Deep-learning-assisted fiber Bragg grating interrogation by random speckles.

Fiber Bragg gratings (FBGs) have been widely employed as a sensor for temperature, vibration, strain, etc. measurements. However, extant methods for FBG interrogation still face challenges in the aspects of sensitivity, measurement speed, and cost. In this Letter, we introduced random speckles as the FBG's reflection spectrum information carrier for demodulation. Instead of the commonly used InGaAs cameras, a quadrant detector (QD) was first utilized to record the speckle patterns in the experiments. Although the speckle images were severely compressed into four channel signals by the QD, the spectral features of the FBGs can still be precisely extracted with the assistance of a deep convolution neural network (CNN). The temperature and vibration experiments were demonstrated with a resolution of 1.2 pm. These results show that the new, to the best of our knowledge, speckle-based demodulation scheme can satisfy the requirements of both high-resolution and high-speed measurements, which should pave a new way for the optical fiber sensors.

Design of highly efficient g-C3N4-based metal monoatom catalysts by two extra-NM1 atoms: density functional theory simulations.

Graphitic carbon nitride (g-C3N4) is recognized as a favorable substrate for monoatom catalysts due to its uniform nanoholes for anchoring metal monoatoms, while the oxygen evolution reaction (OER) overpotential (ηOER) values of g-C3N4-based metal monoatom catalysts are still large. To reduce the ηOER values, a class of novel TM1NM1NM1/g-C3N4 was designed via density functional theory simulations, where TM1 = Fe1, Co1 or Ni1 and NM1 = C1, N1 or O1. Contributing by two extra-NM1 atoms, the OER catalytic activities of these materials were effectively improved owing to the shortened TM1-NM bonds and weakened chemical activity of TM1 atoms. Based on the volcano activity relationship between the theoretical overpotential (ηOER) and d band center of the TM1 atom (εd), the chemical activity of TM1 atoms needs to be adjusted to a suitable magnitude (εd near -4.883 eV) for a good catalytic activity. The designed Fe1C1O1/g-C3N4 with the εd of -4.893 eV exhibited an excellent OER catalytic activity of ηOER = 0.219 V. This strategy was applied to devise the reaction active sites and highly efficient catalysts by adjusting the chemical activity of the TM1 atom with suitable extra-NM1 atoms.

Wrinkled stripes localized by cracks in metal films deposited on soft substrates.

Homogeneous global wrinkling patterns such as labyrinths, herringbones, ripples and straight stripes can be widely observed in natural and artificial systems, but localized wrinkling patterns (not including buckle-driven delaminations, folds, ridges and creases) are seldom observed in experiments. Here we report on the spontaneous formation of highly ordered wrinkled stripes localized by cracks in metal films deposited on soft substrates. The experiment shows that the metal film is under a large tensile stress during deposition, which is relieved by the formation of networked cracks. After deposition, a compressive stress is stored up in the film and it always focuses near the new formed cracks due to the plastic deformation of the film, resulting in the formation of localized wrinkled stripes composed of a large number of straight wrinkles perpendicular to the cracks. The morphological characteristic, formation mechanism and evolution behaviors of the localized wrinkled stripes have been described and discussed in detail.

Designing highly efficient oxygen evolution reaction electrocatalyst of high-entropy oxides FeCoNiZrOx: Theory and experiment.

The correlations between the experimental methods and catalytic activities are urgent to be defined for the design of highly efficient catalysts. In this work, a new oxygen evolution reaction electrocatalyst of high-entropy oxide (HEO) FeCoNiZrOx was designed and analyzed by experimental and theoretical methods. On account of the shortened coordinate bond along with the increased annealing temperature, the atomic/electronic structures of active site were adjusted quantitatively with the aid of the pre-designed correlator of d electron density, which contributed to adjust the catalytic activity of HEO specimens. The prepared HEO specimen exhibited the low overpotentials of 245 mV at 10 mA cm-2 and 288 mV at 100 mA cm-2 with small Tafel slope of 35.66 mV dec-1, fast charge transfer rate, and stable electrocatalytic activity. This strategy would be adopted to improve the catalytic activity of HEO by adjusting the d electron density of transition metal ions with suitable preparation method.

