A discrete spectral analysis for determining quasi-linear viscoelastic properties of biological materials

The viscoelastic behaviour of a biological material is central to its functioning and is an indicator of its health. The Fung quasi-linear viscoelastic (QLV) model, a standard tool for characterizing biological materials, provides excellent fits to most stress–relaxation data by imposing a simple form upon a material''s temporal relaxation spectrum. However, model identification is challenging because the Fung QLV model''s ‘box’-shaped relaxation spectrum, predominant in biomechanics applications, can provide an excellent fit even when it is not a reasonable representation of a material''s relaxation spectrum. Here, we present a robust and simple discrete approach for identifying a material''s temporal relaxation spectrum from stress–relaxation data in an unbiased way. Our ‘discrete QLV’ (DQLV) approach identifies ranges of time constants over which the Fung QLV model''s typical box spectrum provides an accurate representation of a particular material''s temporal relaxation spectrum, and is effective at providing a fit to this model. The DQLV spectrum also reveals when other forms or discrete time constants are more suitable than a box spectrum. After validating the approach against idealized and noisy data, we applied the methods to analyse medial collateral ligament stress–relaxation data and identify the strengths and weaknesses of an optimal Fung QLV fit.     

Cluster‐Assembled Nanocomposites: Functional Properties by Design

The unique functional properties of nanocomposites meet many of the material requirements sought after in numerous applications of today's high‐tech industry. This, in turn, inspires material scientists to devise new methods that can further expand the palette of available nanocomposites. Precise control over the chemistry, morphology, and microstructure of nanocomposites' constituents promises the eventual ability to design any composite material for any specific requirement. However, today's synthesis methods still lack the ability to simultaneously control all chemical, morphological, and microstructural features of nanocomposites in a one‐step process. Here, an alternative approach to fabricate fully tailorable nanocomposites under well‐defined conditions is described. In particular, this progress report focuses on the combination of cluster ion beam and thin‐film deposition technologies to fabricate cluster‐assembled nanocomposites via codeposition of cluster ions and matrix materials. Emphasis is given to the state‐of‐the‐art cluster deposition system, designed and built by our research group, as well as to its unique abilities. Moreover, case studies on two cluster‐assembled nanocomposite material systems (Fe/Ag_m and Fe/Cr_m) prepared with this method are presented. Finally, an outlook on research directions for cluster‐assembled nanocomposites is discussed.     

Direct Imaging of Dopant and Impurity Distributions in 2D MoS2

Molybdenum disulfide (MoS₂) nanosheet is a two-dimensional (2D) material with high electron mobility and with high potential for applications in catalysis and electronics. MoS₂ nanosheets are synthesized using a one-pot wet-chemical synthesis route with and without Re doping. Atom probe tomography reveals that 3.8 at% Re is homogeneously distributed within the Re-doped sheets. Other impurities are also found integrated within the material: light elements including C, N, O, and Na, locally enriched up to 0.1 at%, as well as heavy elements such as V and W. Analysis of the nondoped sample reveals that the W and V likely originate from the Mo precursor. It is shown how wet-chemical synthesis results in an uncontrolled integration of species from the solution that can affect the material's activity. The results of this work are expected to contribute to an improved understanding of the relationships linking composition to properties of 2D transition-metal dichalcogenide materials.     

Efficient Mercury Capture Using Functionalized Porous Organic Polymer

The primary challenge in materials design and synthesis is achieving the balance between performance and economy for real‐world application. This issue is addressed by creating a thiol functionalized porous organic polymer (POP) using simple free radical polymerization techniques to prepare a cost‐effective material with a high density of chelating sites designed for mercury capture and therefore environmental remediation. The resulting POP is able to remove aqueous and airborne mercury with uptake capacities of 1216 and 630 mg g^?1, respectively. The material demonstrates rapid kinetics, capable of dropping the mercury concentration from 5 ppm to 1 ppb, lower than the US Environmental Protection Agency's drinking water limit (2 ppb), within 10 min. Furthermore, the material has the added benefits of recyclability, stability in a broad pH range, and selectivity for toxic metals. These results are attributed to the material's physical properties, which include hierarchical porosity, a high density of chelating sites, and the material's robustness, which improve the thiol availability to bind with mercury as determined by X‐ray photoelectron spectroscopy and X‐ray absorption fine structure studies. The work provides promising results for POPs as an economical material for multiple environmental remediation applications.     

