Ferromagnetism in two-dimensional black phosphorus induced by phthalocyanine cobalt

Two-dimensional (2D) magnets have been the recent research focus due to their potential to meet requirements of continuous miniaturization of spintronic devices. However, very few intrinsic 2D ferromagnetic materials, in particular room-temperature magnets, have been demonstrated because of spin fluctuations and disturbed superexchange caused by the dimensional reduction. Herein, a synchronous ultrasonic exfoliation and doping method is proposed to fabricate ferromagnetic 2D black phosphorus (BP) through the adsorption of phthalocyanine cobalt (CoPc). The electron transfer from BP to CoPc is confirmed by X-ray photoelectron spectroscopy, which is believed to be responsible for the ferromagnetic ground state in as-doped BP (Co-BP) with a saturation magnetization of 0.18 emu g^?1. The density functional theory calculations well-support the charge transfer and the origin of ferromagnetism in Co-BP. In addition, the electron transfer results in the restricted activity of lone pair electrons, which might improve the antioxidant capacity of BP. Our study shed light on room-temperature ferromagnetism in 2D materials.

     

Ultrafast Laser‐Shock‐Induced Confined Metaphase Transformation for Direct Writing of Black Phosphorus Thin Films

Few‐layer black phosphorus (BP) has emerged as one of the most promising candidates for post‐silicon electronic materials due to its outstanding electrical and optical properties. However, lack of large‐scale BP thin films is still a major roadblock to further applications. The most widely used methods for obtaining BP thin films are mechanical exfoliation and liquid exfoliation. Herein, a method of directly synthesizing continuous BP thin films with the capability of patterning arbitrary shapes by employing ultrafast laser writing with confinement is reported. The physical mechanism of confined laser metaphase transformation is understood by molecular dynamics simulation. Ultrafast laser ablation of BP layer under confinement can induce transient nonequilibrium high‐temperature and high‐pressure conditions for a few picoseconds. Under optimized laser intensity, this process induces a metaphase transformation to form a crystalline BP thin film on the substrate. Raman spectroscopy, atomic force microscopy, and transmission electron microscopy techniques are utilized to characterize the morphology of the resulting BP thin films. Field‐effect transistors are fabricated on the BP films to study their electrical properties. This unique approach offers a general methodology to mass produce large‐scale patterned BP films with a one‐step manufacturing process that has the potential to be applied to other 2D materials.     

Facile synthesis of black phosphorus directly grown on carbon paper as an efficient OER Electrocatalyst: Role of Interfacial charge transfer and induced local charge distribution

Black phosphorus (BP), as a new 2D material, is normally synthesized by a high-pressure and high-temperature (HPHT) method from white and red phosphorus, which severely hinders the further development of BP for any potential applications and leads to search for other potential applications of BP with big challenge. Herein, we develop a facile and efficient Thermal-Vaporization-Transformation (TVT) approach to prepare a highly active BP directly grown on carbon paper as the electrode for Oxygen evolution reaction (OER), showing a low onset potential of 1.45 V versus RHE. Simultaneously, the current density of BP-CP illustrates the excellent electro-catalysis stability only decreases by 3.4% after continuous operation for 10000 s. Meanwhile, the density functional theory (DFT) calculations further illustrates the P-doped carbon layer in the upper side of BP layer is actually responsible for its enhanced OER property, and the adjacent carbon atoms of the embedded P atoms are actually the active sites due to the induced local change distribution by intramolecular change transfer. Considering the facile, but efficient and scalable, TVT approach can directly synthesize BP-CP with excellent OER performance, which is promising for BP electrocatalysts used for OER in metal-air batteries, fuel cells, water-splitting devices, even other key renewable energy.     

