Search

In-plane anisotropic two-dimensional (2D) materials, emerging as an intriguing type of 2D family, provide an ideal platform for designing and fabrication of optoelectronic devices. Exploring air-stable and strong in-plane anisotropic 2D materials is still challenging and promising for polarized photodetection. Herein, SiP2, a 2D IV-V semiconductor, is successfully prepared and introduced into an in-plane anisotropic 2D family. The basic characterizations combined with theoretical calculations reveal 2D SiP2 to exhibit an intrinsically low-symmetry structure, the in-plane anisotropy of phonon vibrations, and an anisotropically dispersed band structure. Moreover, the photodetector based on 2D SiP2 exhibits high performance with a high detectivity of 1012 Jones, a large light on/off ratio of 103, a low dark current of 10-13 A, and a fast response speed of 3 ms. Furthermore, 2D SiP2 demonstrates a high anisotropic photodetection with an anisotropic ratio up to 2. In addition, the polarization-sensitive photodetector presents a dichroic ratio of 1.6 due to the intrinsic linear dichroism. These good characteristics make 2D SiP2 a promising candidate as an in-plane anisotropic semiconductor for high-sensitivity and polarized optoelectronic applications.

Metal-free 2D phosphorus-based materials are emerging catalysts for ammonia (NH3 ) production through a sustainable electrochemical nitrogen reduction reaction route under ambient conditions. However, their efficiency and stability remain challenging due to the surface oxidization. Herein, a stable phosphorus-based electrocatalyst, silicon phosphide (SiP), is explored. Density functional theory calculations certify that the N2 activation can be realized on the zigzag Si sites with a dimeric end-on coordinated mode. Such sites also allow the subsequent protonation process via the alternating associative mechanism. As the proof-of-concept demonstration, both the crystalline and amorphous SiP nanosheets (denoted as C-SiP NSs and A-SiP NSs, respectively) are obtained through ultrasonic exfoliation processes, but only the crystalline one enables effective and stable electrocatalytic nitrogen reduction reaction, in terms of an NH3 yield rate of 16.12 µg h-1 mgcat. -1 and a Faradaic efficiency of 22.48% at -0.3 V versus reversible hydrogen electrode. The resistance to oxidization plays the decisive role in guaranteeing the NH3 electrosynthesis activity for C-SiP NSs. This surface stability endows C-SiP NSs with the capability to serve as appealing electrocatalysts for nitrogen reduction reactions and other promising applications. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Submitted/Accepted version Q.Y. acknowledges the funding support from Singapore MOE AcRF Tier 1 under grant no. 2020-T1-001-031 and Singapore A*STAR project A19D9a0096. C.X. thanks the support from the Ministry of Education Singapore under AcRF-Tier1 (2021-T1-002-012, RG65/21.

Terahertz (THz) technology has attracted great attention in the past few decades for its unique applications in various fields, including spectroscopy, noninvasive detection, wireless communications, and imaging. In parallel to this, the practical, fast, and broadband modulation of THz waves is becoming indispensable. Two‐dimensional (2D) materials exhibit unusual optical and electrical properties, which has prompted tremendous interest and significant advances in THz modulation. This review provides the recent progress in 2D materials‐based THz modulators, outlining the operating principles, including all‐optical, electro‐optic, magneto‐optic, and other exotic mechanisms. We focus on the recent advances in THz modulation by the designed photonic structures, such as heterostructure, metamaterial, capacitor, optical cavity, and waveguide integration. Lastly, we discussed the challenges and opportunities for 2D materials‐based THz modulators and presented our prospects for the future development.

Low-cost preparation of high-efficiency electrocatalysts is challenging the development of electrocatalytic water splitting. Here, amorphous nickel/nickel sulfide composite films with controlled Ni...

