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Multilayer borophene was predicted to have a similar semiconductor property to its monolayer arise from the weak van der Waals interactions between the layers. Besides, multilayer borophene has a higher carrier mobility than monolayer ones, so it is placed great hopes in applications of photoelectric and photovoltaic devices. However, its preparation and application in experiments of multilayer borophene are still lacking. Here, multilayer α′-4H-borophene was synthesized on semiconducting n-type GaAs substrates using NaBH4 source as precursor and hydrogen as the carrier gas under controlled temperature and pressure conditions. The experimental results of the borophene are in good agreement with those of its theoretical prediction. The borophene is a semiconductor with a bandgap of 2.48 eV. To demonstrate the device application potential of the borophene, a near-infrared photodetector composed of p-type borophene and n-type GaAs was fabricated. The photodetector shows a high photoresponsivity of 0.31 mA•W-1, a high specific detectivity of 108 Jones, and a fast response or recovery speed of 117 or 109 ms under the irradiation with the wavelength of 940 nm at zero bias. The results prove that the α′-4H-borophene/GaAs photodetector can show high sensitivity and zero consumption, which is of great value in meeting the appeal of sustainable development of society.

Large-area borophene films have been controllably grown on a quartz substrate through a chemical vapor deposition process. A novel borophene hydroelectric generator was fabricated to harvest water energy and transform it into useful electricity.

High-performance gas sensing devices have been extensively studied in industrial production, clinical medicine and environmental monitoring. Among the materials used to fabricate gas sensors, two-dimensional (2D) materials are viewed as favorable candidate sensing materials because of their high surface-to-volume ratios, abundant surface activity, defect sites. However, gas sensors based on the previously reported 2D materials have some disadvantages such as poor air-stability and slow dynamic response. Recently, borophene, as a unique 2D material, has been theoretically predicted to have excellent gas sensing characteristic, especially for nitrogen dioxide (NO2). However, the gas sensing property of borophene has not been still reported experimentally. Here, we report that a chemiresistive sensor device based on borophene shows high sensitivity, fast response, high selectivity, good flexibility and long-time stability. It is found that the sensor has a low experimental detection limit of around 200 ppb, a large detection range from 200 ppb to 100 ppm, and fast response time of 30 s and recovery time of 200 s at room temperature, which are remarkably superior to those of reported 2D materials. The underlying NO2 sensing mechanism of borophene is revealed by first-principles calculations. In line with theoretical predication, it has also been confirmed experimentally that the borophene-based sensor has a unique selectivity to NO2 compared with other common gases. Furthermore, the sensor also displays superior flexibility and stability under different bending angles. This study shows excellent electronic and sensing characteristic of borophene, which indicates that it has great potential application value in high-performance sensing and detection in the future.

The growth of artificial synthesis two-dimensional (2D) materials usually demands for suitable substrate due to their rare bulk allotropies. Borophene, as a typical artificial synthetic material, has been proved its substrate-growth on metal or nonmetals and its high theoretical specific capacity (1720 mAh g−1) for next-genatration electrode material, but structural instability and transfer difficulties have hindered the development of its applications. Here, a structurally stable and freestanding AA-stacked-α′-4H-borophene sheets have been synthesized by in situ lithium eutectic salt-assisted synthetic method to realize the application of borophene in lithium-ion battery. The atomic structure of AA-α′-4H-borophene with interlayer VdWs was established by comparing the experimental observation with DFT optimal calculation. Different stacking configurations (AA- and AB-) of borophene was realized by a temperature-structure-photoluminescence intensity relationship, and the AA-stacked borophene exhibits higher specific capacity than AB structure. Based on electrochemical performance, the AA-borophene exhibits excellent rate capability and cycling performance due to its non-collapsible stacking configurations, which dominates great initial coulombic efficiency of 87.3% at 200 mA g−1 superior to that of black phosphorus-based and borophene/graphene. Meanwhile, it still maintains the coulombic efficiency of 99.13% after 1000 cycles. It also shows a reversible capacity of 181 mAh g−1 at 10 mA g−1 between the voltage window of 0.01 and 2 V, which improves the reported capacity (43 mAh g−1) of bulk boron anode by over 430%. This work brings fantastic new view of fabricating stable, stacking and freestanding borophene and provides a significative idea on applications of borophene in energy storage domain.

