Surface States Research Articles

Key roles of surface Cr in the NiFe layered double hydroxides for an efficient oxygen evolution reaction via adaptive reconfiguration

Cr doping is a new strategy to enhance the OER (Oxygen Evolution Reaction) performance of NiFe-LDH (NiFe-Layered Double Hydroxides) by optimizing surface states and offering a scalable production process. However, as an additive element, Cr itself has weak OER performance, so its promotion on the Ni- and Fe-active site by electron perturbation and structural stabilization in NiFeCr-LDH has been the focus. Herein, a one-step hydrothermal method is used to incorporate Cr into NiFe-LDH, systematically investigating the relationship between Cr content and the material's microstructure. The results of physical characterization show that Cr ion plays a leading role in the electron perturbation Ni/Fe-active center, which causes the increasing of Fe3+ and Ni3+ content. Furthermore, variations in Cr content resulted in the lattice stretching and morphology evolving synchronously. The optimized NiFeCr-LDH exhibited significantly enhanced OER activity and durability compared to undoped NiFe-LDH and outperformed commercial RuO2 catalysts. Additionally, a microstructure comparison was made between the initial- and long-term used-NiFeCr-LDH. The findings reveal that the material's distinctive structural evolution behavior confers it with exceptional self-adaptability to the OER reaction, which results in a consistent enhancement of activity lasting up to 12 h during long-term I-t test showing a new idea for the design of high performance NiFeCr-LDH.

Топологические изоляторы в электронных и спинтронных устройствах

Background: Topological insulators (TIs) are materials with distinctive features, including insulating interiors and conducting surface states protected by time-reversal symmetry. These features make TIs extremely promising for electrical and spintronic device applications, where manipulating electron spin without charge transfer is advantageous. Objective: This study aims to investigate of TIs to improve the performance and efficiency of electrical and spintronic devices. We look at the special qualities of TIs that may be used to improve device functionality, such as reduced power consumption and higher operational speed. Methods: To investigate electron transport behaviour on the surfaces of different TIs, we used a mix of quantum mechanical models and experimental settings. Devices based on bismuth telluride (Bi2Te3) and thallium arsenide (TlAs) were built to test their performance in real-world applications. Results: TI devices showed considerable gains in spin transport efficiency and thermal stability compared to conventional materials. Spintronic devices based on TIs demonstrated a 50% reduction in energy usage and a 30% improvement in data processing speed. Conclusion: Including topological insulators in electrical and spintronic devices offers a promising path to more efficient and speedier technologies. Future research should concentrate on the scalable integration of TIs into commercial devices and the discovery of novel materials with topological insulating characteristic.

One-step hydrothermal synthesis of F,N,S-doped photoluminescent carbon dots with yellowish-orange emission for sensitive Cu2+ ion detection: Environmental and biomedical applications

Herein, fluorine-, nitrogen-, and sulfur-doped carbon dots (FNS-CDs) were prepared via a one-step hydrothermal synthesis using flufenamic acid and thiourea as precursors, which showed yellowish-orange fluorescence both in aqueous solution and in the solid state. The as-prepared FNS-CDs were monodisperse and had an average diameter of 4 nm, good water solubility, a fluorescence quantum yield of 18.63 %, and excellent pH and ionic strength stability. The optimal excitation/emission wavelengths of the FNS-CDs were 406/570 nm, with an excitation-dependent wavelength range of 365–435 nm. The surface states, morphologies, and elemental compositions of the FNS-CDs were characterized using FTIR, XRD, TEM, and XPS. In addition, the FNS-CDs without any further modification exhibited high selectivity and sensitivity as nanosensors for Cu2+ over other metal ions. The PL quenching phenomenon can be used to detect Cu2+ ions within a linear range of 1–25 μM with a detection limit of 83.10 nM and an association constant of 1.29 × 104 M−1. The PL of the FNS-CDs was significantly quenched by Cu2+ ions through static quenching and was restored upon the subsequent addition of EDTA. The practical application was demonstrated through the detection of Cu2+ ions in real water samples, yielding recovery rates ranging from 97.8 % to 103.9 % with an RSD below 2.5 %. The FNS-CDs/Cu2+ complex exhibits potent antibacterial activity against S. aureus (85.27 %±2.1 %) and E. coli (91.31 %±1.6 %), whereas the FNS-CDs/Cu2+ has a higher inhibitory effect on the growth of E. coli. Furthermore, the FNS-CDs (100 μg/mL) were used for cell imaging, showing low toxicity to HCT-116 cells exhibited yellowish-orange fluorescence under a confocal microscope.