Three-dimensional perovskite AMX3 has great potential in photoelectric applications, but the poor stability is a major problem that restricts its practical application. The emergence of lower dimensional perovskite solves this problem. Here, we have synthesized a group of novel low-dimensional perovskites with diverse structures. Different amino acids were incorporated in the perovskite cage. The formulas of the compounds are (A')mPbIm+2 (A' = COOH(CH2)nNH2, n = 1, 3, 5, 7, 9). These families of materials demonstrate structure-related stability, tunable bandgap, and different photoluminescence. Single-crystal X-ray diffraction indicated that the five materials employ different structure types varying from edge-sharing structures to face- and corner-sharing Pb/I structures by adjusting the number of C atoms in organic cations, and the level of [PbI6]4- octahedral distortion was also identified. The film prepared using these materials with longer carbon chains (n = 5, 7, 9) showed better stability, and they did not decompose within one year at 75% RH, 40 °C. The bifunctional organic ions containing carboxyl groups as spacer cations will form additional hydrogen bonding between perovskite layers, resulting in higher stability of the material. The band gaps of these materials vary from 2.19 to 2.6 eV depending on the octahedral connection mode and [PbI6]4- octahedral distortion level, density functional theory calculations (DFT) are consistent with our experimental trends and suggest that the face-sharing structure has the maximum band gap due to its flatter electron band structure. Bright green fluorescence was observed in (COOH(CH2)7NH3)2PbI4 and (COOH(CH2)9NH3)2PbI4 when excited by 365 nm UV light. A thorough comprehension of the structure-property relationships is of great significance for further practical applications of perovskites.

A novel autonomous initial alignment for the stationary strapdown inertial navigation system (SINS) with the bio-inspired polarized skylight sensors (PSS) is proposed to improve the precision and convergence speed in this paper. A pair of perpendicularly polarized skylight sensors with six-channels are used to measure and calculate the polarization azimuth angles, which is finally constructed a new polarized measurement error equation. With the SINS error equations, the SINS/PSS integrated navigation error equations are developed to achieve autonomous and fast initial alignment. Two types of observability, geometric observability and stochastic observability, are introduced to evaluate the integrated navigation systems. The geometric observability, which is defined by calculating the rank of the observability matrix, is analysed. It is found that the integrated navigation systems are not completely observable. Further, the degree of observability based on singular value decomposition is also used to examine the observable degree of the SINS/PSS integrated navigation system. The stochastic observability is associated with observability analysis with the estimated precision of the designed filter. The Kalman filter is designed to estimate the unknown state based on the measurements from the inertial measurement unit and PSS. Simulations and experiments demonstrate that the SINS/PSS achieve a rapid initial alignment with higher precision. Compared with the SINS, the vertical misalignment angle accuracy of SINS/PSS is improved by more than 90%, and the time cost is shortened by 60% in the simulation test. For the initial alignment experiment, the vertical misalignment greatly improved the accuracy and shorten the time cost.

Titanium dioxide (TiO2) has been extensively investigated as a photocatalyst for water splitting to produce H2. However, an overall water splitting by using anatase TiO2 is extremely difficult due to the short lifetime of holes. In this work, we propose that a surface energy decrease from {001} to {101} of anatase TiO2 is able to drive an epitaxial growth. A novel anatase TiO2 homostructure has been successfully synthesized via a facile hydrothermal route, where {101} semi-pyramid nanoparticles epitaxially grew on the both sides of the {001} nanosheets. The epitaxial relationship between the nanoparticles and the nanosheets has been characterized to be {001}//{001} of anatase TiO2. For the first time, it is interesting to find that the homostructure with 12 wt% of {101} semi-pyramid can significantly improve the H2 evolution rate by nearly 5 times compared to the pure nanosheets under the ultraviolet irradiation. More importantly, such homostructure enables 10.78 μmol g−1 h−1 of O2 production whereas the pure nanosheets cannot evolve detectable O2 gas. Meanwhile, the time-resolved photoluminescence analysis indicates that the mean lifetime of the holes is increased from 2.20 ns of the nanosheets to 3.59 ns of the homostructure, accounting for the observed overall water splitting. The findings suggest that constructing a homostructure by a surface energy strategy could be promising towards overall water splitting, which may be applicable to other photocatalytic materials.