P25/Black phosphorus/Graphene hybrid for enhanced photocatalytic activity

A novel P25/Black phosphorus/Graphene hybrid has been successfully prepared by loading two components [P25 and Black phosphorus (BP)] on graphene nanosheets via a simple one-step hydrothermal method. The P25/BP/Graphene hybrids are characterized by scanning electron microscopy (SEM),Raman spectra and X-ray diffraction patterns, which confirm a good crystallized P25 and BP hybridization with graphene. Photoelectrochemical tests verify that the photocurrent density of as-prepared P25/BP/Graphene ternary hybrid (9.32 μA/cm²) is greatly improved at 1 V, which is nearly 34 times higher than that of sole P25 and 4.8 times as much as that of P25/Graphene. The improved photocatalytic activity is proposed to be benefited from the higher carrier mobility and additional accessible sites derive from the special configurations of ternary hybrid, as well as the introduction of the visible and near-infrared-activated BP photocatalyst. More importantly, this work demonstrates that the as-prepared P25/BP/Graphene hybrid would be an attractive candidate as high-performance photocatalyst, and provide positive proof of concept for developing the practical applications of graphene and black phosphorus based composites.     

Piezoelectricity in Multilayer Black Phosphorus for Piezotronics and Nanogenerators

Recently, piezoelectric characteristics have been a research focus for 2D materials because of their broad potential applications. Black phosphorus (BP) is a monoelemental 2D material predicted to be piezoelectric because of its highly directional properties and non-centrosymmetric lattice structure. However, piezoelectricity is hardly reported in monoelemental materials owing to their lack of ionic polarization, but piezoelectric generation is consistent with the non-centrosymmetric structure of BP. Theoretical calculations of phosphorene have explained the origin of piezoelectric polarization among P atoms. However, the disappearance of piezoelectricity in multilayer 2D material generally arises from the opposite orientations of adjacent atomic layers, whereas this effect is limited in BP lattices due to their spring-shaped space structure. Here, the existence of in-plane piezoelectricity is experimentally reported for multilayer BP along the armchair direction. Current–voltage measurements demonstrate a piezotronic effect in this orientation, and cyclic compression and release of BP flakes show an intrinsic current output as large as 4 pA under a compressive strain of −0.72%. The discovery of piezoelectricity in multilayer BP can lead to further understanding of this mechanism in monoelemental materials.     

Preparation of phosphorus targets using the compound phosphorus nitride

Commercially available phosphorus nitride (P₃N₅) shows a high oxygen content. Nevertheless, this material is attractive for use as phosphorus targets in experiments where red phosphorus would disappear due to its high vapor pressure and where a metal partner in the phosphite must be excluded due to its high atomic number. Methods are described to produce phosphorus nitrite targets by vacuum evaporation condensation.     

Stress-induced non-equilibrium grain boundary segregation of phosphorus in a Cr–Mo low alloy steel

Grain boundary segregation of phosphorus under a 40 MPa tensile stress at 520 °C in a 0.025 wt.% P-doped 2.25Cr1Mo steel, which has already been thermally equilibrated, is examined using Auger electron spectroscopy. The segregation of phosphorus during stress-ageing has a non-equilibrium characteristic, i.e. it is non-equilibrium segregation. The segregation level first increases with increasing stress-ageing time until about 0.5 h and then diminishes with further increasing stress-ageing time, leading the boundary concentration of phosphorus to return to its thermal equilibrium value after ageing for about 15 h. Therefore, the critical time for this non-equilibrium grain boundary segregation of phosphorus is about 0.5 h at which the segregation is peaked. At this critical time, the boundary concentration of phosphorus is about 20.5 at.%, which is about 4.5 at.% higher than its thermal equilibrium level. Xu's kinetic model for stress-induced grain boundary segregation [T.D. Xu, Philos. Mag. 83 (2003) 889–899; T.D. Xu, B.-Y. Cheng, Prog. Mater. Sci. 49 (2) (2004) 109–208] is used to analyse the experimental results, demonstrating that the measured data may be well simulated by the model.     

