Unzipping of black phosphorus to form zigzag-phosphorene nanobelts

Spintronic performance of bent zigzag phosphorene nanoribbons: effects of mechanical deformation and gate voltage

This study explores the spintronic properties of an innovative device incorporating in-plane bent zigzag phosphorene nanoribbons (ZPNRs). The device features ZPNRs with a channel length of 23.4 nm, bent into circular arcs with varying curvatures. We investigate the impact of mechanical deformation and gate voltage on the spin-dependent properties, including the density of states, transmission coefficients, and spin Seebeck coefficient (SSC). Our results demonstrate that the device exhibits a spin-semiconducting phase with tunable spin-splitting characteristics and spin-dependent transport properties, both of which are influenced by the curvature. An increase in the bending parameter markedly enhances spin splitting, leading to the SSC attaining values as high as 1.35 mV K-1. Moreover, the application of gate voltage further enhances both spin polarization and spin current. The significant impact of mechanical deformation and gate voltage on spintronic performance showcases the potential of bent ZPNRs for advanced applications.

Effective capture of As(V) from water by a facile one step hydrothermal synthesized of 2-D bismuthene quantum dots nanosorbent

Arsenic species have been known for their toxic impact on human. Therefore, removal of such pollutant requires efficient and effective removal methodology from polluted water. In this study, bismuthene quantum dots (Bi-ene-QDs) were fabricated by a green and facile one pot-hydrothermal conversion reaction of Bi(NO3)3·5H2O. Bi-ene-QDs exhibited semi-spherical crystalline providing 6.0 nm 157.78 m2/g. Consequently, As(V) capturing by Bi-ene-QDs revealed optimum practical conditions at pH 3, interaction duration time 40 min and 10 mg Bi-ene-QDs dosage. The interaction of As(V) ions with Bi-ene-QDs were confirmed by the appearance of As-O stretching vibration. Moreover, Bi-ene-QDs achieved excellent adsorptive capture percentages of Arsenic ions from sea, tap and wastewater providing 94.61, 95.21 and 94.38% from contaminated samples with 5 mg L-1 Arsenic ions. Therefore, Bi-ene-QDs can be categorized as an unprecedented and efficient nanosorbent for the successful removal of Arsenic ions pollution from various wastewater matrices with > 90.0% efficiency.

Scalable Fabrication of Black Phosphorous Films for Infrared Photodetector Arrays

Bulk black phosphorous (bP) exhibits excellent infrared (IR) optoelectronic properties, but most reported bP IR photodetectors are fabricated from single exfoliated flakes with lateral sizes of < 100 µm. Here, scalable thin films of bP suitable for IR photodetector arrays are realized through a tailored solution-deposition method. The properties of the bP film and their protective capping layers are optimized to fabricate bP IR photoconductors exhibiting specific detectivities up to 4.0 × 108 cm Hz1/2 W-1 with fast 30/60 µs rise/fall times under λ = 2.2 µm illumination. The scalability of the bP thin film fabrication is demonstrated by fabricating a linear array of 25 bP photodetectors and obtaining 25 × 25 pixel IR images at ≈203 ppi with good spatial fidelity. This research demonstrates a commercially viable method of fabricating scalable bP thin films for optoelectronic devices including room temperature-operable IR photodetector arrays.

Origins of Severe Structural Changes during Alloying-Dealloying Reactions in Black Phosphorus

Li-alloying reactions facilitate the incorporation of a large number of Li atoms into the crystalline structures of electrodes, such as black phosphorus (BP). However, the reactions inevitably induce multistep phase transitions characterized by drastic atomic rearrangements and lattice collapse. Despite many theoretical and experimental studies on alloying mechanisms, long-term debates persist regarding the structures of the intermediate phases, the accurate pathways of phase transitions, the formation of specific configurations, and alloying/dealloying reversibility. Here, through a combination of operando electron diffraction measurements and ab initio simulations at the atomic and electronic scales, we identify key factors that govern the severe structural changes during alloying-dealloying reactions in BP. P-P bonds of three-bond P atoms are continuously broken during lithiation, generating two-bond P atoms with a high ability to accept inserted electrons and Li ions. Consequently, the pristine layered structure in BP is transformed to P7 cages in Li3P7, which then evolve to chain configurations in LiP and finally to isolated P atoms in Li3P. Specifically, the preferential formation of the P7 cage results from its lowest binding energy with three Li ions compared to other cage isomers. Furthermore, only LiP can be reversibly transformed to the crystalline structure of Li3P7 during charge, but it is thermodynamically favorable for Li3P7 and Li3P intermediates to be delithiated to amorphous structures. Our findings offer unique insights into the alloying mechanisms and deepen the fundamental understanding of alloying anode systems.

