Metastable 1T'-phase group VIB transition metal dichalcogenide crystals.

Metastable 1T'-phase transition metal dichalcogenides (1T'-TMDs) with semi-metallic natures have attracted increasing interest owing to their uniquely distorted structures and fascinating phase-dependent physicochemical properties. However, the synthesis of high-quality metastable 1T'-TMD crystals, especially for the group VIB TMDs, remains a challenge. Here, we report a general synthetic method for the large-scale preparation of metastable 1T'-phase group VIB TMDs, including WS2, WSe2, MoS2, MoSe2, WS2xSe2(1-x) and MoS2xSe2(1-x). We solve the crystal structures of 1T'-WS2, -WSe2, -MoS2 and -MoSe2 with single-crystal X-ray diffraction. The as-prepared 1T'-WS2 exhibits thickness-dependent intrinsic superconductivity, showing critical transition temperatures of 8.6 K for the thickness of 90.1 nm and 5.7 K for the single layer, which we attribute to the high intrinsic carrier concentration and the semi-metallic nature of 1T'-WS2. This synthesis method will allow a more systematic investigation of the intrinsic properties of metastable TMDs.

Mechanochemically Processed Nd-Fe-Co-Cr-B Nanoparticles with High Coercivity and Reduced Spin Reorientation Transition Temperature.

Nd-Fe-B magnets, possessing the highest energy product, are extensively used in cutting-edge applications, including electrical machines and electrical vehicles. An environmentally benign and cost effective synthesis method of Cr alloyed Nd2 (Fe,Co)14 B magnetic nanoparticles using a dry mechanochemical process is reported. The method is solvent free, facile, energy efficient and scalable. The reduction of mixed oxides of Nd, Fe, Co, B and Cr is performed by using Ca. The coercivity (HC ) of the nanoparticles is found to depend on the dispersant content, with the highest value obtained for Nd2 (Fe11.25 Co2 Cr0.75 )B with 40 % CaO dispersant. The HC of isolated Nd2 (Fe11.25 Co2 Cr0.75 )B nanoparticles and nanoparticles embedded in a CaO matrix is found to be 11.5 kOe and 14.4 kOe, respectively, largest values for heavy rare earth free Nd-Fe-B nanoparticles with reasonable saturation and remanent magnetization, regardless of synthesis route. Considering the density of Nd2 Fe14 B, an energy product of 14.2 MGOe is obtained for the nanoparticles. The thermal coefficient of remanence and thermal coefficient of coercivity for aligned samples are -0.06 % and -0.29 %, respectively, in the temperature range between 100 K and 400 K. The spin reorientation temperature is found to be ∼30 K less than that of bulk Nd2 Fe14 B magnets.

Hot exciton cooling and multiple exciton generation in PbSe quantum dots.

Multiple exciton generation (MEG) is a promising process to improve the power conversion efficiency of solar cells. PbSe quantum dots (QDs) have shown reasonably high MEG quantum yield (QY), although the photon energy threshold for this process is still under debate. One of the reasons for this inconsistency is the complicated competition of MEG and hot exciton cooling, especially at higher excited states. Here, we investigate MEG QY and the origin of the photon energy threshold for MEG in PbSe QDs of three different sizes by studying the transient absorption (TA) spectra, both at the band gap (near infrared, NIR) and far from the band gap energy (visible range). The comparison of visible TA spectra and dynamics for different pump wavelengths, below, around and above the MEG threshold, provides evidence of the role of the Σ transition in slowing down the exciton cooling process that can help MEG to take over the phonon relaxation process. The universality of this behavior is confirmed by studying QDs of three different sizes. Moreover, our results suggest that MEG QY can be determined by pump-probe experiments probed above the band gap.

Towards perfectly ordered novel ZnO/Si nano-heterojunction arrays.