Theoretical Study of Am(III) and Eu(III) Separation by a Bipyridyl Phosphate Ligand.

Actinide An(III) and lanthanide Ln(III) are known to exhibit similar chemical properties; thus, it is difficult to distinguish them in the separation of highly radioactive waste liquids. One potential method to efficiently separate actinides and lanthanides involves the design and development of phosphorus-oxygen-bonded ligands with solvent extraction separation. Here, a bipyridine phosphate ligand with two isopropyl and phosphate groups is introduced to selectively extract actinides. The electronic structure, bonding properties, thermodynamic behavior, and quantum theory of atoms in molecules (QTAIM) of Am(III) and Eu(III) complexes with the bipyridine phosphate ligands were analyzed by using density functional theory (DFT) calculations. The analysis demonstrates that the Am-N bond exhibits stronger covalent characteristics than the Eu-N bond, indicating that the bipyridine phosphate ligand had better selectivity for Am(III) than for Eu(III) in terms of binding affinity. The thermodynamic analysis established the complex [ML(NO3)2(H2O)2]+ as the most stable species during the complexation process. The results indicate great potential for utilizing the bipyridine phosphate ligand for the effective separation of An(III)/Ln(III) in spent fuel reprocessing experiments.

Strain driven enhancement of ferroelectricity and magnetoelectric effect in multiferroic tunnel junction.

The strain effect on the ferroelectric and magnetoelectric coupling in multiferroic tunnel junction (MFTJ) Co/BaTiO3/Co has been investigated systematically by using first-principles calculations within density functional theory. It is found that both in-plane compressive strain and uniaxial tensile strain lead to the enhancement of ferroelectric polarization stability and intensity of magnetoelectric coupling in the MFTJ. There is a transition from the paraelectric phase to the ferroelectric phase for the BaTiO3 layer in MFTJ when the loaded in-plane compressive strain increases up to -2.8% and the corresponding average ferroelectric polarization is about 0.13 C m(-2). Meanwhile, the calculated surface magnetoelectric coefficients increase with increasing in-plane compressive strain. Similar phenomena have been also observed in the case of uniaxial tensile strain implemented in MFTJ. The results suggest that the ferroelectric polarization and magnetoelectric coupling in multiferroic tunnel junctions can be controlled by strain and we expect that this study can provide a theoretical basis for the design of spintronic devices.

High-performance flexible strain sensors based on silver film wrinkles modulated by liquid PDMS substrates.

Flexible strain sensors based on controllable surface microstructures in film-substrate systems can be extensively applied in high-tech fields such as human-machine interfaces, electronic skins, and soft robots. However, the rigid functional films are susceptible to structural destruction and interfacial failure under large strains or high loading speeds, limiting the stability and durability of the sensors. Here we report on a facile technique to prepare high-performance flexible strain sensors based on controllable wrinkles by depositing silver films on liquid polydimethylsiloxane (PDMS) substrates. The silver atoms can penetrate into the surface of liquid PDMS to form an interlocking layer during deposition, enhancing the interfacial adhesion greatly. After deposition, the liquid PDMS is spontaneously solidified to stabilize the film microstructures. The surface patterns are well modulated by changing film thickness, prepolymer-to-crosslinker ratio of liquid PDMS, and strain value. The flexible strain sensors based on the silver film/liquid PDMS system show high sensitivity (above 4000), wide sensing range (∼80%), quick response speed (∼80 ms), and good stability (above 6000 cycles), and have a broad application prospect in the fields of health monitoring and motion tracking.

Preparation of a Hybrid TiO2 and 1T/2H-MoS2 Photocatalyst for the Degradation of Tetracycline Hydrochloride.