Molybdenum disulfide (MoS2) is one of the two-dimensional layered semiconductor transition metal dichalcogenides (TMDCs) with great potential in electronics, optoelectronics, and spintronic devices. Sulfur vacancies in MoS2 are the most prevalent defects. However, the effect of sulfur vacancies on the electronic structure of MoS2 is still in dispute. Here we experimentally and theoretically investigated the effect of sulfur vacancies in MoS2. The vacancies were intentionally introduced by thermal annealing of MoS2 crystals in a vacuum environment. Angle-resolved photoemission spectroscopy (ARPES) was used directly to observe the electronic structure of the MoS2 single crystals. The experimental result distinctly revealed the appearance of an occupied defect state just above the valence band maximum (VBM) and an upward shift of the VBM after creating sulfur vacancies. In addition, density functional theory (DFT) calculations also confirmed the existence of the occupied defect state close to the VBM as well as two deep unoccupied states induced by the sulfur vacancies. Our results provide evidence to contradict that sulfur vacancies indicate the origin of n-type behaviour in MoS2. This work provides a rational strategy for tuning the electronic structures of MoS2.

How to electrically control magnetic properties of a magnetic material is promising towards spintronic applications, where the investigation of carrier doping effects on antiferromagnetic (AFM) materials remains challenging due to their zero net magnetization. In this work, we found electron doping dependent variation of magnetic orders of a two-dimensional (2D) AFM insulator NiPS3, where doping concentration is tuned by intercalating various organic cations into the van der Waals gaps of NiPS3 without introduction of defects and impurity phases. The doped NiPS3 shows an AFM-ferrimagnetic (FIM) transition at doping level of 0.2-0.5 electrons/cell and a FIM-AFM transition at doping level of >= 0.6 electrons/cell. We propose that the found phenomenon is due to competition between Stoner exchange dominated inter-chain ferromagnetic order and super-exchange dominated inter-chain AFM order at different doping level. Our studies provide a viable way to exploit correlation between electronic structures and magnetic properties of 2D magnetic materials for realization of magnetoelectric effect., 18 pages, 7 figures

In-plane anisotropic two-dimensional (2D) materials, emerging as an intriguing type of 2D family, provide an ideal platform for designing and fabrication of optoelectronic devices. Exploring air-stable and strong in-plane anisotropic 2D materials is still challenging and promising for polarized photodetection. Herein, SiP

Purpose Multiple-source disturbances exist in the polarization sensor, which severely affect the sensor accuracy and stability. Hence, the disturbance analysis plays a vital role in improving the sensor orientation performance. This paper aims to present a novel sensor error model, a disturbances quantitative analysis, a calibration and performance test of polarization sensor based on a polarizing beam splitter. Design/methodology/approach By combining with the sensor coefficient errors, the Azimuth of Polarization (AoP) error model and the Degree of Polarization (DoP) error model are established, respectively. In addition, the multiple-source disturbances are classified, while the influence on the orientation accuracy is quantitative analyzed. Moreover, the least square optimization algorithm is employed to calibrate the sensor coefficients. Finally, an outdoor test is carried out to test the sensor long-term accuracy. Findings The theoretical analysis and numerical simulations illustrate that the sensor accuracy is closely related to the disturbances. To eliminate the influence of the disturbances, the least square optimization algorithm, which can minimize the sum of squares of the residual difference of AoP and DoP, is used to calibrate the sensor coefficients. The outdoor test indicates that the sensor can maintain long-term accuracy and stability. Originality/value The main contribution of this paper is to establish a novel sensor error model, where the sensor coefficient errors are introduced. In addition, the disturbances are classified and analyzed to evaluate the orientation accuracy of the sensor.