The fabrication of a highly ordered novel ZnO/Si nano-heterojuntion array is introduced. ZnO seed layer is first deposited on the Si (P<111>) surface. The nucleation sites are then defined by patterning the surface through focused ion beam (FIB) system. The ZnO nanorods are grown on the nucleation sites through hydrothermal process. The whole fabrication process is simple, facile and offers direct control of the space, length and aspect ratio of the array. It is found that ZnO/Si nanojunctions show an improved interface when subjected to heat treatment. The recrystallization of ZnO and the tensile lattice strain of Si developed during the heating process contribute the enhancement of their photoresponses to white light. The photoluminescence (PL) measurement result of nano-heterojunction arrays with different parameters is discussed.

Experimentally validated inverse design of multi-property Fe-Co-Ni alloys.

This study presents a machine learning (ML) framework aimed at accelerating the discovery of multi-property optimized Fe-Ni-Co alloys, addressing the time-consuming, expensive, and inefficient nature of traditional methods of material discovery, development, and deployment. We compiled a detailed heterogeneous database of the magnetic, electrical, and mechanical properties of Fe-Co-Ni alloys, employing a novel ML-based imputation strategy to address gaps in property data. Leveraging this comprehensive database, we developed predictive ML models using tree-based and neural network approaches for optimizing multiple properties simultaneously. An inverse design strategy, utilizing multi-objective Bayesian optimization (MOBO), enabled the identification of promising alloy compositions. This approach was experimentally validated using high-throughput methodology, highlighting alloys such as Fe66.8Co28Ni5.2 and Fe61.9Co22.8Ni15.3, which demonstrated superior properties. The predicted properties data closely matched experimental data within 14% accuracy. Our approach can be extended to a broad range of materials systems to predict novel materials with an optimized set of properties.

Catechol-functionalized chitosan/iron oxide nanoparticle composite inspired by mussel thread coating and squid beak interfacial chemistry.

Biological materials offer a wide range of multifunctional and structural properties that are currently not achieved in synthetic materials. Herein we report on the synthesis and preparation of bioinspired organic/inorganic composites that mimic the key physicochemical features associated with the mechanical strengthening of both squid beaks and mussel thread coatings using chitosan as an initial template. While chitosan is a well-known biocompatible material, it suffers from key drawbacks that have limited its usage in a wider range of structural biomedical applications. First, its load-bearing capability in hydrated conditions remains poor, and second it completely dissolves at pH < 6, preventing its use in mild acidic microenvironments. In order to overcome these intrinsic limitations, a chitosan-based organic/inorganic biocomposite is prepared that mimics the interfacial chemistry of squid beaks and mussel thread coating. Chitosan was functionalized with catechol moieties in a highly controlled fashion and combined with superparamagnetic iron oxide (γ-Fe2O3) nanoparticles to give composites that represent a significant improvement in functionality of chitosan-based biomaterials. The inorganic/organic (γ-Fe2O3/catechol) interfaces are stabilized and strengthened by coordination bonding, resulting in hybrid composites with improved stability at high temperatures, physiological pH conditions, and acid/base conditions. The inclusion of superparamagnetic particles also makes the composites stimuli-responsive.

High-performance thermomagnetic generator controlled by a magnetocaloric switch.

Low grade waste heat accounts for ~65% of total waste heat, but conventional waste heat recovery technology exhibits low conversion efficiency for low grade waste heat recovery. Hence, we designed a thermomagnetic generator for such applications. Unlike its usual role as the coil core or big magnetic yoke in previous works, here the magnetocaloric material acts as a switch that controls the magnetic circuit. This makes it not only have the advantage of flux reversal of the pretzel-like topology, but also present a simpler design, lower magnetic stray field, and higher performance by using less magnetocaloric material than preceding devices. The effects of key structural and system parameters were studied through a combination of experiments and finite element simulations. The optimized max power density PDmax produced by our device is significantly higher than those of other existing active thermomagnetic, thermo, and pyroelectric generators. Such high performance shows the effectiveness of our topology design of magnetic circuit with magnetocaloric switch.

Highly complex magnetic behavior resulting from hierarchical phase separation in AlCo(Cr)FeNi high-entropy alloys.