Influence of surface state on interface bonding strength of Al/Ta laminated composite via differential temperature rolling

Al/Ta laminated composite is one of the promising space radiation shielding materials. However, due to significant differences in the properties of Al and Ta alloys, the interface bonding strength of rolled Al/Ta laminated composites is weak. In this study, we prepared 2A12 Al/Ta-2.5W laminated composite using differential temperature rolling method. The influence of surface state on the interface microstructure and interface bonding strength were systematically analyzed, and the interface bonding mechanism of Al/Ta laminated composite was revealed. It is found that 2A12 Al and Ta-2.5W alloys are successfully bonded via differential temperature rolling within rolling temperature range of 350∼450 °C and rolling reduction range of 40 %–50 % when the hardening degree of Ta-2.5W surface layer exceeds 25 %, and the roughness of Ta-2.5W and 2A12 Al surface is greater than 4.5 μm and 3.6 μm, respectively. It is demonstrated that increasing the hardening degree and roughness at Ta-2.5W surface, while decreasing the hardening degree and increasing roughness at 2A12 Al surface can facilitate cracking of the surface layer at Ta-2.5W side and the embedding of virgin Al metal into the cracks during rolling, which can promote the interface bonding process between 2A12 Al and Ta-2.5W alloys. The highest interfacial bonding strength of Al/Ta laminated composite can reach 41.2 MPa. However, when the surface layer at Ta-2.5W side is excessively hardened and the hardness reaches two times of the substrate, thick fragments could be generated at the interface, which have detrimental effect on the interface bonding strength and the value decreases to 23.05 MPa. In terms of the effects of rolling temperature and rolling reduction, it is found that the oxide film and hardening layer on the Ta-2.5W surface are more sufficiently ruptured, and more virgin 2A12 Al metals are embedded in the cracks at the surface of Ta-2.5W at higher rolling temperature and higher rolling reduction conditions, thereby leading to the increased interface bonding strength. This study provides theoretical basis for the preparation of Al/Ta laminated composites and sheds light on the relationship between surface state and interface bonding strength of laminated metal composites.

Effect of chemical etching time on the fatigue behavior of Ti‐6Al‐4V produced by laser powder bed fusion

AbstractThis study focuses on the evolution of the fatigue strength of Laser Powder Bed Fusion (L‐PBF) produced Ti‐6Al‐4V as a function of the chemical etching finishing process. The aim is to identify the critical fatigue crack initiation mechanisms and the transitions between them in terms of the evolution of the surface micro‐geometry. This is done using three different geometries and six different surface states. The evolution of the crack initiation mechanisms is then used to explain the evolutions of the fatigue strength and the fatigue scatter. Chemical etching affects the fatigue life via a polishing effect, which directly influences both the finite and the high cycle fatigue domains. It is shown that chemical etching makes it possible to obtain fatigue strengths that are almost similar to those of the machined surface. However, it is also observed that etching cannot fully counteract the effects of large surface cavities caused by surface connected porosities.

Dimensionality-mediated type-II Dirac semimetal to quantum spin Hall insulator phase transition in TiC

We present first-principles results on monolayer (ML) and bulk titanium carbide (TiC) exhibiting dual topological characteristics: a quantum spin Hall insulator state in two-dimensional ML and a type-II Dirac semimetal state in its three-dimensional bulk form. The nontrivial nature of ML TiC is confirmed through the calculation of a Z2 invariant, spin Hall conductivity, and edge states. The edge band structure of ML TiC displays a single pair of gapless edge states at the M point. The insulating topological phase in ML TiC is driven by a band inversion around the M point involving Ti-d orbitals, with a nontrivial band gap of 0.47 eV. Our findings also indicate that ML TiC possesses excellent dynamical and thermal stability. Moreover, the bulk, ML hollow sphere arrays, and a 4-nm-thick film of TiC have already been synthesized, suggesting the high feasibility of the experimental synthesizing of ML TiC. On the other hand, we demonstrate that the bulk TiC hosts both a type-II Dirac cone and a topological nodal surface without spin-orbit coupling, protected by a combined symmetry of inversion and time reversal. The presence of spin-orbit coupling removes the nodal surface while preserving the type-II Dirac cone. Surface states connecting bulk Dirac nodes in bulk TiC can be readily observed, making the surface characteristics easily detectable in experiments. Published by the American Physical Society 2024