Dopant Segregation Boosting High‐Voltage Cyclability of Layered Cathode for Sodium Ion Batteries

As a widely used approach to modify a material's bulk properties, doping can effectively improve electrochemical properties and structural stability of various cathodes for rechargeable batteries, which usually empirically favors a uniform distribution of dopants. It is reported that dopant aggregation effectively boosts the cyclability of a Mg‐doped P2‐type layered cathode (Na_0.67Ni_0.33Mn_0.67O₂). Experimental characterization and calculation consistently reveal that randomly distributed Mg dopants tend to segregate into the Na‐layer during high‐voltage cycling, leading to the formation of high‐density precipitates. Intriguingly, such Mg‐enriched precipitates, acting as 3D network pillars, can further enhance a material's mechanical strength, suppress cracking, and consequently benefit cyclability. This work not only deepens the understanding on dopant evolution but also offers a conceptually new approach by utilizing precipitation strengthening design to counter cracking related degradation and improve high‐voltage cyclability of layered cathodes.     

Shape‐Controlled Synthesis of High‐Quality Cu7S4 Nanocrystals for Efficient Light‐Induced Water Evaporation

Copper sulfides (Cu_2–xS), are a novel kind of photothermal material exhibiting significant photothermal conversion efficiency, making them very attractive in various energy conversion related devices. Preparing high quality uniform Cu_2‐xS nanocrystals (NCs) is a top priority for further energy‐and sustainability relevant nanodevices. Here, a shape‐controlled high quality Cu₇S₄ NCs synthesis strategy is reported using sulfur in 1‐octadecene as precursor by varying the heating temperature, as well as its forming mechanism. The performance of the Cu₇S₄ NCs is further explored for light‐driven water evaporation without the need of heating the bulk liquid to the boiling point, and the results suggest that as‐synthesized highly monodisperse NCs perform higher evaporation rate than polydisperse NCs under the identical morphology. Furthermore, disk‐like NCs exhibit higher water evaporation rate than spherical NCs. The water evaporation rate can be further enhanced by assembling the organic phase Cu₇S₄ NCs into a dense film on the aqueous solution surface. The maximum photothermal conversion efficiency is as high as 77.1%.     

Postsynthetic Doping of MnCl2 Molecules into Preformed CsPbBr3 Perovskite Nanocrystals via a Halide Exchange‐Driven Cation Exchange

Unlike widely used postsynthetic halide exchange for CsPbX₃ (X is halide) perovskite nanocrystals (NCs), cation exchange of Pb is of a great challenge due to the rigid nature of the Pb cationic sublattice. Actually, cation exchange has more potential for rendering NCs with peculiar properties. Herein, a novel halide exchange‐driven cation exchange (HEDCE) strategy is developed to prepare dually emitting Mn‐doped CsPb(Cl/Br)₃ NCs via postsynthetic replacement of partial Pb in preformed perovskite NCs. The basic idea for HEDCE is that the partial cation exchange of Pb by Mn has a large probability to occur as a concomitant result for opening the rigid halide octahedron structure around Pb during halide exchange. Compared to traditional ionic exchange, HEDCE is featured by proceeding of halide exchange and cation exchange at the same time and lattice site. The time and space requirements make only MnCl₂ molecules (rather than mixture of Mn and Cl ions) capable of doping into perovskite NCs. This special molecular doping nature results in a series of unusual phenomenon, including long reaction time, core–shell structured mid states with triple emission bands, and dopant molecules composition‐dependent doping process. As‐prepared dual‐emitting Mn‐doped CsPb(Cl/Br)₃ NCs are available for ratiometric temperature sensing.     

Theoretical framework for estimating a product's reliability using a variable‐amplitude loading spectrum and a stress‐based approach

An innovative approach for predicting the reliability of a structure that is subject to a variable‐amplitude dynamic load is presented. In this approach, a Gassner durability curve with its scatter is modelled using a 2‐parametric Weibull's probability density function (PDF). The trend of the Gassner durability curve is modelled with a general hyperbola equation in a log‐log scale. The hyperbola equation is applied to represent the durability curve for the 63.2% probability of fatigue failure that describes the dependency of the Weibull's scale parameter on the loading spectrum's maximum stress. Equations are derived to link the parameters of the hyperbola curve to the material's S‐N curve and the loading spectrum. The Weibull's shape parameter is estimated from the scatter of the material's S‐N curve. The proposed Gassner‐curve model is applied to calculate the fatigue reliability from the PDF of the loading spectrum's maximum stress and the PDF of the durability‐curve's amplitude stress for the selected number of loading‐cycles‐to‐failure.     