Magnetic high-entropy alloys (HEAs) are a new category of high-performance magnetic materials, with multicomponent concentrated compositions and complex multi-phase structures. Although there have been numerous reports of their interesting magnetic properties, there is very limited understanding about the interplay between their hierarchical multi-phase structures and the resulting magnetic behavior. We reveal for the first time the influence of a hierarchically decomposed B2 + A2 structure in an AlCo0.5Cr0.5FeNi HEA on the formation of magnetic vortex states within individual A2 (disordered BCC) precipitates, which are distributed in an ordered B2 matrix that is weakly ferromagnetic. Non-magnetic or weakly ferromagnetic B2 precipitates in large magnetic domains of the A2 phase, and strongly magnetic Fe-Co-rich interphase A2 regions, are also observed. These results provide important insight into the origin of coercivity in this HEA, which can be attributed to a complex magnetization process that includes the successive reversal of magnetic vortices.

Magnetically responsive peptide coacervates for dual hyperthermia and chemotherapy treatments of liver cancer.

Liver cancer is an aggressive malignancy associated with high levels of mortality and morbidity. Doxorubicin (Dox) is often used to slow down liver cancer progression; however its efficacy is limited, and its severe side effects prevent its routine use at therapeutic concentrations. We present a biomimetic peptide that coacervates into micro-droplets, within which both Dox and magnetic nanoparticles (MNPs) can be sequestered. These Dox-loaded Magnetic Coacervates (DMCs) can be used for thermo-chemotherapy, with the controlled release of Dox triggered by an external Alternating Magnetic Field (AMF). The DMCs are internalized by the cells via an energy-independent mechanism which is not based on endocytosis. Application of AMF generates a temperature of 45 °C within the DMCs, triggering their disassembly and the simultaneous release of Dox, thereby resulting in dual hyperthermia and chemotherapy for more efficient cancer therapy. In vitro studies conducted under AMF reveal that DMCs are cytocompatible and effective in inducing HepG2 liver cancer cell death. Thermo-chemotherapy treatment against HepG2 cells is also shown to be more effective compared to either hyperthermia or chemotherapy treatments alone. Thus, our novel peptide DMCs can open avenues in theranostic strategies against liver cancer through programmable, wireless, and remote control of Dox release. STATEMENT OF SIGNIFICANCE: Simultaneous administration of chemical and thermal therapy (thermo-chemotherapy) is more effective in inducing liver cancer cell death and improving survival rate. Thus, there is a keen interest in developing suitable carriers for thermo-chemotherapy. Coacervate micro-droplets display significant advantages, including high loading capacity, fast self-assembly in aqueous environments, and liquid-like behavior. However, they have not yet been explored as carriers for thermo-chemotherapy. Here, we demonstrate that peptide coacervate micro-droplets can co-encapsulate Dox and magnetic nanoparticles and cross the cell membrane. Applying an alternating magnetic field to cells containing drug-loaded coacervates triggers the release of Dox as well as the localized heating by magnetic hyperthermia, resulting in efficient liver cancer cell death by dual thermo-chemotherapy.

Surfactant-directed synthesis of branched bismuth telluride/sulfide core/shell nanorods.

Branched core/shell bismuth telluride/bismuth sulfide nanorod heterostructures are prepared by using a biomimetic surfactant, L-glutathionic acid. Trigonal nanocrystals of bismuth telluride are encapsulated by nanoscopic shells of orthorhombic bismuth sulfide. Crystallographic twinning causes shell branching. Such heteronanostructures are attractive for thermoelectric power generation and cooling applications.

Mechanochemical Synthesis of Iron and Cobalt Magnetic Metal Nanoparticles and Iron/Calcium Oxide and Cobalt/Calcium Oxide Nanocomposites.