Water pollution caused by antibiotics is a growing problem. Semiconductor photocatalysis is an environmentally friendly technology that can effectively degrade organic pollutants in water. Therefore, the development of efficient photocatalysts is of great significance to solve the environmental pollution problem. In this paper, mixed-phase TiO2 and 1T/2H-MoS2 composite (1T/2H-MoS2/TiO2) were synthesized by the in situ growth method. The prepared compounds were characterized and applied to the visible-light degradation of tetracycline hydrochloride. The photocatalytic effect of 1T/2H-MoS2/TiO2 on tetracycline hydrochloride is significantly enhanced under visible light and has good stability. It has potential applications in the treatment of organic pollutants in water.

Epitaxial growth of hexahedral Fe2O3@SnO2 nano-heterostructure for improved lithium-ion batteries.

Fe2O3 is one of the most important lithium storage materials and has attracted increasing interest owing to its good capacity in theory, abundant reserves, and better security. The utilization of Fe2O3 materials is hampered by their inferior cycle performance, low rate performance, and restricted composite variety. Herein, the heterostructure of Fe2O3@SnO2 with hexahedral structure was manufactured by two- step hydrothermal strategy, while the SnO2 nanopillars were epitaxially grown in six faces, not in the twelve edges of hexahedral Fe2O3 cubes, which comes from maximizing lattice matching on the six surfaces of Fe2O3. Furthermore, the experimental results prove that the hexahedral Fe2O3@SnO2 heterostructure exhibits remarkably enhanced electrochemical reversibility and reaction kinetics and delivers an impressive initial discharge capacity (1742 mA h g-1 at 4 A g-1), great rate performance (565 mA h g-1 at 5 A g-1), and stable long-term durability (661 mA h g-1 after 4000 cycles at 4 A g-1) as an anode for LIBs. The result of the finite element mechanical simulation further indicates that the SnO2 nanopillars grow on the six surfaces but not on the twelve edges of the hexahedral Fe2O3 cube, which would provide great rate performance and long-term stability. This study underlines the merits of the heterostructure and offers a useful design routine for superior electrode materials in LIBs.

Stabilized and Almost Dendrite-Free Li Metal Anodes by In Situ Construction of a Composite Protective Layer for Li Metal Batteries.

Li metal anodes (LMAs) are promising candidates for the anodes of high-energy-density batteries due to their lower reduction potential and high specific capacity. Unfortunately, LMAs usually suffer from uncontrollable Li plating and insecure solid electrolyte interphase layers, especially when used in conjunction with carbonate-based electrolytes. Herein, we proposed using metal alkoxides of titanium butyrate to react with hydroxyl groups on Li metal. A composite protective layer containing TiO2 and ROLi was generated to modify Li (designated as treated Li), leading to dendrite-free LMAs and achieving significantly enhanced cycling stability. Notably, symmetric cells using treated Li electrodes can deliver over 1500 h of stable cycling under a current density of 2 mA cm-2 in an ether-based electrolyte. Moreover, under extreme conditions of 5 mA cm-2 using a carbonate-based electrolyte, symmetric cells employing a treated Li electrode demonstrated stable cycling for over 80 h, as compared to the fluctuating voltage seen after only 10 h of cycling when using a bare Li electrode. Furthermore, full cells using a treated Li anode coupled with a high loading of LiCoO2 cathode (≈15 mg cm-2) displayed excellent cycling stability at 0.2 C over 150 cycles with a high capacity retention of 98.1% and an enhanced average Coulombic efficiency above 99.6%. By comparison, full cells using the bare Li anode drop to 125.4 mA h g-1 with a capacity retention of just 83.3%. The treated Li exhibited superior rate performance and delivered 132.7 mA h g-1 even at 5 C. This strategy provided a facile and effective option for the construction of advanced LMAs.

Nonvolatile electrical control of 2D Cr2Ge2Te6 and intrinsic half metallicity in multiferroic hetero-structures.