Sensitive Detection of Carcinoembryonic Antigen Using Stability‐Limited Few‐Layer Black Phosphorus as an Electron Donor and a Reservoir

The instability of few‐layer black phosphorus (FL‐BP) hampers its further applications. Here, it can be demonstrated that the instability of FL‐BP can also be the advantage for application in biosensor. First, gold nanoparticle/FL‐BP (BP‐Au) hybrid is facilely synthesized by mixing Au precursor with FL‐BP. BP‐Au shows outstanding catalytic activity (K = 1120 s^?1 g^?1) and low activation energy (17.53 kJ mol^?1) for reducing 4‐nitrophenol, which is attributed to the electron‐reservoir and electron‐donor properties of FL‐BP, and synergistic interaction of Au nanoparticles and FL‐BP. Oxidation of FL‐BP after catalytic reaction is further confirmed by transmission electron microscope, X‐ray photoelectron spectroscopy, and zeta potentials. Second, the catalytic activity of BP‐Au can be reversibly switched from “inactive” to “active” upon treatment with antibody and antigen in solution, thus providing a versatile platform for label‐free colorimetric detection of biomarkers. The sensor shows a wide detection range (1 pg mL^?1 to –10 µg mL^?1), high sensitivity (0.20 pg mL^?1), and selectivity for detecting carcinoembryonic antigen (CEA). Finally, the biosensor has been used to detect CEA in colon and breast cancer clinical samples with satisfactory results. Therefore, the instability of BP can also be the advantage for application in detecting cancer biomarker in clinic.     

Avalanche Carrier Multiplication in Multilayer Black Phosphorus and Avalanche Photodetector

A highly sensitive avalanche photodetector (APD) is fabricated by utilizing the avalanche multiplication mechanism in black phosphorus (BP), where a strong avalanche multiplication of electron–hole pairs is observed. Owing to the small bandgap (0.33 eV) of the multilayer BP, the carrier multiplication occurs at a significantly lower electric field than those of other 2D semiconductor materials. In order to further enhance the quantum efficiency and increase the signal‐to‐noise (S/N) ratio, Au nanoparticles (NPs) are integrated on the BP surface, which improves the light absorption by plasmonic effects. The BP–Au‐NPs structure effectively reduces both dark current (≈10 times lower) and onset of avalanche electric field, leading to higher carrier multiplication, photogain, quantum efficiency, and S/N ratio. For the BP–Au‐NPs APD, it is obtained that the external quantum efficiency (EQE) is 382 and the responsivity is 160 A W^‐1 at an electric field of 5 kV cm^‐1 (V_d ≈ 3.5 V, note that for the BP APD, EQE = 4.77 and responsivity = 2 A W^‐1 obtained at the same electric field). The significantly increased performance of the BP APD is promising for low‐power‐consumption, high‐sensitivity, and low‐noise photodevice applications, which can enable high‐performance optical communication and imaging systems.     

Controlling Structural Anisotropy of Anisotropic 2D Layers in Pseudo‐1D/2D Material Heterojunctions

Chemical vapor deposition and growth dynamics of highly anisotropic 2D lateral heterojunctions between pseudo‐1D ReS₂ and isotropic WS₂ monolayers are reported for the first time. Constituent ReS₂ and WS₂ layers have vastly different atomic structure, crystallizing in anisotropic 1T′ and isotropic 2H phases, respectively. Through high‐resolution scanning transmission electron microscopy, electron energy loss spectroscopy, and angle‐resolved Raman spectroscopy, this study is able to provide the very first atomic look at intimate interfaces between these dissimilar 2D materials. Surprisingly, the results reveal that ReS₂ lateral heterojunctions to WS₂ produce well‐oriented (highly anisotropic) Re‐chains perpendicular to WS₂ edges. When vertically stacked, Re‐chains orient themselves along the WS₂ zigzag direction, and consequently, Re‐chains exhibit six‐fold rotation, resulting in loss of macroscopic scale anisotropy. The degree of anisotropy of ReS₂ on WS₂ largely depends on the domain size, and decreases for increasing domain size due to randomization of Re‐chains and formation of ReS₂ subdomains. Present work establishes the growth dynamics of atomic junctions between novel anisotropic/isotropic 2D materials, and overall results mark the very first demonstration of control over anisotropy direction, which is a significant leap forward for large‐scale nanomanufacturing of anisotropic systems.     

