Nanoscale Structural Heterogeneity Research Articles

A Fluorescent Sensor for Quantitative Super‐Resolution Imaging of Amyloid Fibril Assembly**

AbstractMany soluble proteins can self‐assemble into macromolecular structures called amyloids, a subset of which are implicated in a range of neurodegenerative disorders. The nanoscale size and structural heterogeneity of prefibrillar and early aggregates, as well as mature amyloid fibrils, pose significant challenges for the quantification of amyloid morphologies. We report a fluorescent amyloid sensor AmyBlink‐1 and its application in super‐resolution imaging of amyloid structures. AmyBlink‐1 exhibits a 5‐fold increase in ratio of the green (thioflavin T) to red (Alexa Fluor 647) emission intensities upon interaction with amyloid fibrils. Using AmyBlink‐1, we performed nanoscale imaging of four different types of amyloid fibrils, achieving a resolution of ≈30 nm. AmyBlink‐1 enables nanoscale visualization and subsequent quantification of morphological features, such as the length and skew of individual amyloid aggregates formed at different times along the amyloid assembly pathway.

Effects of annealing time on nanoscale structural heterogeneity and magnetic properties of Fe<sub>80</sub>Si<sub>9</sub>B<sub>10</sub>Cu<sub>1</sub> amorphous alloy

The evolution of nanoscale structural heterogeneity and its effect on magnetic properties of Fe<sub>80</sub>Si<sub>9</sub>B<sub>10</sub>Cu<sub>1</sub> amorphous alloy during structural relaxation after being annealed for different times are investigated in this work. The nanoscale structural heterogeneity is found to degenerate gradually with relaxation by using the small-angle X-ray scattering and atomic force microscope. Combined with Mössbauer spectroscopy analysis results, the enhanced comprehensive soft magnetic properties of the relaxed alloys can be attributed to the degeneration of nanoscale structural heterogeneity. From the flow unit model, the volume fraction of flow units decreases with relaxation proceeding, and some of the flow units annihilate and transform into the ideal elastic matrix. On the one hand, the relaxed sample with greater packing density has stronger magnetic exchange interaction and higher saturation magnetic flux intensity. On the other hand, the number density of quasi-dislocation dipoles decreases with the annihilation of flow units in the relaxation process, leading the pinning effect of the domain wall to be weakened. Consequently, the magnetic anisotropy decreases after relaxation, which results in the reduction of coercivity. In this work, the structural mechanism of the evolution of magnetic properties in the relaxation process of Fe<sub>80</sub>Si<sub>9</sub>B<sub>10</sub>Cu<sub>1</sub> amorphous alloy is investigated from the perspective of structural heterogeneity, which is helpful in establishing the correlation between the structure and magnetic properties of Fe-based amorphous alloys.

Characterization of nanoscale structural heterogeneity in metallic glasses: A machine learning study

Atomic force microscopy (AFM) is an efficient tool for studying the structural heterogeneity in metallic glasses (MGs). However, time-consuming analysis and limitations in the scanning process are downsides of this experiment. To tackle these problems, a machine learning (ML) model was developed to predict the distribution of energy dissipation on the MG surface with the increase in number of AFM scanning. The results indicated that it was possible to accurately predict the energy of scanning points, leading to a timesaving and reliable study. Moreover, characterization of structural heterogeneity shows that the viscoelastic response of each nanoscale region under sequences of AFM scans depends on the initial energy state. The predictive results unfold that the high-dissipated regions show a stochastic trend, while the regions with moderate energy level tend to exhibit a regular behavior. The low-dissipated regions also resist to the significant energy variations, which is due to their interconnected nanostructure.

Nanoscale structural heterogeneity perspective on the improved magnetic properties during relaxation in a Fe-based metallic glass

Despite the mesoscopic isotropic nature of metallic glasses, there is a certain degree of structural heterogeneity down to the nanoscale. However, how structural heterogeneity affects the magnetic properties is still unclear. In this work, the relaxation-induced structural heterogeneity and magnetic properties evolution of Fe80Si9B11 metallic glass were investigated by atomic force microscopy (AFM) and Mössbauer spectroscopy. We revealed that the correlation-length of nanoscale heterogeneity relates closely with the ferromagnetic exchange interaction together with the magnetic anisotropy, providing experimental evidence of the intrinsic link between the nanoscale structural heterogeneity and magnetic properties for Fe-based metallic glasses. The degeneration of nanoscale structural heterogeneity induces the enhancement of the ferromagnetic exchange interaction and weakening of the magnetic anisotropy. Our results have a vital significance in understanding the structure-property relationship of metallic glass.

