Unveiling the Structural Origins of Dynamic Diversity in Pd-Based Metallic Glasses.

The ß-relaxation is one of the major dynamic behaviors in metallic glasses (MGs) and exhibits diverse features. Despite decades of efforts, the understanding of its structural origin and contribution to the overall dynamics of MG systems is still unclear. Here two palladium-based Pd─Cu─P and Pd─Ni─P MGs are reported with distinct different ß-relaxation behaviors and reveal the structural origins for the difference using the advanced X-ray photon correlation spectroscopy and absorption fine structure techniques together with the first-principles calculations. The pronounced ß-relaxation and fast atomic dynamics in the Pd─Cu─P MG mainly come from the strong mobility of Cu atoms and their locally favored structures. In contrast, the motion of Ni atoms is constrained by P atoms in the Pd─Ni─P MG, leading to the weakened ß-relaxation peak and sluggish dynamics. The correlation of atomic dynamics with microscopic structures provides a way to understand the structural origins of different dynamic behaviors as well as the nature of aging in disordered materials.

Identification of Novel Biomarkers for Abdominal Aortic Aneurysm Promoted by Obstructive Sleep Apnea.

BACKGROUND: We sought to find new biomarkers for abdominal aortic aneurysms (AAA) caused by chronic intermittent hypoxia (CIH). METHODS: The AAA mice model was created using Ang II. The mice were divided into normoxic and CIH groups. The structure of AAA was observed using abdominal ultrasonography, Elastica van Gieson (EVG), and hematoxylin and eosin (HE) staining. The expression of ɑ-SMA was investigated using immunohistochemistry. The novel biomarkers were screened using bioinformatics analysis. Quantitative real-time polymerase chain reaction (qRT-PCR) was employed to verify the expression of novel genes in both normal oxygen and CIH. RESULTS: CIH appears to cause greater aortic dilation, higher AAA incidence, lower survival rate, thicker vessel wall, and more brittle elastic lamellae when compared to controls. The immunohistochemistry results showed that the expression of ɑ-SMA in the CIH group was reduced significantly. Four novel genes, including Homer2, Robo2, Ehf, and Asic1, were found to be differentially expressed between normal oxygen and CIH using qRT-PCR, indicating the same trend as bioinformatics analysis. CONCLUSIONS: We discovered that CIH could hasten the occurrence and progression of AAA. Four genes (Homer2, Robo2, Ehf, and Asic1) may be novel biomarkers for AAA, which could aid in the search for new therapies for patients with AAA caused by CIH.

Fabrication and optical behavior of AuCuSi amorphous alloy film.

Amorphous alloys (AAs) are promising materials due to their unique properties and have been applied in various biomaterial coatings and micro-electro-mechanical systems. However, they have seldom been applied in the optical nano-device. Here, we systematically investigate morphology, microstructure, mechanical and optical properties of an Au-Cu-Si AA and successfully design and fabricate a broadband optical absorber using the Au-Cu-Si AA. Such device achieves an average absorption up to about 95% from 500 to 1500 nm with a thickness less than 300 nm. This is of significance for exploration the feasibility of AAs application in the field of optical nano-devices.

High throughput fabrication of large-area plasmonic color filters by soft-X-ray interference lithography.

Plasmonic color filters in mass production have been restricted from current fabrication technology, which impede their applications. Soft-X-ray interference lithography (XIL) has recently generated considerable interest as a newly developed technique for the production of periodic nano-structures with resolution theoretically below 4 nm. Here we ameliorate XIL by adding an order sorting aperture and designing the light path properly to achieve perfect-stitching nano-patterns and fast fabrication of large-area color filters. The fill factor of nanostructures prepared on ultrathin Ag films can largely affect the transmission minimum of plasmonic color filters. By changing the fill factor, the color can be controlled flexibly, improving the utilization efficiency of the mask in XIL simultaneously. The calculated data agree well with the experimental results. Finally, an underlying mechanism has been uncovered after systematically analyzing the localized surface plasmon polaritons (LSPPs) coupling in electric field distribution.

Negative expansions of interatomic distances in metallic melts.