Ideal quadratic nodal point in half-Heusler semimetal LaPtBi

The research focus on topological states in electronic systems has recently expanded from traditional linear dispersions to encompass higher-order dispersions. These higher-order dispersions exhibit unique physical properties, including high topological charge, exotic magnetoresponse, and novel transport behaviors. In this study, we employ first-principles calculations to propose the half-Heusler material LaPtBi as an ideal quadratic nodal point semimetal. Our comprehensive analysis of the band structure reveals an ideal nodal point located precisely at the Fermi level, exhibiting quadratic dispersion in all directions. This finding is supported by symmetry analysis and effective model arguments. Moreover, when the spin-orbit coupling effect is considered, the nodal point transitions from triple to quadruple degeneracy, while maintaining its quadratic dispersion. The material also features multiple prominent arc surface states originating from the nodal point, which are distinctly separated from the bulk bands. This separation facilitates experimental verification. Overall, LaPtBi, with its quadratic nodal point and advantageous properties, serves as an ideal platform for further research. The study of this material is expected to enhance our understanding of higher-order topological states in electronic systems, potentially driving future advancements in the field.

Using Pseudo-Color Maps and Machine Learning Methods to Estimate Long-Term Salinity of Soils

Soil salinity assessment methods based on remote sensing data are a common topic of scientific research. However, the developed methods, as a rule, estimate relatively small areas of the land surface at certain moments of the season, tied to the timing of ground surveys. Considerable variability of weather conditions and the state of the earth surface makes it difficult to assess the salinity level with the help of remote sensing data and to verify it within a year. At the same time, the assessment of salinity on the basis of multiyear data allows reducing the level of seasonal fluctuations to a considerable extent and revealing the statistically stable characteristics of cultivated areas of land surface. Such an approach allows, in our opinion, the processes of mapping the salinity of large areas of cultivated lands to be automated considerably. The authors propose an approach to assess the salinization of cultivated and non-cultivated soils of arid zones on the basis of long-term averaged values of vegetation indices and salinity indices. This approach allows revealing the consistent relationships between the characteristics of spectral indices and salinization parameters. Based on this approach, this paper presents a mapping method including the use of multiyear data and machine learning algorithms to classify soil salinity levels in one of the regions of South Kazakhstan. Verification of the method was carried out by comparing the obtained salinity assessment with the expert data and the results of laboratory tests of soil samples. The percentage of “gross” errors of the method, in other words, errors when the predicted salinity class differs by more than one position compared to the actual one, is 22–28% (accuracy is 0.78–0.72). The obtained results allow recommending the developed method for the assessment of long-term trends of secondary salinization of irrigated arable land in arid areas.

Electrochemical Platform Based on the Bi2Te3 Family of Topological Insulators for the Detection of SARS-CoV-2 Pathogenic Factors.

Accurate and rapid detection of the causative agent of a disease is of great importance in controlling the spread of the disease. This work developed a biosensor with the Bi2Te3 family of topological insulators for detection of the SARS-CoV-2 virulence factor. The Bi2Te3 family is a three-dimensional topological insulator material with topologically protected surface states; the presence of these surface states facilitates charge transfer between the electrode and electrolyte interface. Compared with the detection performance of Bi2Se3, BiSbTeSe2, and a trivial insulator like Sb2Se3, Bi2Te3 exhibits superior characteristics. A Bi2Te3 electrochemical detection platform is utilized to fabricate a sensor that can detect SARS-CoV-2 DNA, RNA, and antigen for label-free target detection. The concentration range of DNA detection by the biosensor using Bi2Te3 is between 1.0 × 10-15 and 1.0 × 10-10 M, and the detection limit can reach 1.41 × 10-16 M. Furthermore, it exhibits excellent selectivity and maintains good stability even after being stored for 14 days. This study provides a new way to apply topological insulator materials in the field of biosensors and use their unique electronic structure to improve the accuracy and speed of disease detection and diagnosis.