Direct observation of nanocrystal-induced enhancement of tensile ductility in a metallic glass composite

Bulk metallic glasses (BMGs) have attracted wide interest, but their successful application is hindered by their low ductility at room temperature. Therefore, the use of composites of a BMG matrix with crystalline secondary phases has been proposed to overcome this drawback. In the present work we demonstrate the fabrication of a tailored BMG nanocomposite containing a high density of monodisperse nanocrystals with a size of around 20 nm using a combination of mechanical and thermal treatment of Cu36Zr48Al8Ag8 well below the crystallization temperature. Direct observations of the interaction of the nanocrystals with a shear band during in situ deformation in a transmission electron microscope demonstrate that the achieved nanocomposite has the potential to inhibit catastrophic fracture in tension. This demonstrates that a sufficient number of nanoscale structural heterogeneities can be a route towards BMG composites with superior mechanical properties.

In situ neutron scattering studies of a liquid–liquid phase transition in the supercooled liquid of a Zr–Cu–Al–Ag glass-forming alloy

The presence of a liquid–liquid phase transition in the supercooled-liquid temperature range for a glass-forming Zr–Cu–Al–Ag alloy has been revealed using a suite of in situ neutron scattering techniques, including small-angle neutron scattering (SANS) and total neutron scattering. The SANS data analysis is indicative of the enhancement of nanoscale structural heterogeneities prior to crystallization, which is further supported by the total scattering result that points to an increase in the degree of medium-range ordering during the transition. In addition, a calorimetric anomaly and abnormal thermal expansion behavior were also observed upon heating. As such, this study provides multiscale structural evidence on the liquid–liquid phase transition and helps to gain insight into its underlying mechanism in terms of cluster connectivity.

Distilling nanoscale heterogeneity of amorphous silicon using tip-enhanced Raman spectroscopy (TERS) via multiresolution manifold learning

Accurately identifying the local structural heterogeneity of complex, disordered amorphous materials such as amorphous silicon is crucial for accelerating technology development. However, short-range atomic ordering quantification and nanoscale spatial resolution over a large area on a-Si have remained major challenges and practically unexplored. We resolve phonon vibrational modes of a-Si at a lateral resolution of <60 nm by tip-enhanced Raman spectroscopy. To project the high dimensional TERS imaging to a two-dimensional manifold space and categorize amorphous silicon structure, we developed a multiresolution manifold learning algorithm. It allows for quantifying average Si-Si distortion angle and the strain free energy at nanoscale without a human-specified physical threshold. The multiresolution feature of the multiresolution manifold learning allows for distilling local defects of ultra-low abundance (< 0.3%), presenting a new Raman mode at finer resolution grids. This work promises a general paradigm of resolving nanoscale structural heterogeneity and updating domain knowledge for highly disordered materials.

Effects of minor Si addition on structural heterogeneity and glass formation of GdDyErCoAl high-entropy bulk metallic glass

Glass-forming ability (GFA) of the Gd20Dy20Er20Co20Al20 high-entropy bulk metallic glass (HE-BMG) was improved through microalloying Si element. The critical diameter of this rare-earth-based HE-BMG increases from 1.5 to 8.5 mm with 0.5 at.% Si addition without any deterioration of magnetocaloric property. Compared with the Si-free sample, the BMG with 0.5 at.% Si addition exhibits low driving force for crystallization, strong supercooled liquid behavior and sluggish crystallization kinetics, whereas excessive Si addition leads to reverse variations. Furthermore, microalloying Si can enhance nanoscale heterogeneity of elemental distribution, and thus facilitates the formation of local crystal-like structures. The connectivity and competition between icosahedra-like clusters and crystal-like structures promote the formation of stable network structure which frustrates crystallization. As Si content is excessive, icosahedra-like cluster is consumed by the further grown crystal-like structure, leading to the destruction of network and decreasing GFA. This work not only elucidates the underlying mechanism of the GFA enhanced by microalloying, but also sheds light on improving the GFA of HE-BMGs through altering nanoscale elemental distribution and structural heterogeneity.