When a material is heated, generally, it dilates. Here, we find a general trend that the average distance between a center atom and atoms in the first nearest-neighbor shell contracts for several metallic melts upon heating. Using synchrotron X-ray diffraction technique and molecular dynamics simulations, we elucidate that this anomaly is caused by the redistribution of polyhedral clusters affected by temperature. In metallic melts, the high-coordinated polyhedra are inclined to evolve into low-coordinated ones with increasing temperature. As the coordination number decreases, the average atomic distance between a center atom and atoms in the first shell of polyhedral clusters is reduced. This phenomenon is a ubiquitous feature for metallic melts consisting of various-sized polyhedra. This finding sheds light on the understanding of atomic structures and thermal behavior of disordered materials and will trigger more experimental and theoretical studies of liquids, amorphous alloys, glasses, and casting temperature effect on solidification process of crystalline materials.

Electronic structure of carbon dioxide under pressure and insights into the molecular-to-nonmolecular transition.

Knowledge of the high-pressure behavior of carbon dioxide (CO2), an important planetary material found in Venus, Earth, and Mars, is vital to the study of the evolution and dynamics of the planetary interiors as well as to the fundamental understanding of the C-O bonding and interaction between the molecules. Recent studies have revealed a number of crystalline polymorphs (CO2-I to -VII) and an amorphous phase under high pressure-temperature conditions. Nevertheless, the reported phase stability field and transition pressures at room temperature are poorly defined, especially for the amorphous phase. Here we shed light on the successive pressure-induced local structural changes and the molecular-to-nonmolecular transition of CO2 at room temperature by performing an in situ study of the local electronic structure using X-ray Raman scattering, aided by first-principle exciton calculations. We show that the transition from CO2-I to CO2-III was initiated at around 7.4 GPa, and completed at about 17 GPa. The present study also shows that at ~37 GPa, molecular CO2 starts to polymerize to an extended structure with fourfold coordinated carbon and minor CO3 and CO-like species. The observed pressure is more than 10 GPa below previously reported. The disappearance of the minority species at 63(± 3) GPa suggests that a previously unknown phase transition within the nonmolecular phase of CO2 has occurred.

Angle-insensitive plasmonic color filters with randomly distributed silver nanodisks.

Plasmonic color filters inherently suffer from angular sensitiveness, which hinder them from practical applications. Here, we present a plasmonic subtractive color filter incorporating two-dimensional randomly distributed silver nanodisks on top of a glass substrate. Due to the elimination of structural periodicity, the proposed plasmonic color filter works via localized surface plasmon resonances (LSPRs) and thus enables excellent angle-insensitive (up to 60°) performance. In addition, uncoupled LSPRs between nanodisks guarantee stability and reproducibility of the color filter. Finally, a palette of colors across the visible region was obtained with the proposed color filters by simply varying the diameter of nanodisks, exhibiting a promising and robust applicability in digital imaging and sensing industries.

Exploring the nature of the liquid-liquid transition in silicon: a non-activated transformation.

In contrast to other glass formers, silicon exhibits a thermodynamic discontinuity between its liquid and amorphous solid states. Some researchers have conjectured that a first-order phase transition occurs between two forms of liquid silicon: the high-density liquid (HDL) and the low-density liquid (LDL). Despite the fact that several computer simulations have supported a liquid-liquid phase transition (LLPT) in silicon, recent work based on surface free energy calculations contradicts its existence and the authors of this work have argued that the proposed LLPT has been mistakenly interpreted [J. Chem. Phys., 2013, 138, 214504]. A similar controversy has also arisen in the case of water because of discrepancies in the calculation of its free energy surface [Nature, 2014, 510, 385; J. Chem. Phys., 2013, 138, 214504]. Current evidence supporting or not supporting the LLPT is mostly derived from the thermodynamic stability of the LDL phase. Provided that the HDL-LDL transition is a first-order transition, the formation of LDL silicon should be an activated process. Following this idea, the nature of the LLPT should be clarified by tracing the kinetic path toward LDL silicon. In this work, we focus on the transformation process from HDL to LDL phases and use the mean first passage time (MFPT) method to examine thermodynamic and dynamic trajectories. The MFPT results show that the presumed HDL-LDL transition is not characterized by a thermodynamic activated process but by a continuous dynamic transformation. LDL silicon is actually a mixture of the high-density liquid and a low-density tetrahedral network. We show that the five-membered Si-Si rings in the LDL network play a critical role in stabilizing the low-density network and suppressing the crystallization.