Borophene has attracted extensive interests owing to its distinct structural, electronic and optical properties for promising potential applications. However, the structural instability and need of metal substrate for deposition of borophene seriously restrict the exploration of its exceptional physical and chemical properties and further hamper its extensive applications towards high-performance electronic and optoelectronic devices. Here, we reported the synthesis of high-quality freestanding

Borophene has been proposed to be an energetic and promising material for electronic, optical, and thermal domains, but these applications have not been still achieved due to the metallic feature a...

Flexible and wearable electronic sensing devices play an increasingly important role in human health monitoring and non-contact sensors towards human to machine interface technologies. Humidity sensors have been proven to be effective in real-time respiratory monitoring and diagnostic analysis. The p–n junction of borophene–MoS2 has been theoretically predicted to have an ultrahigh humidity sensing characteristic, but the experiment is still not reported. Herein, we demonstrated experimentally a borophene–MoS2 heterostructured sensor with ultrahigh sensitivity, fast response, long life, good flexibility and high selectivity. Its sensitivity at a relative humidity (RH) of 97% is as high as 15 500%, which is more than 90 or 70 times higher than that of borophene or MoS2 alone. The sensitivity is the highest among all the reported chemiresistive sensors based on 2D materials. The corresponding swift response and recovery times are much lower than those of borophene or MoS2 alone. Additionally, the sensor shows superior flexibility under bending strain. Compared with other organic vapors, the sensor for water vapor exhibits outstanding selectivity. Besides, we also demonstrate the multifunctional applications of the sensor in human breath diagnosis and non-contact switch sensing systems, which indicates the potential of borophene-based sensors in future health care and human–machine interaction systems.

Zero-dimensional boron structures have always been the focus of theoretical research owing to their abundant phase structures and special properties. Boron clusters have been reported extensively by combining structure searching theories and photoelectron spectroscopy (PES) experiments; however, crystalline boron quantum dots (BQDs) have rarely been reported. Here, we report the preparation of large-scale and uniform crystalline semiconductor BQDs from the expanded bulk boron powders via a facile and efficient probe ultrasonic approach in the acetonitrile solution. The obtained BQDs have 2.46 nm average lateral size and 2.81 nm thickness. Optical measurements demonstrate that a strong quantum confinement effect occurs in the BQDs, implying the increase of the band gap from 1.80 eV for the corresponding bulk to 2.46 eV for the BQDs. By injecting the BQDs into poly(vinylpyrrolidone) as an active layer, a BQD-based memory device is fabricated that shows a rewriteable nonvolatile memory effect with a low transition voltage of down to 0.5 V and a high on/off switching ratio of 10

Boron atoms possess a short covalent radius and the flexibility to adopt sp2 hybridization, which favour the formation of diverse two-dimensional allotropes of boron. Several examples of such boron sheets with metallic nature have been reported recently. However, a semiconducting boron crystal with a direct bandgap is rarely reported either in bulk boron crystals or in two-dimensional boron sheets. Here, the boron sheets with a direct bandgap are synthesized on a Ni foil substrate by chemical vapor deposition. The boron sheets with 48 boron atoms per unit cell have a quasicubic structure, and they are semiconducting and have a direct bandgap of around 2.4 eV, which are verified by combining theoretical and experimental investigations. The result greatly expands the known allotropy of the fifth element and opens vast opportunities to design 2D boron sheets with tunable optical, electronic, magnetic and chemical properties.

Borophene has been predicted to have outstanding catalytic activity owing to its extreme electron deficiency and abundant active sites. However, no experimental results have been still reported for borophene application in high-efficiency catalysis. Here, a borophene nanosheet was prepared on a carbon cloth surface via chemical vapor deposition. The boron source is sodium borohydride and the carrier gas is hydrogen gas. The crystal structure of the borophene nanosheet highly matches that of a theoretical α'-borophene nanosheet. Borophene shows good electrocatalytic hydrogen evolution reaction (HER) ability with a 69 mV/dec Tafel slope and good cycling stability in a 0.5 M H

Borophene has attracted enormous attention because of its rich and unique structural and electronic properties for promising pratical applications. Although borophene sheets have been realized on different substrates in recent experiments, there are very few reports on the device application of borophene. Recently, borophene can be grown on some functional substrates, which lays a good foundation for its potential applications. Here, we report that hydrogenated borophene can be grown on the fluorine-doped tin oxide glass substrate. The phase of the obtained borophene is well consistent with the predicted semiconducting δ5-boron sheet. Furthermore, a vertical heterojunction ultraviolet detector based p-borophene/n-zinc oxide was fabricated. The photoresponsivity of the detector is 1.02× 10-2 AW-1, the specific detection rate was 4.51× 109 Jones and the response speed was τres = 2.8 s, τrec = 3.2 s at the reversed bias of -5 V under the light excitation of 365 nm. This work will lay a foundation for further study on the attractive properties and applications of borophene in new optoelectronic devices and integrated circuits.

