efficiency in the solid state, with quantum yields ranging from 0.10 to 0.36. Conversely, the five-membered ring derivatives, which display notable emission properties in solution, are almost non-emissive in the crystalline state, characterized by a long-range π-stacked arrangement. When embedded in polymeric films, both series show fluorescence features similar to the solution case, with remarkable fluorescence quantum yields ranging from 0.09 to 0.41. According to quantum chemical calculations, 3H-chromeno[3,4-c]pyridine-4,5-diones show the specific mechanism of fluorescence quenching. The derivatives bearing the seven-membered ring undergo, in solution, a significant structural deformation in the excited state, resulting in a large decrease of the energy gap between S1 and S0 and hence to a substantial contribution of the internal conversion in the relaxation process. The fluorescence quenching of the five-membered ring derivatives is in turn related to the intermolecular interaction between adjacent molecules prevailing to a greater extent in the crystal lattice.

Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and abinitio Theory.

We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ∼1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Abinitio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by abinitio theory.

Long-Range Hexagonal Arrangement of TiO2 Nanotubes by Soft Lithography-Guided Anodization

Long range hexagonally ordered TiO2 nanotube arrangements have been synthesized by employing a novel strategy consisted of combining the well-known Laser Interference Lithography technique together with electrochemical anodization methods. By properly tuning the fabrication parameters that make match between both techniques, TiO2 nanotube arrays having near 32nm of inner diameter, wall thickness around of 25nm and 210nm of lattice parameter were anodically grown on pre-patterned Ti foils over large sample surface areas, typically of several squared centimetres in size. This opens the possibility to the development of new types of functional devices based on self-organized morphologies of anodic TiO2 nanotubes, requiring both high spatially ordered and defect-free nanotube arrangements.