Direct deposition of isolated metal atoms onto substrates has been recognized as a simple route to obtain high performance supported atomically dispersed metals (SACs), however, the agglomeration driven by high surface energy is difficult to avoid. Herein, we demonstrate a one-pot solution synthesis to obtain atomically dispersed platinum (Pt) supported on nitrogen (N)-doped mesoporous carbon (NMC) substrates (Pt/NMC-LT) by conducting the whole synthesis at −40 °C, owing to the sluggish nucleation kinetics. We obtained the Pt/NMC-LT catalyst with superior electrochemical hydrogen evolution reaction (HER) activity and stability, in comparison with the NMC supported dominant Pt sub-nanometer cluster catalyst from solution synthesis at RT ∼ 25 °C (Pt/NMC-RT) and commercial carbon supported Pt nanoparticle catalysts (Pt/C). Lower over-potential values (only 17.0 and 49.8 mV) are needed for high HER current densities (10 and 100 mA cm−2, respectively), and no obvious degradation is observed after an accelerated durability test (ADT) for 5000 CV cycles.

High quality and large size nonlinear optical LiInS2 (LIS) crystals were successfully grown by the optimized seeded Bridgman method. And the optical properties and carrier dynamics of LIS in the THz range were investigated by THz time-domain spectroscopy (THz-TDS) in the temperature range of 20–300 K for the first time. The refractive index and absorption coefficients present obvious temperature dependent behavior. A distinct absorption peak was observed at around 1.68 THz, which can be attributed to the vibration of In–S bonds revealed by Raman spectroscopy analysis. And the carrier concentration, mobility and scattering rate also show obvious temperature dependent behavior. These results will provide further understanding of the optical properties of LIS crystals and a perspective for future applications of LIS crystals in THz technology.

It is well-known that the size of a catalyst has a huge influence on catalytic activity. Thus, developing an easy and inexpensive way to synthesize nanocatalysts with reduced size is very urgent. H...

Two-dimensional (2D) materials driven by their unique electronic and optoelectronic properties have opened up possibilities for their various applications. The large and high-quality single crystals are essential to fabricate high-performance 2D devices for practical applications. Herein, IV-V 2D GeP single crystals with high-quality and large size of 20 × 15 × 5 mm3 were successfully grown by the Bi flux growth method. The crystalline quality of GeP was confirmed by high-resolution X-ray diffraction (HRXRD), Laue diffraction, electron probe microanalysis (EPMA) and Raman spectroscopy. Additionally, intrinsic anisotropic optical properties were investigated by angle-resolved polarized Raman spectroscopy (ARPRS) and transmission spectra in detail. Furthermore, we fabricated high-performance photodetectors based on GeP, presenting a relatively large photocurrent over 3 mA. More generally, our results will significantly contribute the GeP crystal to the wide optoelectronic applications.

Recent studies often utilize the Graph Convolutional Network (GCN) to learn label dependencies features for the multi-label text classification (MLTC) task. However, constructing the static label graph according to the pairwise co-occurrence from training datasets may degrade the generalizability of the model. In addition, GCN-based methods suffer from the problem of over-smoothing. To this end, we propose a Residual Dynamic Graph Convolutional Network Model (RDGCN) (https://github.com/ilove-Moretz/RDGCN.git) which adopts a label attention mechanism to learn the label-specific representations and then constructs a dynamic label graph for each given instance. Furthermore, we devise a residual connection to alleviate the over-smoothing problem. To verify the effectiveness of our model, we conduct comprehensive experiments on two benchmark datasets. The experimental results show the superiority of our proposed model.