Rapid Structural, Kinetic, and Immunochemical Analysis of Alpha-Synuclein Oligomers in Solution.

Oligomers comprised of misfolded proteins are implicated as neurotoxins in the pathogenesis of protein misfolding conditions such as Parkinson's and Alzheimer's diseases. Structural, biophysical, and biochemical characterization of these nanoscale protein assemblies is key to understanding their pathology and the design of therapeutic interventions, yet it is challenging due to their heterogeneous, transient nature and low relative abundance in complex mixtures. Here, we demonstrate separation of heterogeneous populations of oligomeric α-synuclein, a protein central to the pathology of Parkinson's disease, in solution using microfluidic free-flow electrophoresis. We characterize nanoscale structural heterogeneity of transient oligomers on a time scale of seconds, at least 2 orders of magnitude faster than conventional techniques. Furthermore, we utilize our platform to analyze oligomer ζ-potential and probe the immunochemistry of wild-type α-synuclein oligomers. Our findings contribute to an improved characterization of α-synuclein oligomers and demonstrate the application of microchip electrophoresis for the free-solution analysis of biological nanoparticle analytes.

Structural Heterogeneity, Ductility, and Glass Forming Ability of Zr-Based Metallic Glasses

We show the correlation between nanoscale structural heterogeneity, mechanical property, and glass-forming ability of Zr-Cu-Co-Al metallic glasses (MGs). Local regions with medium-range ordering (MRO) were directly visualized in electron dark-field images of (Zr 45 Cu 50 Al 5 ) 1- x (Zr 55 Co 25 Al 20 ) x MGs acquired using 4-dimensional scanning transmission electron microscopy (4D-STEM), which enables determination of the type, size, and volume fraction of MRO domains with high precision and statistical reliability. Angular correlation analysis of 4D-STEM data shows notable differences in MRO types between x = 0 and x = 1, and certain types of MRO involve structural frustration that correlates to high glass-forming ability. More importantly, the smaller and more diverse MRO at x = 0.5 correlates with a substantial increase in ductility, suggesting a potential role of MRO in the deformation of MGs. Mesoscale deformation simulation incorporating the experimentally determined MRO confirms that the diverse types and sizes of MRO can significantly influence the MGs’ mechanical behavior, which we attribute to the strain frustration mechanism due to increased heterogeneity.

An atomic-level perspective of shear band formation and interaction in monolithic metallic glasses

Understanding the relationship between nanoscale structural heterogeneities or elastic fluctuations and strain localization in monolithic metallic glasses remains a long-standing underlying issue. Here, an atomic-level investigation of the correlation between elastic and structural heterogeneities and the mechanisms of shear banding in CuZr metallic glass is conducted using molecular dynamics simulations. The shear band formation and propagation processes and the intersection mechanism of multiple shear bands are evaluated by means of local entropy-based structural identification and von Mises stress calculation. The shear band follows the path of lower order and high entropy while shear deflection and branching occur when approaching regions of low entropy. The local von Mises stress calculation allows predictions on the shear band direction and the propensity for activation and propagation prior to yielding and sheds light on shear band branching and multiplication processes.

Atomic-resolution electron microscopy of nanoscale local structure in lead-based relaxor ferroelectrics

Relaxor ferroelectrics, which can exhibit exceptional electromechanical coupling, are some of the most important functional materials, with applications ranging from ultrasound imaging to actuators. Since their discovery, their complex nanoscale chemical and structural heterogeneity has made the origins of their electromechanical properties extremely difficult to understand. Here, we employ aberration-corrected scanning transmission electron microscopy to quantify various types of nanoscale heterogeneities and their connection to local polarization in the prototypical relaxor ferroelectric system Pb(Mg1/3Nb2/3)O3-PbTiO3. We identify three main contributions that each depend on Ti content: chemical order, oxygen octahedral tilt and oxygen octahedral distortion. These heterogeneities are found to be spatially correlated with low-angle polar domain walls, indicating their role in disrupting long-range polarization and leading to nanoscale domain formation and the relaxor response. We further locate nanoscale regions of monoclinic-like distortion that correlate directly with Ti content and electromechanical performance. Through this approach, the connections between chemical heterogeneity, structural heterogeneity and local polarization are revealed, validating models that are needed to develop the next generation of relaxor ferroelectrics.