Surface Electronic Structure of Cr Doped Bi2Se3 Single Crystals

Here, by using angle-resolved photoemission spectroscopy, we showed that Bi2−xCrxSe3 single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms in which a large nonmagnetic gap with a distorted band structure was reported. We further provide laser-based high resolution photoemission data which reveal a Dirac point gap even in the pristine sample. The gap becomes more pronounced with Cr doping into the bulk of Bi2Se3. These observations show that the Dirac point can be modified by the magnetic impurities as well as the light source.

Chern bands with higher-order Van Hove singularities on topological moiré surface states

Chern bands with higher-order Van Hove singularities on topological moiré surface states

Nonlinear characteristics and radial-bending-torsional vibration of a blade with breathing crack

Rotor failures due to cracked blades are frequently observed in rotating machinery. The identification of cracking state of rotating blade based on vibration characteristics has garnered a lot of attention. However, nonlinear characteristics and vibration combining in radial, bending and torsional directions of a rotating blade induced by the crack breathing is yet not clear. This paper proposes a radial-bending-torsional dynamic model of rotating blade with breathing crack. A time-varying integration method is proposed for determining the crack state based on the strain energy release rate. The crack breathing behavior is described by Boolean operation and the numerical integration are applied to open or close the crack. The model is validated through modal analysis, vibration responses and contact state of crack surface. Frequency veering is changed between the 2nd flap and 1st edgewise frequency due to the existence of crack. Strong nonlinear behaviors are found in the radial and torsional vibrations because of the crack breathing. Nonlinearities are also found in the combined vibrations between the radial-bending and the bending-torsional directions. Radial and torsional vibration amplitude levels can be used as an indication of blade crack failure, but the applicability depends on the absolute response decided by the aerodynamic excitation and resonant vibration. These findings can serve as guidance in crack identification and cracking state monitoring of rotating blades.

Three-dimensional valley-contrasting sound.

Spin and valley are two fundamental properties of electrons in crystals. The similarity between them is well understood in valley-contrasting physics established decades ago in two-dimensional (2D) materials like graphene-with broken inversion symmetry, the two valleys in graphene exhibit opposite orbital magnetic moments, similar to the spin-1/2 behaviors of electrons, and opposite Berry curvature that leads to a half topological charge. However, valley-contrasting physics has never been explored in 3D crystals. Here, we develop a 3D acoustic crystal exhibiting 3D valley-contrasting physics. Unlike spin that is fundamentally binary, valley in 3D can take six different values, each carrying a vortex in a distinct direction. The topological valley transport is generalized from the edge states of 2D materials to the surface states of 3D materials, with interesting features including robust propagation, topological refraction, and valley-cavity localization. Our results open a new route for wave manipulation in 3D space.

Pore structure regulation of nano-CdSnO3 based on particles adhesion and mass transfer for enhanced NO-sensing

CS-x (x = 1, 2, 4, 6) nanoparticles have been successfully prepared by simple hydrothermal method combined with calcination process, and the calcination time is adjusted to optimize micro-structure characterization for their enhanced NO-sensing. The techniques of XRD, Raman, SEM, TEM, TGA, DSC, BET, and XPS are used to study their phase structure, micro-morphology, thermal decomposition process and surface states, then the possible gas-sensitive mechanism is analyzed. Results show that the typical CS-2 sensor has the maximum response of 130–50 ppm NO at 90 ℃, the short response/recovery time of 40/45 s, and the low detection limit of 0.1 ppm (1.18). It also has the reliable NO selectivity against to other interfering gases, good repeatability and high stability. Its enhanced NO-sensing performance may be due to the optimization of pore structure by adjusting the calcination process based on particles adhesion and mass transfer, which increases the pore size and specific surface area that could provide the channel and active sites for gas diffusion and adsorption, thus further promoting the gas-sensing reaction. The experimental methods and ideas of pore structure regulation provide a new way for the design of high-performance sensitive materials.