Improving the Quality and Luminescence Performance of All‐Inorganic Perovskite Nanomaterials for Light‐Emitting Devices by Surface Engineering

Lead halide perovskites and their applications in the optoelectronic field have garnered intensive interest over the years. Inorganic perovskites (IHP), though a novel class of material, are considered as one of the most promising optoelectronic materials. These materials are widely used in detectors, solar cells, and other devices, owing to their excellent charge‐transport properties, high defect tolerance, composition‐ and size‐dependent luminescence, narrow emission, and high photoluminescence quantum yield. In recent years, numerous encouraging achievements have been realized, especially in the research of CsPbX₃ (X = Cl, Br, I) nanocrystals (NCs) and surface engineering. Therefore, it is necessary to summarize the principles and effects of these surface engineering optimization methods. It is also important to scientifically guide the applications and promote the development of perovskites more efficiently. Herein, the principles of surface ligands are reviewed, and various surface treatment methods used in CsPbX₃ NCs as well as quantum‐dot light‐emitting diodes are presented. Finally, a brief outlook on CsPbX₃ NC surface engineering is offered, illustrating the present challenges and the direction in which future investigations are intended to obtain high‐quality CsPbX₃ NCs that can be utilized in more applications.     

Electrical contacts for FeSi2 and higher manganese silicide thermoelectric elements

A furnace was constructed to solder thermoelectric materials at high temperatures in vacuum or a gas atmosphere. Electrical junctions for the hot side of a thermoelectric generator consisting of FeSi₂ and higher manganese suicide were developed. Material for the junction is TiSi₂ soldered with ‘Ti-activated’ Ag. Contact resistivity was found to be low compared to the material's resistances and stable against the thermal stress at the working temperature. Electron microscopic investigations did not detect any ageing process. The results support the applicability of the developed contacts in a thermoelectric generator.     

Rapid preparation of spinel Co3O4 nanocrystals in aqueous phase by microwave irradiation

In this paper, we present a new method for synthesis of water-soluble Co₃O₄ nanocrystals (NCs) by microwave irradiation with controllable temperature. Spherical or cubic Co₃O₄ NCs (10–20 nm) were synthesized rapidly within 10 min at 100–140 °C. MPA was used as stabilizer to synthesis Co₃O₄ NCs in this paper, which leads to the controlled growth and narrow sizes distribution of the NCs. Our results demonstrated that the shape of Co₃O₄ NCs was reaction temperature-dependent, i.e., low temperature is in favor of the synthesis of spherical NCs, and high temperature is in that of cubic NCs.     

Colloidal synthesis of ultrathin two-dimensional semiconductor nanocrystals

2D semiconductor quantum wells have been recognized as potential candidates for various quantum devices. In quantum wells, electrons and holes are spatially confined within a finite thickness and freely move in 2D space. Much effort has focused on shape control of colloidal semiconductor nanocrystals(NCs), and synthesis of 2D colloidal NCs has been achieved very recently. Here, recent advances in colloidal synthesis of uniform and ultrathin 2D CdSeNCs are highlighted. Structural and optical property characterization of these quantum-sized 2D CdSe NCs is discussed. Additionally, 2D CdSe NCs doped with Mn 2+ ions for dilute magnetic semiconductors (DMS) are presented.These 2D CdSe-based NCs can be used as model systems for studying quantum-well structures.     

Ultrasonic Assisted Fabrication of Nanocomposite Electrode Materials Au/C for Low-Voltage Electronics

Au/C nanocomposites have been obtained by the ultrasonic assisted reduction of HAuCl₄ solutions, impregnated in carbon material pores, using NaBH₄ as a reducing agent. It was established that conditions of nanocomposite (NC) synthesis exert an essential influence on the shape and size characteristics of Au filler and functional properties of NCs. Characterization of NCs by X-ray diffraction, small-angle X-ray scattering, and cyclic voltammetry methods has revealed that an increase in the NaBH₄ concentration raises not only gold nanoparticle dispersion in composites but also an electrochemical capacitance of Au/C NC electrode materials. A higher specific capacitance (700 F/g) for the NC electrode (NC-5 wt%-Au/C-1) was observed at a scanning rate of 10 mV/s in the potential window from (?1)V to (+1)V.     