Phase separation-induced nanoscale heterogeneity in Gd5Si1.5Ge2.5

Pseudobinary Gd5(Si,Ge)4 compounds show a giant magnetocaloric effect due to an intriguing structure-magnetism interplay. Here, we report a high resolution transmission electron microscopic study of microstructure in a melt-grown compound of Gd5Si1.5Ge2.5. Electron diffraction showed that mesoscopic microstructure of the compound consists of crystals of a monoclinic structure and two kinds of orthorhombic structure. However, atomic-level imaging revealed a coexistence of mosaic-like nanodomains of these structures in each crystal. The nanodomains have twin-like interfaces along the b axis of the crystal but have semicoherent interfaces along a perpendicular axis due to stacking faults. Such a nanoscale structural heterogeneity is due to covalent bond-controlled phase separation at elevated temperatures. This finding offers insights into phase relations and abnormal magnetic behavior of Gd5(Si,Ge)4 compounds and points out a route of synthesizing bulk nanocomposites via nanoscale phase separation.

Enhancing the plasticity of a Ti-based bulk metallic glass composite by cryogenic cycling treatments

Abstract The effect of cryogenic cycling treatments on the thermal and mechanical properties of a Ti-based bulk metallic glass (BMG) composite was investigated. Even though the macroscopic structures of the dendrite-phase and glass-matrix remain unchanged, the treated samples exhibited a rejuvenation behavior in terms of a higher relaxation enthalpy, which leads to an enhancement of plasticity as high as 90%. Different from the monolithic BMGs, in which rejuvenation has been attributed to the nanoscale structural heterogeneity, rejuvenation in BMG composite is induced by the crystal/amorphous heterogeneous microstructures. The increasing defects around the interfaces may promote formation of multiple shear bands and accommodation of plastic deformation. This work shows clearly that the cryogenic cycling treatments could be an effective and controllable way to modulate mechanical properties of BMG composites.

Butterfly-wing hierarchical metallic glassy nanostructure for surface enhanced Raman scattering

The surface-enhanced Raman spectroscopy (SERS) is a technique for the detection of analytes on the surface with an ultrahigh sensitivity down to the atomic-scale, yet the fabrication of SERS materials such as nanoparticles or arrays of coinage metals often involve multiple complex steps with the high cost and pollution, largely limiting the application of SERS. Here, we report a complex hierarchical metallic glassy (MG) nanostructure by simply replicating the surface microstructure of butterfly wings through vapor deposition technique. The MG nanostructure displays an excellent SERS effect and moreover, a superhydrophobicity and self-cleaning behavior. The SERS effect of the MG nanostructure is attributed to the intrinsic nanoscale structural heterogeneities on the MG surface, which provides a large number of hotspots for the localized electromagnetic field enhancement affirmed by the finite-difference time-domain (FDTD) simulation. Our works show that the MG could be a new potential SERS material with low cost and good durability, well extending the functional application of this kind of material.

Atomic-scale viscoplasticity mechanisms revealed in high ductility metallic glass films

The fundamental plasticity mechanisms in thin freestanding Zr65Ni35 metallic glass films are investigated in order to unravel the origin of an outstanding strength/ductility balance. The deformation process is homogenous until fracture with no evidence of catastrophic shear banding. The creep/relaxation behaviour of the films was characterized by on-chip tensile testing, revealing an activation volume in the range 100–200 Å3. Advanced high-resolution transmission electron microscopy imaging and spectroscopy exhibit a very fine glassy nanostructure with well-defined dense Ni-rich clusters embedded in Zr-rich clusters of lower atomic density and a ~2–3 nm characteristic length scale. Nanobeam electron diffraction analysis reveals that the accumulation of plastic deformation at room-temperature correlates with monotonously increasing disruption of the local atomic order. These results provide experimental evidences of the dynamics of shear transformation zones activation in metallic glasses. The impact of the nanoscale structural heterogeneities on the mechanical properties including the rate dependent behaviour is discussed, shedding new light on the governing plasticity mechanisms in metallic glasses with initially heterogeneous atomic arrangement.