In this paper, to address the problem of positioning accumulative errors of the inertial navigation system (INS), a bionic autonomous positioning mechanism integrating INS with a bioinspired polarization compass is proposed. In addition, the bioinspired positioning system hardware and the integration model are also presented. Concerned with the technical issue of the accuracy and environmental adaptability of the integrated positioning system, the sun elevation calculating method based on the degree of polarization (DoP) and direction of polarization (E-vector) is presented. Moreover, to compensate for the latitude and longitude errors of INS, the bioinspired positioning system model combining the polarization compass and INS is established. Finally, the positioning performance of the proposed bioinspired positioning system model was validated via outdoor experiments. The results indicate that the proposed system can compensate for the position errors of INS with satisfactory performance.

Group IV–V 2D semiconductors, such as GeP and GeAs, have attracted increasing attention as a hot research topic due to their high in-plane anisotropic properties. As one among them, orthorhombic SiP (o-SiP) deserves more attention due to its sufficiently high carrier mobility, large band gap, excellent stability and even a direct band gap in the monolayer. In this work, the experimental Raman modes were identified based on DFT calculations and then we demonstrated highly in-plane anisotropy of the phonon vibrations by angle-resolved polarized Raman spectroscopy. In addition, o-SiP based photodetectors were fabricated to investigate the in-plane anisotropic photoresponse. The results indicate that o-SiP is an alternative photodetector with high responsivity and well-reproducible cycles. Furthermore, high anisotropy was revealed with a notably anisotropic on/off switching ratio. Our results show that o-SiP is a new member of the family of group IV–V 2D semiconductors with intriguing optoelectronic properties, and will open new opportunities for promising applications in advanced photonic and optoelectronic devices.

Mid-infrared (MIR) coherent light generated by nonlinear optical (NLO) materials is crucial for military and civilian applications. Among the MIR optical crystal family, the LiInSe2 (LISe) single crystal is a promising candidate due to its remarkable physical properties. Herein, a high-quality LISe crystal with the largest diameter of 31 mm was successfully grown by the Bridgman growth method using an oriented seed. The crystalline quality and optical homogeneity of LISe were demonstrated by high-resolution X-ray diffraction (HRXRD), Laue diffraction, and optical interferometry measurements, respectively. Additionally, a complete survey of the transmittance spectra, absorption coefficients, and refractive indices was systematically performed. Furthermore, we found that the absorption coefficients of LISe at 1.064 μm can be obviously decreased after thermal annealing under LISe atmospheric conditions. More generally, our results will contribute significantly to the practical applications of LISe in the MIR technology field.

As an environmentally friendly and chemically robust crystal, LiInSe2 (LISe) exhibits promising optoelectronic properties. Here, an ultrasensitive metal–semiconductor–metal (MSM) structured photodetector based on a high-quality LISe crystal was systemically investigated. Remarkably, the LISe based photodetectors exhibit an outstanding photosensitivity with a high on/off current ratio (6.80 × 104), fast photoresponse (trise = 180 μs and tdecay = 200 μs), and high detectivity (2.16 × 1012 Jones). This work may lay the foundation and ignite future research interest on chalcogenide crystals in photodetectors.

The global positioning and orientation determination of marine vehicles is a challenging issue, especially in the distant sea scenarios where global navigation satellite system (GNSS) and/or magnetic compass failure. In this paper, a self-contained interactive iteration positioning and orientation coupled navigation method based on skylight polarization is proposed. To be more specific, by fusing the e-vectors and the gravity vectors, the orientation determination step is presented. Accordingly, the pitch, yaw, and roll angles can be calculated, and introduced into the global positioning step. In combination with the two steps, a coupled iteration mechanism of global positioning solution and orientation determination based on skylight polarization is constructed. According to the coupled iteration mechanism, the polarization-based geolocation and orientation can be thereby calculated under the complex scenarios where the GNSS or magnetic compass are disturbed. Finally, a set of simulations and field tests are carried out to validate the performance of the method.