Synthesis of Thermally Stable and Highly Luminescent Cs5Cu3Cl6I2 Nanocrystals with Nonlinear Optical Response

Low-dimensional Cu(I)-based metal halide materials are gaining attention due to their low toxicity, high stability and unique luminescence mechanism, which is mediated by self-trapped excitons (STEs). Among them, Cs₅Cu₃Cl₆I₂, which emits blue light, is a promising candidate for applications as a next-generation blue-emitting material. In this article, an optimized colloidal process to synthesize uniform Cs₅Cu₃Cl₆I₂ nanocrystals (NCs) with a superior quantum yield (QY) is proposed. In addition, precise control of the synthesis parameters, enabling anisotropic growth and emission wavelength shifting is demonstrated. The synthesized Cs₅Cu₃Cl₆I₂ NCs have an excellent photoluminescence (PL) retention rate, even at high temperature, and exhibit high stability over multiple heating–cooling cycles under ambient conditions. Moreover, under 850-nm femtosecond laser irradiation, the NCs exhibit three-photon absorption (3PA)-induced PL, highlighting the possibility of utilizing their nonlinear optical properties. Such thermally stable and highly luminescent Cs₅Cu₃Cl₆I₂ NCs with nonlinear optical properties overcome the limitations of conventional blue-emitting nanomaterials. These findings provide insights into the mechanism of the colloidal synthesis of Cs₅Cu₃Cl₆I₂ NCs and a foundation for further research.     

High Density Single Fe Atoms on Mesoporous N-Doped Carbons: Noble Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Acidic and Alkaline Media

It remains a challenge to develop efficient noble metal-free electrocatalysts for the oxygen reduction reaction (ORR) in various renewable energy systems. Single atom catalysts have recently drawn great attention as promising candidates both due to their high activity and their utmost atom utilization for electrocatalytic ORR. Herein, the synthesis of an efficient ORR electrocatalyst that is composed of N-doped mesoporous carbon and a high density (4.05 wt%) of single Fe atoms via pyrolysis Fe-conjugated polymer is reported. Benefiting from the abundant atomic Fe–N₄ sites on its conductive, mesoporous carbon structures, this material exhibits an excellent electrocatalytic activity for ORR, with positive onset potentials of 0.93 and 0.98 V in acidic and alkaline media, respectively. Its electrocatalytic performance for ORR is also comparable to that of Pt/C (20 wt%) in both media. Furthermore, it electrocatalyzes the reaction almost fully to H₂O (or barely to H₂O₂). Additionally, it is durable and tolerates the methanol crossover reaction well. Furthermore, a proton exchange membrane fuel cell and a zinc–air battery assembled using it on their cathode deliver high maximum power densities (320 and 91 mW cm⁻², respectively). Density functional theory calculation reveals that the material's decent electrocatalytic performance for ORR is due to its atomically dispersed Fe–N₄ sites.     

An Amorphous/Crystalline Incorporated Si/SiOx Anode Material Derived from Biomass Corn Leaves for Lithium‐Ion Batteries

The fabrication of silicon (Si) anode materials derived from high silica‐containing plants enables effective utilization of subsidiary agricultural products. However, the electrochemical performances of synthesized Si materials still require improvement and thus need further structural design and morphology modifications, which inevitably increase preparation time and economic cost. Here, the conversion of corn leaves into Si anode materials is reported via a simple aluminothermic reduction reaction without other modifications. The obtained Si material inherits the structural characteristics of the natural corn leaf template and has many inherent advantages, such as high porosity, amorphous/crystalline mixture structure, and high‐valence SiO_x residuals, which significantly enhance the material's structural stability and electrode adhesive strength, resulting in superior electrochemical performances. Rate capability tests show that the material delivers a high capacity of 1200 mA h g^?1 at 8 A g^?1 current density. After 300 cycles at 0.5 A g^?1, the material maintains a high specific capacity of 2100 mA h g^?1, with nearly 100% capacity retention during long‐term cycling. This study provides an economical route for the industrial production of Si anode materials for Lithium‐Ion batteries.     