Diffusional Dynamics of Tetraalkylphosphonium Ionic Liquid Films Measured by Fluorescence Correlation Spectroscopy.

Fluorescence correlation spectroscopy (FCS) is applied to investigate the diffusional dynamics of hydrophilic (Atto 590) and amphiphilic (DiD) fluorophores in a series of alkylphosphonium ionic liquid (IL) films ([P4448][Cl], [P6668][Cl], [P66614][Cl], and [P66614][NTf2]) in order to determine diffusional parameters and to elucidate nanoscale structural heterogeneities within the IL. From the measured correlation functions, the diffusion coefficients of the fluorescent molecules are estimated, rendering values that span from 0.39 to 1.2 and 0.146 to 5.2 μm2/s for Atto 590 and DiD, respectively. An increase in the diffusion coefficient values is correlated to the increase in the alkyl chain length, which in turn is correlated with a decrease in their viscosity. Interestingly, deviations from Brownian diffusion behavior of the fluorescent probes in the ILs are observed, showing a time-dependent diffusion coefficient in most of the cases. These deviations can be attributed to the presence of nanoscale structural heterogeneities in the tetraalkylphosphonium ILs. These results experimentally confirm the presence of nanosegregation in tetraalkylphosphonium ILs, which has been previously observed in molecular dynamics studies.

Effect of Polymerized Ionic Liquid Structure and Morphology on Shockwave Energy Dissipation.

The ability of nanosegregated polymerized ionic liquids (PILs) to dissipate shockwave energy is investigated for a series of imidazolium-based PILs with varying alkyl spacer length. The PILs are designed to have similar glass transition temperatures but different structures. X-ray scattering analysis reveals that each of the amorphous PILs exhibit distinct nanoscale structural heterogeneity, depending on the length of the chain spacer. We find that a higher structural heterogeneity, determined from the intensity of the intercluster scattering peak, in the PILs with longer alkyl spacers results in greater shockwave energy dissipation. In addition, we observe the crystalline phase is less effective at dissipating shockwave energy than the amorphous phase due to the close packed morphology and slow kinetics.

Dilatancy signatures of amorphous plasticity probed by X-ray synchrotron radiation

The dilatancy signatures associated with the plastic deformation of a typical Zr-based amorphous alloy are captured by using synchrotron radiation X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) techniques. XRD demonstrates that the right-subpeak atoms of the second coordination shell accommodate the local dilatation, which occurs prior to the plastic yielding and during the softening-to-flow transition process. Mediated by the local dilatation, local atomic rearrangements can operate at the left-subpeak of the second shell and/or at the fourth shell with a characteristic lengthscale of about 1 nm. The obtained dilatancy signatures of amorphous plasticity are further confirmed by SAXS in terms of the nano-scale structural heterogeneity.

Guest Vapor-Induced State Change of Structural Liquid Pillar[6]arene.

State change is a key phenomenon in materials science. We report the first observation of vapor-responsive reversible structural liquid-to-solid and solid-to-structural liquid state changes. We observed that a macrocyclic compound, a pillar[6]arene derivative bearing 12 n-hexyl substituents, is a room temperature structural liquid with unique properties. Formation of a host-guest complex between the pillar[6]arene cavity and the n-hexyl substituent results in a structural liquid with nanoscale structural heterogeneities. The structural liquid solidifies when exposed to competitive cyclohexane guest vapor, whereupon cyclohexane replaces the n-hexyl substituents in the pillar[6]arene cavity and the n-hexyl substituents located outside of the cavity crystallize into distinct nanolayer assemblies. The solid reverts back to the structural liquid when the cyclohexane guest is removed through heating under reduced pressure because of rethreading of the n-hexyl substituents into the cavity. The structural liquid-to-solid and solid-to-structural liquid changes are reversible through the uptake and release of cyclohexane guest vapor.