Intercalation in 2D materials and in situ studies

Intercalation of atoms, ions and molecules is a powerful tool for altering or tuning the properties - interlayer interactions, in-plane bonding configurations, Fermi-level energies, electronic band structures and spin-orbit coupling - of 2D materials. Intercalation can induce property changes in materials related to photonics, electronics, optoelectronics, thermoelectricity, magnetism, catalysis and energy storage, unlocking or improving the potential of 2D materials in present and future applications. In situ imaging and spectroscopy technologies are used to visualize and trace intercalation processes. These techniques provide the opportunity for deciphering important and often elusive intercalation dynamics, chemomechanics and mechanisms, such as the intercalation pathways, reversibility, uniformity and speed. In this Review, we discuss intercalation in 2D materials, beginning with a brief introduction of the intercalation strategies, then we look into the atomic and intrinsic effects of intercalation, followed by an overview of their in situ studies, and finally provide our outlook.

Seeded growth of single-crystal black phosphorus nanoribbons

Two-dimensional materials have emerged as an important research frontier for overcoming the challenges in nanoelectronics and for exploring new physics. Among them, black phosphorus, with a combination of a tunable bandgap and high mobility, is one of the most promising systems. In particular, black phosphorus nanoribbons show excellent electrostatic gate control, which can mitigate short-channel effects in nanoscale transistors. Controlled synthesis of black phosphorus nanoribbons, however, has remained an outstanding problem. Here we report large-area growth of black phosphorus nanoribbons directly on insulating substrates. We seed the chemical vapour transport growth with black phosphorus nanoparticles and obtain uniform, single-crystal nanoribbons oriented exclusively along the [100] crystal direction. With comprehensive structural calculations, we discover that self-passivation at the zigzag edges holds the key to the preferential one-dimensional growth. Field-effect transistors based on individual nanoribbons exhibit on/off ratios up to ~104, confirming the good semiconducting behaviour of the nanoribbons. These results demonstrate the potential of black phosphorus nanoribbons for nanoelectronic devices and also provide a platform for investigating the exotic physics in black phosphorus.

Electrochemical exfoliation of 2D materials beyond graphene

After the discovery of graphene in 2004, the field of atomically thin crystals has exploded with the discovery of thousands of 2-dimensional materials (2DMs) with unique electronic and optical properties, by making them very attractive for a broad range of applications, from electronics to energy storage and harvesting, and from sensing to biomedical applications. In order to integrate 2DMs into practical applications, it is crucial to develop mass scalable techniques providing crystals of high quality and in large yield. Electrochemical exfoliation is one of the most promising methods for producing 2DMs, as it enables quick and large-scale production of solution processable nanosheets with a thickness well below 10 layers and lateral size above 1 μm. Originally, this technique was developed for the production of graphene; however, in the last few years, this approach has been successfully extended to other 2DMs, such as transition metal dichalcogenides, black phosphorous, hexagonal boron nitride, MXenes and many other emerging 2D materials. This review first provides an introduction to the fundamentals of electrochemical exfoliation and then it discusses the production of each class of 2DMs, by introducing their properties and giving examples of applications. Finally, a summary and perspective are given to address some of the challenges in this research area.