Synthesis of carbon dots with tailored heteroatomic structure for achieving ultrahigh effectiveness in persulfate activation

Carbon dots (CDs) are normally feature with zero-dimensional structure, excellent solubility, good biosafety, and exceptional photoelectronic properties, thus, awakening the homogeneous-like photocatalytic potency of CDs in peroxymonosulfate (PMS) activation can afford new idea for water body remediation. Herein, we presented a facile nitrogen and sulfur co-doping strategy for the development of high-performance CDs-based photocatalysts. Through the deep investigation on the structure-activity relationship, we proposed that the incorporated pyridinic N within CDs structure could serve as efficient Lewis basic sites for PMS confinement. Importantly, the co-existence of oxidized sulfur groups and specific nitrogen speciation (pyridine N and pyrrolic N) induced unique “push-pull” effect on the photogenerated carriers within the surface state of S,N co-doped CDs. The unique synergy sites and surface hydrophilic nature conferred the CDs exceptional photocatalytic effectiveness, presenting a remarkable PMS consumption ratio of 7.62 per gram of the CDs photocatalyst within just 20 min. Profited from the improved kinetics of interfacial reactions, the CDs-photocatalyzed oxidation system that consisted largely of sulfate radicals can completely degrade rhodamine B within 12.5 min, and hold great potential in long-term operation without needing to regenerate CDs catalyst.

Topological van der Waals Contact for Two-Dimensional Semiconductors.

The relentless miniaturization inherent in complementary metal-oxide semiconductor technology has created challenges at the interface of two-dimensional (2D) materials and metal electrodes. These challenges, predominantly stemming from metal-induced gap states (MIGS) and Schottky barrier heights (SBHs), critically impede device performance. This work introduces an innovative implementation of damage-free Sb2Te3 topological van der Waals (T-vdW) contacts, representing an ultimate contact electrode for 2D materials. We successfully fabricate p-type and n-type transistors using monolayer and multilayer WSe2, achieving ultralow SBH (∼24 meV) and contact resistance (∼0.71 kΩ·μm). Simulations highlight the role of topological surface states in Sb2Te3, which effectively mitigate the MIGS effect, thereby significantly elevating device efficiency. Our experimental insights revealed the semiohmic behavior of Sb2Te3 T-vdW contacts, with an exceptional photoresponsivity of 716 A/W and rapid response times of approximately 60 μs. The findings presented herein herald topological contacts as a superior alternative to traditional metal contacts, potentially revolutionizing the performance of miniaturized electronic and optoelectronic devices.

The effect of degeneration of elastic fibres on loss of elasticity and wrinkle formation.

Skin elasticity, which is vital for a youthful appearance, depends on the elastic fibres in the dermis. However, these fibres deteriorate with ageing, resulting in wrinkles and sagging. Changes that occur in the elastic fibres in living human skin and the relationship between elastic fibres and the state of the skin surface remain unclear. Therefore, it is necessary to verify the relationship between elastic fibres and skin elasticity. In this study, we investigated the association of the elastic fibre structure with skin elasticity and stratum corneum protein content in living human skin. Thirty-five female volunteers aged 25-66 years were included in this study. Elastic fibres were observed using a multiphoton scanning laser biomicroscope. Skin elasticity was measured using a Cutometer, and stratum corneum proteins (Heat-shock protein 27 [HSP27] and galectin-7 [Gal-7]) in tape-stripped samples were analysed using an enzyme-linked immunosorbent assay. Elastic fibres exhibited increased curvature and thickness with increased age, with fragmentation observed in women aged >60 years. Elastin scores, which reflect thinness and curvature, were negatively correlated with age, whereas they were positively correlated with R7 elasticity (recovery ability). In individuals aged 20-30 years, higher levels of inflammatory markers (HSP27 and Gal-7) correlated with lower elastin scores; however, this trend was not observed in older participants. Elastic fibre deterioration worsened after 40 years of age, and this effect correlated with reduced skin recovery and increased wrinkles. In younger individuals, inflammatory markers affected elastic fibres. These findings can guide anti-ageing strategies that focus on elastic fibre preservation and inflammation control.