Quasi‐Monolayer Black Phosphorus with High Mobility and Air Stability

Black phosphorus (BP) exhibits thickness‐dependent band gap and high electronic mobility. The chemical intercalation of BP with alkali metal has attracted attention recently due to the generation of universal superconductivity regardless of the type of alkali metals. However, both ultrathin BP, as well as alkali metal‐intercalated BP, are highly unstable and corrode rapidly under ambient conditions. This study demonstrates that alkali metal hydride intercalation decouples monolayer to few layers BP from the bulk BP, allowing an optical gap of ≈1.7 eV and an electronic gap of 1.98 eV to be measured by photoluminescence and electron energy loss spectroscopy at the intercalated regions. Raman and transport measurements confirm that chemically intercalated BP exhibits enhanced stability, while maintaining a high hole mobility of up to ≈800 cm² V^?1 s^?1 and on/off ratio exceeding 10³. The use of alkali metal hydrides as intercalants should be applicable to a wide range of layered 2D materials and pave the way for generating highly stable, quasi‐monolayer 2D materials.     

Black Phosphorus/Platinum Heterostructure: A Highly Efficient Photocatalyst for Solar‐Driven Chemical Reactions

A 2D black phosphorus/platinum heterostructure (Pt/BP) is developed as a highly efficient photocatalyst for solar‐driven chemical reactions. The heterostructure, synthesized by depositing BP nanosheets with ultrasmall (≈1.1 nm) Pt nanoparticles, shows strong Pt–P interactions and excellent stability. The Pt/BP heterostructure exhibits obvious P‐type semiconducting characteristics and efficient absorption of solar energy extending into the infrared region. Furthermore, during light illumination, accelerated charge separation is observed from Pt/BP as manifested by the ultrafast electron migration (0.11 ps) detected by a femtosecond pump‐probe microscopic optical system as well as efficient electron accumulation on Pt revealed by in situ X‐ray photoelectron spectroscopy. These unique properties result in remarkable performance of Pt/BP in typical hydrogenation and oxidation reactions under simulated solar light illumination, and its efficiency is much higher than that of other common Pt catalysts and even much superior to that of conventional thermal catalysis. The 2D Pt/BP heterostructure has enormous potential in photochemical reactions involving solar light and the results of this study provide insights into the design of next‐generation high‐efficiency photocatalysts.     

Atomic‐Level Sculpting of Crystalline Oxides: Toward Bulk Nanofabrication with Single Atomic Plane Precision

The atomic‐level sculpting of 3D crystalline oxide nanostructures from metastable amorphous films in a scanning transmission electron microscope (STEM) is demonstrated. Strontium titanate nanostructures grow epitaxially from the crystalline substrate following the beam path. This method can be used for fabricating crystalline structures as small as 1–2 nm and the process can be observed in situ with atomic resolution. The fabrication of arbitrary shape structures via control of the position and scan speed of the electron beam is further demonstrated. Combined with broad availability of the atomic resolved electron microscopy platforms, these observations suggest the feasibility of large scale implementation of bulk atomic‐level fabrication as a new enabling tool of nanoscience and technology, providing a bottom‐up, atomic‐level complement to 3D printing.     

Synergistically Coupling Black Phosphorus Quantum Dots with MnO2 Nanosheets for Efficient Electrochemical Nitrogen Reduction Under Ambient Conditions