Role of string-like collective atomic motion on diffusion and structural relaxation in glass forming Cu-Zr alloys.

We investigate Cu-Zr liquid alloys using molecular dynamics simulation and well-accepted embedded atom method potentials over a wide range of chemical composition and temperature as model metallic glass-forming (GF) liquids. As with other types of GF materials, the dynamics of these complex liquids are characterized by "dynamic heterogeneity" in the form of transient polymeric clusters of highly mobile atoms that are composed in turn of atomic clusters exhibiting string-like cooperative motion. In accordance with the string model of relaxation, an extension of the Adam-Gibbs (AG) model, changes in the activation free energy ΔGa with temperature of both the Cu and Zr diffusion coefficients D, and the alpha structural relaxation time τα can be described to a good approximation by changes in the average string length, L. In particular, we confirm that the strings are a concrete realization of the abstract "cooperatively rearranging regions" of AG. We also find coexisting clusters of relatively "immobile" atoms that exhibit predominantly icosahedral local packing rather than the low symmetry packing of "mobile" atoms. These two distinct types of dynamic heterogeneity are then associated with different fluid structural states. Glass-forming liquids are thus analogous to polycrystalline materials where the icosahedrally packed regions correspond to crystal grains, and the strings reside in the relatively disordered grain boundary-like regions exterior to these locally well-ordered regions. A dynamic equilibrium between localized ("immobile") and wandering ("mobile") particles exists in the liquid so that the dynamic heterogeneity can be considered to be type of self-assembly process. We also characterize changes in the local atomic free volume in the course of string-like atomic motion to better understand the initiation and propagation of these fluid excitations.

Anomalous temperature dependence of elastic limit in metallic glasses.

Understanding the atomistic mechanisms of inelastic deformation in metallic glasses (MGs) remains challenging due to their amorphous structure, where local carriers of plasticity cannot be easily defined. Using molecular dynamics (MD) simulations, we analyzed the onset of inelastic deformation in CuZr MGs, specifically the temperature dependence of the elastic limit, in terms of localized shear transformation (ST) events. We find that although the ST events initiate at lower strain with increasing temperature, the elastic limit increases with temperature in certain temperature ranges. We explain this anomalous behavior through the framework of an energy-strain landscape (ESL) constructed from high-throughput strain-dependent energy barrier calculations for the ST events identified in the MD simulations. The ESL reveals that the anomalous behavior is caused by the transition of ST events from irreversible to reversible with increasing temperature. An analytical formulation is developed to predict this transition and the temperature dependence of the elastic limit.

Alkali-Ion Batteries by Carbon Encapsulation of Liquid Metal Anode.

Gallium-based metallic liquids, exhibiting high theoretical capacity, are considered a promising anode material for room-temperature liquid metal alkali-ion batteries. However, electrochemical performances, especially the cyclic stability, of the liquid metal anode for alkali-ion batteries are strongly limited because of the volume expansion and unstable solid electrolyte interphase film of liquid metal. Here, the bottleneck problem is resolved by designing carbon encapsulation on gallium-indium liquid metal nanoparticles (EGaIn@C LMNPs). A superior cycling stability (644 mAh g-1 after 800 cycles at 1.0 A g-1 ) is demonstrated for lithium-ion batteries, and excellent cycle stability (87 mAh g-1 after 2500 cycles at 1.0 A g-1 ) is achieved for sodium-ion batteries by carbon encapsulation of the liquid metal anode. Morphological and phase changes of EGaIn@C LMNPs during the electrochemical reaction process are revealed by in situ transmission electron microscopy measurements in real-time. The origin for the excellent performance is uncovered, that is the EGaIn@C core-shell structure effectively suppresses the non-uniform volume expansion of LMNPs from ≈160% to 127%, improves the electrical conductivity of the LMNPs, and exhibits superior electrochemical kinetics and a self-healing phenomenon. This work paves the way for the applications of room-temperature liquid metal anodes for high-performance alkali-ion batteries.

Plasticity Improvement in a Co-Rich Co40Fe25Cr20Ni15 High-Entropy Alloy via Al Alloying.