Ru-doped Mo2C grown on coconut shell derived 3D hierarchical carbon as robust electrocatalysts for hydrogen evolution reaction

Biomass, as a low-cost, environmental friendly and renewable carbon source with natural porous structure can be used as carriers. Molybdenum carbide (Mo2C), possessing metallic characteristics and a platinum-like d-band electronic structure, has recently emerged as promising candidate for hydrogen evolution reaction (HER). In this study, we fabricate a new electrocatalyst by embedding ruthenium (Ru) into Mo2C on carbonized coconut shell (Ru-Mo2C@CSC). Doping of Ru into Mo2C significantly activates the inherent HER activity by altering the surface state, which enhances electron accumulation and transfer between the intermediate and electrocatalyst surface. The obtained Ru-Mo2C@CSC exhibit a remarkably low overpotential of 40 mV at 10 mA cm−2 in 1 M KOH, matching the benchmark Pt/C. Both experimental and density functional theory (DFT) reveal that this outstanding electrocatalytic activity stems from its unique three-dimensional (3D) architecture and the altered electronic structure by Ru-doping. The distinct 3D hierarchical porous structure aids electrolyte penetration, increases exposure of active sites, and facilitates the release of gas products. Substituting Ru atoms notably diminish the proton adsorption strength at the Mo and C atom coordination sites and electronic modification of Mo by charge transfer from Ru to Mo which was observed by X-ray photoelectron spectroscopy. A synergetic interaction at the Ru-Mo interface is generated to optimize the adsorption–desorption energetics toward H intermediate and accelerate water dissociation.

Fluorescence Carbon Dots from Blood-Berries for Sensing Cr6+ Ions in Water and Application in White Light Emitting Diode.

Conventional techniques for identifying heavy metal ions in water are laborious and time-consuming. Therefore, it is necessary to create innovative sensing technologies that can detect with greater sensitivity and speed. Although there have been reports of optical-based assays utilising fluorescent nanomaterials, these assays usually rely on variations in signal strength. However, this approach has significant drawbacks when it comes to environmental monitoring. Fluorescence carbon dots (CDs) have been prepared by facile synthesis from Blood berries. A homemade heavy metal optical detector is constructed to accurately identify heavy metal ions, exclusively Cr6+ ions in a water medium. Their optical emission signature varies based on the specific chromium ions in solution, and the emission intensity also changes depending on its concentration. The quenching behaviour is attributed to the interaction between the metallic cations and the fluorescent surface states of the carbon dots. Another application is the encapsulation of CDs in PVDF polymer to form a flexible film and use it as a phosphor for LED conversion.

A coupling method for rapid, continuous and extremely wide-temperature measurement of total hemispherical emissivity and conversion efficiency of the kinetic energy of an electron beam to the thermal energy of a material based on a scanning electron beam

Precise measurements of a material's total hemispherical emissivity and conversion efficiency of the Kinetic energy of an Electron beam to the Thermal energy of a Material (KETM) are crucial for the advancement of new materials and electron beam applications. We propose a coupling method for the rapid and continuous measurements of the above parameters across an extremely broad temperature range, the basic idea of which is that a thin plate sample is uniformly heated to a high-temperature state by a scanning electron beam and naturally cooled, and equations of the transient heat transfer process in the cooling section and the heating section are solved separately based on the assumption of the lumped heat capacity, and the above parameters varying with temperature are obtained in turn. The characterization experiments of the wire-drawn and polished 304 stainless steel are carried out. The emissivities of two surface states increase monotonically in the ranges of [0.17(400K), 0.26(954K)] and [0.12(400K), 0.20(983K)], respectively, aligning well with trends and values reported in the literature. Oxidation on both surfaces worsens as the preset temperature rises, resulting in a corresponding increase in the emissivity. Considering the impact of oxidation on emissivity, KETM is calculated in various regions within the considered temperature ranges. The results indicate a slight variation around 0.819 in KETMs of wire-drawn and polished 304 stainless steel within the temperature range of 400∼1000 K, aligning well with the value reported in the literature. This efficient measurement method can provide potential support for the application of the above two parameters.