The electrical control of two-dimensional (2D) van der Waals ferromagnets is a step forward for the realization of spintronic devices. However, using this approach for practical applications remains challenging due to its volatile memory. Herein, we adopt an alternative strategy, where the bistable ferroelectric switches (P↑ and P↓) of Sc2CO2 (SCO) assist the ferromagnetic states of Cr2Ge2Te6 (CGT) in order to achieve non-volatile memories. Moreover, MXene SCO, being an aided layer in multiferroic CGT/SCO hetero-structures, also modifies the electronic properties of CGT to half metal by its polarized P↓ state. In contrast, the P↑ state does not change the semiconducting nature of CGT. Hence, non-volatile, electrical-controlled switching of ferromagnetic CGT can be engineered by the two opposite ferroelectric states of single layer SCO. Importantly, the magnetic easy axis of CGT switches from in-plane to out-of-plane when the direction of electric polarization of SCO is altered from P↓ to P↑.

In Situ Growth of Metallic 1T-MoS2 on TiO2 Nanotubes with Improved Photocatalytic Performance.

1T-MoS2 is in situ grown on TiO2 nanotubes (TNTs) using a hydrothermal method, forming a 1T-MoS2@TNTs composite, which is confirmed by its physical characterization. The prepared composites show enhanced photocatalytic performance for the degradation of tetracycline hydrochloride under visible light, and the improved photocatalytic activity is closely related to the loaded amount of 1T-MoS2. Therein, 0.5 wt % 1T-MoS2@TNTs can degrade 57% in 1 h, which is the highest photocatalytic efficiency observed in experiments so far. It is speculated that the introduction of 1T-MoS2 may optimize light absorption and charge separation/transport. The active species are identified and the reaction mechanism is proposed here.

Coexistence of Ferroelectricity and Ferromagnetism in One-Dimensional SbN and BiN Nanowires.

Ferroelectricity exists in a variety of three- and two-dimensional materials and is of great significance for the development of electronic devices. However, the presence of ferroelectricity in one-dimensional materials is extremely rare. Here, we predict ferroelectricity in one-dimensional SbN and BiN nanowires. Their polarization strengths are 1 order of magnitude higher than ever reported values in one-dimensional structures. Moreover, we find that spontaneous spin polarization can be generated in SbN and BiN nanowires by moderate hole doping. This is the first time the coexistence of both ferroelectricity and ferromagnetism in a one-dimensional system has been reported. Our finding not only broadens the family of one-dimensional ferroelectric materials but also offers a promising platform for novel electronic and spintronic applications.

Ferroelectric control of single-molecule magnetism in 2D limit.

The electric control of magnetic properties based on magnetoelectric effect is crucial for the development of future data storage devices. Here, based on first-principles calculations, a strong magnetoelectric effect is proposed to effectively switch on/off the magnetic states as well as alter the in-plane/perpendicular easy axes of metal-phthalocyanine molecules (MPc) by reversing the electric polarization of the underlying two-dimensional (2D) ferroelectric α-In2Se3 substrate with the application of an external electric field. The mechanism originates from the different hybridization between the molecule and the ferroelectric substrate in which the different electronic states of surface Se layer play a dominant role. Moreover, the magnetic moments and magnetic anisotropy energies (MAE) of OsPc/In2Se3 can be further largely enhanced by a functionalized atom atop the OsPc molecule. The I-OsPc/In2Se3 system possesses large MAE up to 30 meV at both polarization directions, which is sufficient for room-temperature applications. These findings provide a feasible scheme to realize ferroelectric control of magnetic states in 2D limit, which have great potential for applications in nanoscale electronics and spintronics.

Large magnetoresistance and large magnetothermopower effect in the Dirac material EuMn0.8Sb2.