The electrochemical nitrogen reduction reaction (NRR) is a promising strategy of nitrogen fixation into ammonia under ambient conditions. However, the development of electrochemical NRR is highly bottlenecked by the expensive noble metal catalysts. As a representative 2D nonmetallic material, black phosphorus (BP) has the valence electron structure similar to nitrogen, which can effectively adsorb the inactive nitrogen molecule and activate its triple bond. In addition, the relatively weak hydrogen adsorption can restrict the competitive and vigorous hydrogen evolution reaction. Herein, ultrafine BP quantum dots (QDs) are prepared via liquid‐phase exfoliation and then assembled on catalytically active MnO₂ nanosheets through van der Waals interactions. The obtained BP QDs/MnO₂ catalyst demonstrates admirable synergetic effects in electrochemical NRR. The monodisperse BP QDs providing major activity manifest excellent ammonia production steadily with high selectivity, which benefits from the robust confinement of the BP QDs on the wrinkled MnO₂ nanosheets with decent activity. A high ammonia yield rate of 25.3 µg h^?1 mg_cat.^?1 and faradic efficiency of 6.7% can be achieved at ?0.5 V (vs RHE) in 0.1 m Na₂SO₄ electrolyte, which are dramatically superior to either component. The isotopic labelling and other control tests further exclude the external contamination possibility and attest the genuine activity.     

Black Phosphorus Quantum Dots Cause Nephrotoxicity in Organoids,Mice, and Human Cells

Quantum dots (QDs) have numerous potential applications in lighting, engineering, and biomedicine. QDs are mainly excreted through the kidney due to their ultrasmall sizes; thus, the kidneys are target organs of QD toxicity. Here, an organoid screening platform is established and used to study the nephrotoxicity of QDs. Organoids are templated from monodisperse microfluidic Matrigel droplets and found to be homogeneous in both tissue structure and functional recapitulation within a population and suitable for the quantitative screening of toxic doses. Kidney organoids are proved displaying higher sensitivity than 2D‐cultured cell lines. Similar to metal‐containing QDs, black phosphorus (BP)‐QDs are found to have moderate toxicity in the kidney organoids. The nephrotoxicity of BP‐QDs are validated in both mice and human renal tubular epithelial cells. BP‐QDs are also found to cause insulin insensitivity and endoplasmic reticulum (ER) stress in the kidney. Furthermore, ER stress‐related IRE1α signaling is shown to mediate renal toxicity and insulin insensitivity caused by BP‐QDs. In summary, this work demonstrates the use of constructed kidney organoids as 3D high‐throughput screening tools to assess nanosafety and further illuminates the effects and molecular mechanisms of BP‐QD nephrotoxicity. The findings will hopefully enable improvement of the safety of BP‐QD applications.     

Chemical vapor deposition of amorphous molybdenum sulphide on black phosphorus for photoelectrochemical water splitting

Non-precious metal electrocatalyst molybdenum sulphide(MoS) and black phosphorus(BP) are highly promising catalysts for H₂ evolution reaction(HER).However,BP is environmentally unstable and the basal planes of crystal MoS₂ are inactive toward HER.Herein,amorphous molybdenum sulphide(MoSx)directly on BP/BiVO4 film dramatically improves the performance of photoelectrochemical water splitting compared with pure BiVO4.Additionally,we demonstrate that a BP layer,inserted between the MoSx and BiVO4,can enhance the photoelectrochemical performance and improve the stability of the electrodes.Finally,MoS_x/B P/BVO electrode shows the excellent current density of 2.1 mA/cm² at the potential of 1.2 V(vs Ag/AgCl),which is twice higher than that of pure BVO electrode.Our novel nanostructure materials will lead to a new class of non-precious metal photocatalysts for hydrogen production.     

Black phosphorus induced photo-doping for high-performance organic-silicon heterojunction photovoltaics

In conventional crystalline silicon (Si) homojunction solar cells,a strategy of doping by transporting phosphorus or boron impurities into Si is commonly used to build Ohmic contacts at rear electrodes.However,this technique involves an energy intensive,high temperature (～ 800 ℃) process and toxic doping materials.Black phosphorus (BP) is a two-dimensional,narrow bandgap semiconductor with high carrier mobility that exhibits broad light harvesting properties.Here,we place BP:zinc oxide (ZnO) composite films between Si and aluminum (Al) to improve their contact.Once the BP harvests photons with energies below 1.1 eV from the crystalline Si,the ZnO carrier concentration increases dramatically due to charge injection.This photo-induced doping results in a high carrier concentration in the ZnO film,mimicking the modulated doping technique used in semiconductor heterojunctions.We show that photo-induced carriers dramatically increase the conductivities of the BP-modified ZnO films,thus reducing the contact resistance between Si and Al.A photovoltaic power conversion efficiency of 15.2％ is achieved in organic-Si heterojunction solar cells that use a ZnO:BP layer.These findings demonstrate an effective way of improving Si/metal contact via a simple,low temperature process.     