We report an environmentally benign and cost-effective method to produce Fe and Co magnetic metal nanoparticles as well as the Fe/Cao and Co/CaO nanocomposites by using a novel, dry mechanochemical process. Mechanochemical milling of metal oxides with a suitable reducing agent resulted in the production of magnetic metal nanoparticles. The process involved grinding and consequent reduction of low-costing oxide powders, unlike conventional processing techniques involving metal salts or metal complexes. Calcium granules were used as the reducing agent. Magnetometry measurements were performed over a large range of temperatures, from 10 to 1273 K, to evaluate the Curie temperature, blocking temperature, irreversibility temperature, saturation magnetization, and coercivity. The saturation magnetizations of the iron and cobalt nanoparticles were found to be 191 and 102 emu g-1, respectively. The heating abilities of these nanoparticles suspended in several liquids under alternating magnetic fields were measured and the specific loss power was determined. Our results suggest that the dry mechanochemical process is a robust method to produce metallic nanoparticles and nanocomposites.

Anisotropic Magnetoelectric Coupling and Cotton-Mouton Effects in the Organic Magnetic Charge-Transfer Complex Pyrene-F4TCNQ.

Magnetoelectric coupling is of high current interest because of its potential applications in multiferroic memory devices. Although magnetoelectric coupling has been widely investigated in inorganic materials, such observations in organic materials are extremely rare. Here, we report our discovery that organic charge-transfer (CT) complex pyrene-2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (pyrene-F4TCNQ) can display anisotropic magnetoelectric coupling. Investigation of the crystal structure of pyrene-F4TCNQ complex demonstrates that the magnetoelectric coupling coefficient along the π-π interaction direction is much larger than the value along other directions. Furthermore, magnetoelectric coupling and magnetization can be tuned by changing the fluorine content in complexes. Besides, the Cotton-Mouton effect in pyrene-F4TCNQ is observed, enabling the control of optomagnetic devices. These results can pave the way for a new method for the future development of organic CT complexes and their applications in perpendicular memory devices and energy-transfer-related multiferroics.

Bioinspired pH and magnetic responsive catechol-functionalized chitosan hydrogels with tunable elastic properties.

We have developed pH- and magnetic-responsive hydrogels that are stabilized by both covalent bonding and catechol/Fe(3+) ligands. The viscoelastic properties of the gels are regulated by the complexation valence and can be used to tune drug release profiles. The stable incorporation of magnetic nanoparticles further expands control over the mechanical response and drug release, in addition to providing magnetic stimuli-responsivity to the gels.

Magnetic nanoparticle-loaded polymer nanospheres as magnetic hyperthermia agents.

Uniform magnetic nanoparticle-loaded polymer nanospheres with different loading contents of manganese ferrite nanoparticles were successfully synthesized using a flexible emulsion process. The MnFe2O4-loaded polymer nanospheres displayed an excellent dispersibility in both water and phosphate buffer saline. The effect of loading ratio and size of MnFe2O4 nanoparticles within the nanospheres on the specific absorption rate (SAR) under an alternating magnetic field was investigated. Our results indicate that a large size (here 18 nm) and a low loading ratio are preferable for a high SAR. For a smaller particle size (6 nm), the low loading ratio did not result in an enhancement of the SAR value, while a very low SAR value is expected for 6 nm. In addition, the SAR of low-content MnFe2O4 (18 nm)-loaded polymer nanospheres in the agarose gel which is simulated for in vivo environment is the highest among the samples and does not change substantially in physiological environments. This differs largely from the behaviour of singly dispersed nanoparticles. Our results have paved the way for the design of MnFe2O4-loaded polymer nanospheres as magnetic hyperthermia agents for in vivo bio-applications.

Morphing soft magnetic composites.

Magnet filler-polymer matrix composites (Magpol) are an emerging class of morphing materials. Applications of Magpol can include artificial muscles, drug delivery, adaptive optics and self healing structures. Advantages of Magpol include remote contactless actuation, several actuation modes, high actuation strain and strain rate, self-sensing and quick response. The actuation modes of Magpol, its dynamic properties, work output and transduction characteristics are described. Analogies between Magpol actuation and phase transformations are presented. As an illustration of Magpol actuation, a proof of concept artificial muscle is presented. Current applications and future prospects are described.