In this article, the structure, transport and magnetic properties were studied in details for EuMn0.8Sb2 crystals with the orthorhombic structure and Mn deficiencies. It was found that the temperature dependence of the resistivity exhibits a metallic behavior in the whole measuring temperature range, different from that in the crystals without Mn deficiencies. A large positive magnetoresistance (MR) (∼127% at 2 K and ∼25% at 300 K, in 9 T field) was observed, which can be ascribed to the combination of semiclassical MR and quantum limit MR of Dirac electrons. We also observed the high mobility of the carriers and large magnetothermopower effect at low temperatures, and two magnetic transitions emerging at ∼24 K and ∼10 K, respectively, corresponding to the antiferromagnetic ordering and canted arrangement of the Eu moments. Our findings shed new light on the intrinsic properties of EuMn0.8Sb2 and demonstrate the existence of Dirac fermions.

Electronic structures of ultra-thin tellurium nanoribbons.

The structural stability and electronic properties of monolayer and bilayer tellurium nanoribbons (TNRs) with different edge structures have been systematically investigated by means of first-principles calculations, revealing that the stability of both monolayer and bilayer TNRs largely rely on their width. Regardless of width, tip TNRs are metallic, while notch TNRs are p-type-like conductors. Interestingly, both mono- and bi-layer chain TNRs exhibit a semiconductor-to-metal transition as the width increases. The electronic structures of tip and notch TNRs are mainly determined by atomic reconstruction and the unsaturated electronic states on the edges. For chain TNRs, the origin of the semiconductor-to-metal transition can be attributed to the spontaneous in-plane electronic polarization across the ribbon. Our work reveals diverse electronic properties of one-dimensional elemental tellurium nanostructures, which considerably extend the potential applications of tellurene-based materials in nanodevices.

Tuning Interfacial Magnetic Ordering via Polarization Control in Ferroelectric SrTiO3/PbTiO3 Heterostructure.

The electromagnetic properties at the interface of heterostructure are sensitive to the interfacial crystal structure and external field. For example, the two-dimensional magnetic states at the interface of LaAlO3/SrTiO3 are discovered and can further be controlled by electric field. Here, we study two types of heterostructures, TiO2/PbTiO3 and SrTiO3/PbTiO3, using first-principle electronic structure calculations. We find that the ferroelectric polarization discontinuity at the interface leads to partially occupied Ti 3d states and the magnetic moments. The magnitude of the magnetic moments and the ground-state magnetic coupling are sensitive to the polarization intensity of PbTiO3. As the ferroelectric polarization of PbTiO3 increases, the two heterostructures show different magnetic ordering that strongly depends on the electron occupation of the Ti t2g orbitals. For the TiO2/PbTiO3 interface, the magnetic moments are mostly contributed by degenerated d yz/d xz orbitals of interfacial Ti atoms and the neighboring interfacial Ti atoms form ferromagnetic coupling. For SrTiO3/PbTiO3 interface, the interfacial magnetic moments are mainly contributed by occupied d xy orbital because of the increased polarization intensity, and as the electron occupation increases, there exists a transition of the magnetic coupling between neighboring Ti atoms from ferromagnetism to antiferromagnetism via the superexchange interaction. Our study suggests that manipulating the polarization intensity is one effective way to control interfacial magnetic ordering in the perovskite oxide heterostructures.

Spontaneous formation of hierarchical wrinkles in Cr films deposited on silicone oil drops with constrained edges.

We report on the spontaneous formation of hierarchical wrinkling patterns in Cr films deposited on silicone oil drops with constrained edges. The appearance of the wrinkling patterns is strongly dependent on the film thickness and the size of the silicone oil drop. Because the Cr film at the drop edge is constrained due to the strong adhesion between the film and the glass surface, the wrinkle wavelength merely depends on the distance starting from the drop edge. When the distance increases, the wavelength increases quickly first, and then it slows down gradually in compliance with a simple power law. The evolution of the wrinkle amplitude is similar to that of the wavelength, but it is also closely related to the film thickness and the oil drop size. Based on the fact that the silicone oil is polymerized to form an elastic layer during deposition, the formation and evolution of the hierarchical wrinkling patterns have been analyzed in detail.