Investigation of black phosphorus as a nano-optical polarization element by polarized Raman spectroscopy

Manipulating the polarization of light at the nanoscale is essential for the development of nano-optical devices. Owing to its corrugated honeycomb structure, two-dimensional (2D) layered black phosphorus (BP) exhibits outstanding in-plane optical anisotropy with distinct linear dichroism and optical birefringence in the visible region, which are superior characteristics for ultrathin polarizing optics. Herein, taking advantage of polarized Raman spectroscopy, we demonstrate that layered BP with a nanometer thickness can remarkably alter the polarization state of a linearly-polarized laser and behave as an ultrathin optical polarization element in a BP-Bi₂Se₃ stacking structure by inducing the exceptionally polarized Raman scattering of isotropic Bi₂Se₃. Our findings provide a promising alternative for designing novel polarization optics based on 2D anisotropic materials, which can be easily integrated in microsized all-optical and optoelectronic devices.

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Recovery Mechanism of Degraded Black Phosphorus Field‐Effect Transistors by 1,2‐Ethanedithiol Chemistry and Extended Device Stability

Black phosphorus (BP) has drawn enormous attention for both intriguing material characteristics and electronic and optoelectronic applications. In spite of excellent advantages for semiconductor device applications, the performance of BP devices is hampered by the formation of phosphorus oxide on the BP surface under ambient conditions. It is thus necessary to resolve the oxygen‐induced degradation on the surface of BP to recover the characteristics and stability of the devices. To solve this problem, it is demonstrated that a 1,2‐ethanedithiol (EDT) treatment is a simple and effective way to remove the bubbles formed on the BP surface. The device characteristics of the degraded BP field‐effect transistor (FET) are completely recovered to the level of the pristine cases by the EDT treatment. The underlying principle of bubble elimination on the BP surface by the EDT treatment is systematically analyzed by density functional theory calculation, atomic force microscopy, and X‐ray photoelectron spectroscopy analysis. In addition, the performance of the hexagonal boron nitride‐protected BP FET is completely retained without changing device characteristics even when exposed to 30 d or more in air. The EDT‐induced recovering effect will allow a new route for the optimization of electronic and optoelectronic devices based on BP.     

Silver‐Laden Black Phosphorus Nanosheets for an Efficient In Vivo Antimicrobial Application

Nanobactericides represent one of the most efficient and promising strategies for eliminating bacterial infection considering the increasing resistance threats of conventional antibiotics. Black phosphorus (BP) is the most exciting postgraphene layered 2D nanomaterial with convincing physiochemical properties, yet the study of BP‐based antibiotics is still in its infancy. Here, a compact silver nanoparticle (AgNP)–doped black phosphorus nanosheet (BPN) is constructed to synergistically enhance solar disinfection through the promoted reactive oxygen species (ROS) photogeneration, which is attributed to the improved electron–hole separation and recombination of BPNs as revealed from the systematic experimental studies. An in‐depth density functional theory (DFT) calculation confirms that the integrated AgNPs provide a preferred site for facilitating the adsorption and activation of O₂, thus promoting the more efficient and robust ROS generation on BPN–AgNP nanohybrids. Besides the enhanced photoinduced ROS, the anchored AgNPs simultaneously lead to a dramatically increased affinity toward bacteria, which facilitates a synergetic pathogen inactivation. Significantly, the convincing antimicrobial BPN–AgNP contributes to the prominent wound healing and antimicrobial ability in vivo with minimized biological burden. This sophisticated design of new 2D nanohybrids opens a new avenue for further exploiting BP‐based nanohybrids in portable bandage and broad‐spectrum disinfection applications.