Borophene has attracted extensive interests owing to its distinct structural, electronic and optical properties for promising potential applications. However, the structural instability and need of metal substrate for deposition of borophene seriously restrict the exploration of its exceptional physical and chemical properties and further hamper its extensive applications towards high-performance electronic and optoelectronic devices. Here, we reported the synthesis of high-quality freestanding α-rhombohedral borophene nanosheets by a facile probe ultrasonic approach in different organic solvents. The results show that the nanosheets have high-quality in ethanol solution and have an average lateral size of 0.54 μm and a thickness of around 1.2 nm. Photoluminescence spectra indicate that a strong quantum confinement effect occurs in the nanosheets, which caused the increase of the band gap from 1.80 eV for boron powders and 2.52 eV for the nanosheets s. A nonvolatile memory device based on the nanosheets mixed with polyvinylpyrrolidone was fabricated, which exhibited a good rewriteable nonvolatile memory behavior and good stability.

The emergence of borophene has triggered soaring interest in the investigation of its superior structural anisotropy, a novel photoelectronic property for diverse potential applications. However, the structural instability and need of a metal substrate for depositing borophene restrict its large-scale applications toward high-performance electronic and optoelectric devices. van der Waals epitaxy is regarded as an efficient technique for growing superb two-dimensional materials onto extensive functional substrates, but the preparation of stable and controllable borophene on nonmetallic substrates is still not reported. Here, we demonstrate that borophene films can be synthesized onto a mica substrate by van der Waals epitaxy, where hydrogen and NaBH4 are respectively used as the carrier gas and the boron source. The lattice structure of the as-synthesized borophene coincides with the predicted α'-boron sheet. The borophene-based photodetector shows an excellent photoresponsivity of 1.04 A W-1 and a specific detectivity of 1.27 × 1011 Jones at a reversed bias of 4 V under illumination of a 625 nm light-emitting diode, which are remarkably superior to those of reported boron nanosheets. This work facilitates further studies of borophene toward its attractive properties and applications in novel optoelectronic devices and integrated circuits.

Heterostructure has triggered a surge of interest due to its synergistic effects between two different layers, which contributes to desirable physical properties for extensive potential applications. Structurally stable borophene is becoming a promising candidate for constructing two-dimensional (2D) heterostructures, but it is rarely prepared by suitable synthesis conditions experimentally. Here, we demonstrate that a novel heterostructure composed of hydrogenated borophene and graphene can be prepared by heating the mixture of sodium borohydride and few-layered graphene followed by stepwise and in situ thermal decomposition of sodium borohydride under high-purity hydrogen as the carrier gas. The fabricated borophene-graphene heterostructure humidity sensor shows ultrahigh sensitivity, fast response, and long-time stability. The sensitivity of the fabricated borophene-based sensor is near 700 times higher than that of pristine graphene one at the relative humidity of 85% RH. The sensitivity of the sensor is highest among all the reported chemiresistive sensors based on 2D materials. Besides, the performance of the borophene-graphene flexible sensor maintains good stability after bending, which shows that the borophene-based heterostructures can be applied in wearable electronics. The observed high performance can be ascribed to the well-established charge transfer mechanism upon H2O molecule adsorption. This study further promotes the fundamental studies of interfacial effects and interactions between boron-based 2D heterostructures and chemical species.

Borophenes (2D boron sheets) have triggered a surge of interest both theoretically and experimentally because of its distinct structural, optical and electronic properties for extensive potential applications. Although theoretical efforts have guided the research directions of borophene, only few synthetic borophene sheets have been demonstrated experimentally. Borophene sheets have been successfully synthesized experimentally on metal substrates until 2015. Afterwards, more efforts were put on the controlled synthesis of crystalline and semiconducting borophene sheets as well as on the investigation of their novel and fascinating physical properties. This report provides a brief review on theoretical and experimental progress in borophene research. Some typical structures and properties of borophenes have been reviewed. The focus is laid on summarizing the experimental synthesis of borophene in recent years, and on showing some ultrastable and semiconducting borophenes which have been applied in electronic information devices. Finally, the future challenges and opportunities regarding experimental realization and practical applications of borophenes are presented.