Highly Emissive Green Perovskite Nanocrystals in a Solid State Crystalline Matrix

Perovskite nanocrystals (NCs) have attracted attention due to their high photoluminescence quantum yield (PLQY) in solution; however, maintaining high emission efficiency in the solid state remains a challenge. This study presents a solution‐phase synthesis of efficient green‐emitting perovskite NCs (CsPbBr₃) embedded in robust and air‐stable rhombic prism hexabromide (Cs₄PbBr₆) microcrystals, reaching a PLQY of 90%. Theoretical modeling and experimental characterization suggest that lattice matching between the NCs and the matrix contribute to improved passivation, while spatial confinement enhances the radiative rate of the NCs. In addition, dispersing the NCs in a matrix prevents agglomeration, which explains their high PLQY.     

Time-dependent fracture of type 316L(N) steel at ambient temperature

Experimental data on tensile and compact geometry (CT) specimens of austenitic Type 316L(N) steel were obtained under sustained load conditions at room temperature. Time‐dependent crack growth, in some cases leading to failure, occurred in many of the CT specimens, dependent on the load level. However, rupture of the uniaxial specimens occurred only at stresses very close to the material's ultimate strength. The data validate the approach to assessing sustained loading effects in the R6 defect assessment procedure. In particular, sustained load effects in austenitic steel may be neglected for values of the R6 L_r parameter less than unity. Uniaxial sustained load tests were also performed at 100 °C and 200 °C. The measured strain rates decreased with increasing temperature, becoming negligible at 200 °C. This is consistent with the advice in R6 that sustained load effects in austenitic steel can be neglected at temperatures between 200 °C and the high‐temperature creep range.     

One-pot route for preparation of monodisperse CuInS2 nanocrystals

Chalcopyrite copper indium sulfide (CuInS₂) nanocrystals (NCs) were synthesized by a one-pot route and characterized by XRD, TEM, HRTEM, EDS, UV-vis and SPS. The experimental results demonstrated that the CuInS₂ NCs synthesized by metal compound [Sn(acac)₂Cl₂] had good crystallinity, monodispersity and stoichiometric composition. The UV-vis absorption spectra showed the as-synthesized CuInS₂ NCs had fine absorption in the visible light region and the energy band gap was estimated to be 1.58 eV. Moreover, the metal compound could improve the photoinduced charge separation and transfer effect of NCs based on the SPS study. The synthesis strategy developed in this work may be used as a general process for the synthesis of pure or doped chalcogenide NCs, and may have great potential to be applied in high efficiency, yet low cost photovoltaic areas.     

Manganese Doped Fluorescent Paramagnetic Nanocrystals for Dual‐Modal Imaging

In this work, dual‐modal (fluorescence and magnetic resonance) imaging capabilities of water‐soluble, low‐toxicity, monodisperse Mn‐doped ZnSe nanocrystals (NCs) with a size (6.5 nm) below the optimum kidney cutoff limit (10 nm) are reported. Synthesizing Mn‐doped ZnSe NCs with varying Mn²⁺ concentrations, a systematic investigation of the optical properties of these NCs by using photoluminescence (PL) and time resolved fluorescence are demonstrated. The elemental properties of these NCs using X‐ray photoelectron spectroscopy and inductive coupled plasma‐mass spectroscopy confirming Mn²⁺ doping is confined to the core of these NCs are also presented. It is observed that with increasing Mn²⁺ concentration the PL intensity first increases, reaching a maximum at Mn²⁺ concentration of 3.2 at% (achieving a PL quantum yield (QY) of 37%), after which it starts to decrease. Here, this high‐efficiency sample is demonstrated for applications in dual‐modal imaging. These NCs are further made water‐soluble by ligand exchange using 3‐mercaptopropionic acid, preserving their PL QY as high as 18%. At the same time, these NCs exhibit high relaxivity (≈2.95 mM^?1 s^?1) to obtain MR contrast at 25 °C, 3 T. Therefore, the Mn²⁺ doping in these water‐soluble Cd‐free NCs are sufficient to produce contrast for both fluorescence and magnetic resonance imaging techniques.