The mechanical properties of high-entropy alloys (HEAs) can be regulated by altering the stacking fault energy (SFE) through compositional modulation. The Co-rich HEAs, exhibiting deformation twinning and even strain-induced martensitic transformation at room temperature, suffer from insufficient ductility at high strength. In this work, we developed Co-rich (Co40Fe25Cr20Ni15)100-xAlx (x = 0 and 5 at.%) HEAs and investigated their tensile behaviors at room temperature. The addition of Al resulted in a massive improvement in the strength-ductility product, even at similar grain sizes, and also altered the fracture mode from quasi-cleavage to ductile dimple fracture. Interestingly, both alloys were deformed by mechanical twinning, which was also verified by molecular dynamics (MD) simulations. The MD simulations revealed the SFE increased upon Al addition; however, the slip energy barrier was reduced, which favored the mobility of dislocations and twinning propensity to prolong strain hardening. The present findings provide further insights into the regulation of mechanical properties of HEAs by Al-alloying.

Substitutional alloy of Ce and Al.

The formation of substitutional alloys has been restricted to elements with similar atomic radii and electronegativity. Using high-pressure at 298 K, we synthesized a face-centered cubic disordered alloy of highly dissimilar elements (large Ce and small Al atoms) by compressing the Ce(3)Al intermetallic compound >15 GPa or the Ce(3)Al metallic glass >25 GPa. Synchrotron X-ray diffraction, Ce L(3)-edge absorption spectroscopy, and ab initio calculations revealed that the pressure-induced Kondo volume collapse and 4f electron delocalization of Ce reduced the differences between Ce and Al and brought them within the Hume-Rothery (HR) limit for substitutional alloying. The alloy remained after complete release of pressure, which was also accompanied by the transformation of Ce back to its ambient 4f electron localized state and reversal of the Kondo volume collapse, resulting in a non-HR alloy at ambient conditions.

Temperature and chemical effects on the interfacial energy between a Ga-In-Sn eutectic liquid alloy and nanoscopic asperities.

The interfacial energies between a eutectic Ga-In-Sn liquid alloy and single nanoscopic asperities of SiO x , Au, and PtSi have been determined in the temperature range between room temperature and 90 °C by atomic force spectroscopy. For all asperities used here, we find that the interfacial tension of the eutectic Ga-In-Sn liquid alloy is smaller than its free surface energy by a factor of two (for SiO x ) to eight (for PtSi). Any significant oxide growth upon heating studied was not detected here, and the measured interfacial energies strongly depend on the chemistry of the asperities. We also observe a weak increase of the interfacial energy as a function of the temperature, which can be explained by the reactivity between SiO x and Ga and the occurrence of chemical segregation at the liquid alloy surface.

Soft and Stretchable Liquid Metal-Elastomer Composite for Wearable Electronics.

Soft devices, especially capacitive stress (or strain) sensors, are important for applications, including wearable medical monitoring, electronic skin, and soft robotics. The incorporation of liquid metal particles (LMPs) into highly deformable elastomers as inclusions ameliorates the mechanical compliance caused by a rigid filler. The high dielectric constant and liquid feature of LMPs are suitable for soft sensors with high sensitivity and a large real-time dynamic detection range. Here, a class of LM-elastomer composites are introduced with elastic and high dielectric properties, making them uniquely suitable for the application of soft stress sensors. The prepared stretchable soft stress sensor can detect the bending degree of the finger, monitor physiological signals in real time, and distinguish the vibration from the pronunciation of different letters. The nanoscale X-ray computational tomography (nano-CT) measurements indeed detect the changes of LMPs under stress, i.e., LMPs in the matrix distribute from uneven to relatively uniform, agglomerate, and even connect each other to have a conduction path in the composition with high LMP contents, which cause the changes in the physical properties of devices under operation. The cognition of LMP changes in composites under stress is instructive for promoting their further applications in the field of soft devices.

Extra plasticity governed by shear band deflection in gradient metallic glasses.