Single crystals of an environmental friendly material LiInSe2 (LISe) with dimensions up to Φ16 mm × 55 mm were grown successfully through a modified vertical Bridgman technique. The quality of the crystal was measured by a high resolution X-ray diffraction rocking curve, and a full width at half-maximum (fwhm) for a, b, and c faces are 47″, 46″, 36″, respectively. It indicates that the as-grown crystal is high quality. The complete sets of dielectric, elastic, and piezoelectric constants of LISe crystals at room temperature were obtained by the resonant technique and impedance analysis for the first time. The piezoelectric constants d24 and d33 reached −13.6 pC/N and 8.5 pC/N, respectively. The corresponding electromechanical coupling coefficient k33 is 21%. In addition, the structural distortions and dipole moments of LISe were analyzed in detail. Our results show that LISe is a promising candidate as an environmental friendly piezoelectric material.

Herein, a single crystal of FeSi4P4 (FSP) with dimensions up to 8 × 7 × 3 mm3 was successfully grown using a seeded flux growth method. Single crystal X-ray diffraction results revealed that the FSP crystal crystallized in the chiral space group P1 (no. 1). High-resolution X-ray diffraction presents a full-width at half-maximum (FWHM) of 36′′ and 46′′ for the (100) and (001) FSP crystals, respectively, which indicates that FSP crystals have high crystalline quality. FSP is thermally stable up to 1157.1 °C and has a high thermal conductivity of 35 W (m K)−1 at room temperature. The magnetic analysis shows that the FSP crystal is paramagnetic in the range from 5 to 300 K. The Hall effect measurement suggests that the FSP crystal is a promising p-type semiconductor at room temperature.

Two-dimensional (2D) materials have recently attracted great interest due to their promising optoelectronic applications. Orthorhombic SiP (o-SiP) is a 2D layered crystal and may have a significant impact on optoelectronic technologies. Large-sized bulk o-SiP single crystals have been successfully grown by a seeded flux method. The size and morphology of o-SiP crystals can be controlled by changing the growth conditions. The carrier mobility and band gap of o-SiP were characterized in detail. The photoresponse properties of o-SiP were investigated and a relatively fast response has been demonstrated. The experimental results indicate that o-SiP may be an excellent candidate for applications in electronics and optoelectronics.

In view of their high nonlinear optical coefficients and good phase-matching properties, CdSiP2 (CSP) crystals are considered as one of the most promising materials in the field of nonlinear optical applications. However, the slight absorption losses around 1.34 μm and 1.78 μm under e-polarized light have been affecting its performance. In this study, first-principles calculations were performed to identify the effects of various charge defects on the absorption properties. Different intrinsic defects in the CSP crystal were calculated using the HSE method and compared according to the specific chemical environments in the experiments. The results show that the point defects of V, Si, and V, which can be spontaneously formed, are dominant in the Cd-poor environment. The combination of Si and V defects is the most favorable cluster in the Cd-poor case because of its relatively low formation energy. Furthermore, the antisite defect SiCd was found to be responsible for the main absorption peaks at 1.34 and 1.78 μm in the experimental spectra, whereas other defects and clusters, such as the defects Si and V, also contribute to these red shifted absorptions. Our results intend to provide a guideline for adjusting the optical absorption in CSP by modifying its defects.

CaGdAlO4 (CGA) single crystals have been grown in different oxygen concentration atmospheres by the Czochralski method. Crystals grown under an oxygen-containing atmosphere presented an inconsistent brown coloration. The origin of coloration was studied by density functional theory, and the simulated results show the oxygen defects and the absorption matched well with the experimental results. The brown coloration of CGA is due to the interstitial oxygen atoms. The fundamental properties of CGA crystals with different colors, including the crystal density, hardness, thermal and optical properties, were systematically investigated and compared when taking into account the effect of color center inside. The colorless CGA was grown under an inert gas atmosphere and exhibits a wide transparency range of 227–7140 nm. The maximum phonon energy was determined to be as low as 618 cm−1. The colorless CGA host crystal with a disordered structure, good thermal conductivity, low maximum phonon energy and wide transparency is promising for ultrafast ultraviolet and visible laser applications.