Borophene sheets have been synthesized in recent experiments, but the metallic nature and structural instability of the sheets seriously prevent emerging applications. Hydrogenated borophene has been predicted as an ideal material for nanoelectronic applications due to its high stability as well as excellent electronic and mechanical properties. However, the fabrication of hydrogenated borophene is still a great challenge. Here, we demonstrate that hydrogenated borophenes in large quantities can be prepared without any metal substrates by a stepwise in-situ thermal decomposition of sodium borohydride under hydrogen as the carrier gas. The borophenes with good crystallinity exhibit superior stability in strong acid or base solvents. The structure of the grown borophene is in good agreement with the predicted semiconducting α-boron sheet. A fabricated borophene-based memory device shows a high ON/OFF-current ratio of 3×103 and a low operating voltage of less than 0.35 V as well as good stability.

Recently, two-dimensional (2D) boron nanosheets have been predicted to exhibit exceptional physical and chemical properties, which is expected to be widely used in advanced electronics, optoelectronic, energy storage and conversion devices. However, the experimental application of 2D boron nanosheets in hydrogen evolution reactiuon (HER) has not been reported. Here, we have grown ultrathin boron nanosheets on tungsten foils via chemical vapor deposition. The prepared triclinic boron nanosheets are highly crystalline, which perfectly match the structure in the previous theoretical calculations. Notably, the boron nanosheets show excellent HER performance. The Tafel slope is only 64 mV dec−1 and the nanosheets can maintain good stability under long-time cycle in acidic solution. The improvement of performance is mainly due to the metal properties and a large number of exposed active sites on the boron nanosheets, which is confirmed by first-principle calculations.

This paper proposes a novel outer-rotor flux-switching permanent-magnet (OR-FSPM) machine with specific wedge-shaped magnets for in-wheel light-weight traction applications. First, the geometric topology is introduced. Then, the combination principle of stator slots and rotor poles for OR-FSPM machines is investigated. Furthermore, to demonstrate the relationship between performance specifications (e.g., torque and speed) and key design parameters and dimensions (e.g., rotor outer diameter and stack length) of OR-FSPM machines at preliminary design stage, an analytical torque-sizing equation is proposed and verified by two-dimensional (2-D) finite-element analysis (FEA). Moreover, optimizations of key dimensions are conducted on an initially designed proof-of-principle three-phase 12-stator-slot/22-rotor-pole prototyped machine. Then, based on 2-D-FEA, a comprehensive comparison between a pair of OR-FSPM machines with rectangular- and wedge-shaped magnets and a surface-mounted permanent-magnet (SPM) machine is performed. The results indicate that the proposed OR-FSPM machine with wedge-shaped magnets exhibits better flux-weakening capability, higher efficiency, and wider speed range than the counterparts, especially for torque capability, where the proposed wedge-shaped magnets-based one could produce 40% and 61.5% more torque than the rectangular-shaped magnets-based machine and SPM machine, respectively, with the same rated current density (5 A/mm2). Finally, the predicted performance of the proposed OR-FSPM machine is verified by experiments on a prototyped machine.

In this paper, the significant influence of rotor-poles number on the electromagnetic performances of the novel rotor-permanent magnet flux-switching (RPM-FS) machine is investigated. The operation principles of the RPM-FS machines with 10-, 11-, 13- and 14-rotor-poles are analyzed from the generator and motor-driving perspectives, respectively, and the armature reaction field and PM field modulation results are also researched and illustrated in detail. Then, a comprehensive comparison of electromagnetic performances between four RPM-FS machines is conducted to evaluate the merits and disadvantages of machines. It can be found that the RPM-FS machines with 14-rotor-poles exhibits the highest torque density and the widest range of constant power. Further, the performances of the RPM-FS machine are verified by experimental results.

The semi-rigid base asphalt pavement has become the main form of high grade Highway pavement structure in China. But with changes in temperature, humidity and amount of traffic, serious cracking problems also exist in this pavement, affecting pavement performance. Analyses crack type of asphalt pavement and its causes, for serious reflection crack problem of semi-rigid base asphalt pavement, by on different structure type and different cement dose cement stabilized gravel mixture for indoor dry shrink and temperature shrink test research analyse variation law of its dry shrink strain, and dry shrink coefficient, and temperature shrink strain, and temperature shrink coefficient, ect. and provides basis to improve semi-rigid base asphalt pavement anti-crack performance.