Inspired by gradient materials in nature, advanced engineering components with controlled structural gradients have attracted substantial research interests due to their exceptional combinations of properties. However, it remains challenging to generate structural gradients that penetrate through bulk materials, which is essential for achieving enhanced mechanical properties in metallic materials. Here, we report practical strategies to design controllable structural gradients in bulk metallic glasses (BMGs). By adjusting processing conditions, including holding time and/or controlling temperatures, of cryogenic thermal cycling and fast cooling, two different types of gradient metallic glasses (GMGs) with spatially gradient-distributed free volume contents can be synthesized. Both mechanical testing and atomistic simulations demonstrate that the spatial gradient can endow GMGs with extra plasticity. Such an enhanced mechanical property is governed by the gradient-induced deflection of shear deformation that fundamentally suppresses the unlimited shear localization on a straight plane that would be expected in BMGs without such a gradient.

Production of Uniformly Sized Gallium-Based Liquid Alloy Nanodroplets via Ultrasonic Method and Their Li-Ion Storage.

Gallium-based liquid alloys are attractive due to their unique properties, and they can potentially be applied in the field of flexible electronics as coolant materials for nuclear and liquid batteries, due to the high thermal conductivity and excellent fluid properties of liquid metals. However, it is still challenging to fabricate gallium-based liquid alloy nanodroplets with uniform and small size. Here, we performed a systematical study on the influence of various factors affecting the size of nanodroplets. Liquid metal nanodroplets with an average size of 74 nm and narrow size distribution were successfully fabricated. Li-ion half-cells were assembled with eutectic GaIn (eGaIn) nanodroplets as anode active materials, which showed higher specific capacity than the bulk eGaIn alloy under the same testing conditions.

ß-Relaxation and Crystallization Behaviors in a Pulse-Current-Thermoplastic-Formed La-Based Bulk Metallic Glass.

We use the pulse current thermoplastic forming technique based on joule heating to rejuvenate the atomic structure of a La62Al14Ag2.34Ni10.83Co10.83 bulk metallic glass (BMG). The pulse-formed sample exhibits more pronounced ß-relaxation than the as-cast one due to the increased free volume. Instead, the sub-Tg annealing clearly weakens the ß-relaxation and also makes it more isolated from the α-relaxation, showing contributions from free volume and preferred structure. However, both treatments exhibit little influence on the following α-relaxation and high temperature crystallization kinetics. Our results open an effective way to rejuvenate the structure of BMGs and provide an in-depth understanding of the relationship between structural relaxations and crystallization kinetics of BMGs.

A dual-phase alloy with ultrahigh strength-ductility synergy over a wide temperature range.

High-entropy alloys (HEAs), as an emerging class of materials, have pointed a pathway in developing alloys with interesting property combinations. Although they are not exempted from the strength-ductility trade-off, they present a standing chance in overcoming this challenge. Here, we report results for a precipitation-strengthening strategy, by tuning composition to design a CoNiV-based face-centered cubic/B2 duplex HEA. This alloy sustains ultrahigh gigapascal-level tensile yield strengths and excellent ductility from cryogenic to elevated temperatures. The highest specific yield strength (~150.2 MPa·cm3/g) among reported ductile HEAs is obtained. The ability of the alloy presented here to sustain this excellent strength-ductility synergy over a wide temperature range is aided by multiple deformation mechanisms i.e., twins, stacking faults, dynamic strain aging, and dynamic recrystallization. Our results open the avenue for designing precipitation-strengthened lightweight HEAs with advanced strength-ductility combinations over a wide service temperature range.

Palladium nanoparticles anchored on amphiphilic Janus-type cellulose nanocrystals for Pickering interfacial catalysis.

Developing green and sustainable Pickering interfacial catalysts for organic reactions in water is of great importance to both the environment and human health. In this study, Janus-type amphiphilic cellulose nanocrystals (CNCs) were synthesized by the surface modification of hydrophilic CNCs with hydrophobic alkyl chains for efficient Pickering emulsion stabilization. Further deposition of palladium nanoparticles on amphiphilic CNCs provides catalytic activity for organic reactions in water, which occur at the interface of water and the organic reactant phase. Different reactions, hydrogenation and C-C coupling, were performed using the obtained Pickering interfacial catalyst. Excellent results were achieved in both reactions. The catalyst developed in our study is expected to advance the field of environment-friendly catalyst systems for green chemistry.