Recent advances in ambient-stable black phosphorus materials for artificial catalytic nitrogen cycle in environment and energy

Nitrogen cycle is crucial for the Earth's ecosystem and human-nature coexistence. However, excessive fertilizer use and industrial contamination disrupt this balance. Semiconductor-based artificial nitrogen cycle strategies are being actively researched to address this issue. Black phosphorus (BP) exhibits remarkable performance and significant potential in this area due to its unique physical and chemical properties. Nevertheless, its practical application is hindered by ambient instability. This review covers the synthesis methods of BP materials, analyzes their instability factors under environmental conditions, discusses stability improvement strategies, and provides an overview of the applications of ambient-stable BP materials in nitrogen cycle, including N2 fixation, NO3- reduction, NOx removal and nitrides sensing. The review concludes by summarizing the challenges and prospects of BP materials in the nitrogen cycle, offering valuable guidance to researchers.

Few-layer black phosphorus enables nitrogen fixation under ambient conditions

Nitrogen (N2) fixation is a key reaction in biological and industrial chemistry, which does not occur spontaneously under ambient conditions but often depends on very specific catalysts and harsh reaction processes. Here we show that exposing exfoliated black phosphorus to the open air triggers, concomitantly, the oxidation of the two-dimensional (2D) material and the fixation of up to 100 parts per million (0.01%) of N2 on the surface. The fixation also occurs in pristine non-exfoliated material. Besides, other allotropic forms of phosphorus, like red P, also fixes N2 during ambient oxidation, suggesting that the N2 fixation process is intrinsic with phosphorus oxidation and does not depend on the chemical structure or the dimensionality of the solid. Despite the low amounts of N2 fixed, this serendipitous discovery could have fundamental implications on the chemistry and environmental stability of phosphorous and the design of related catalysts for N2 fixation.

Investigating the mechanism of phosphorene nanoribbon synthesis by discharging black phosphorus intercalation compounds

Phosphorene nanoribbons (PNRs) can be synthesised in intrinsically scalable methods from intercalation of black phosphorus (BP), however, the mechanism of ribbonisation remains unclear. Herein, to investigate the point at which nanoribbons form, we decouple the two key synthesis steps: first, the formation of the BP intercalation compound, and second, the dissolution into a polar aprotic solvent. We find that both the lithium intercalant and the negative charge on the phosphorus host framework can be effectively removed by addition of phenyl cyanide to return BP and investigate whether fracturing to ribbons occurred after the first step. Further efforts to exfoliate mechanically with or without solvent reveal that the intercalation step does not form ribbons, indicating that an interaction between the amidic solvent and the intercalated phosphorus compound plays an important role in the formation of nanoribbons.

Thiol ligand-mediated exfoliation of bulk sulfur to nanosheets and nanodots: applications in antibacterial activity

Reducing bulk materials to layers or dots results in profound alterations in their physiochemical and optoelectronic properties, leading to a wide array of applications, spanning from device manufacturing to biomedicine. In this regard, the preparation of sulfur nanomaterials has garnered significant attention due to their low toxicity. Traditional methods for sulfur nanomaterial synthesis often involve harsh reaction conditions, leaving a gap for convenient approaches to create nanomaterials, such as nanosheets (NSs) and nanodots (NDs). Herein, the mechanical exfoliation of bulk sulfur using a surfactant thiol ligand with probe sonication is reported, making a unique contribution to existing methods. In the reported method, the thiol group binds to sulfur surfaces, facilitating exfoliation and stabilization, while the hydrophilic ends provide functional groups for exfoliated nanomaterials. Exfoliation can yield either nanosheets or nanodots, depending on the thiol ligand and exfoliation time. This approach offers the opportunity to exfoliate bulk sulfur using bioactive thiol ligands. With this goal in mind, bulk sulfur was exfoliated with 4-mercaptophenylboronic acid (BA) to target Gram-positive bacteria. This innovative exfoliation strategy of bulk sulfur using thiol ligands holds immense promise for synthesizing functionalized sulfur nanomaterials with wide-ranging applications, particularly in biomedicine.

Recent Advances in Phosphorene: Structure, Synthesis, and Properties

Phosphorene is a 2D phosphorus atomic layer arranged in a honeycomb lattice like graphene but with a buckled structure. Since its exfoliation from black phosphorus in 2014, phosphorene has attracted tremendous research interest both in terms of synthesis and fundamental research, as well as in potential applications. Recently, significant attention in phosphorene is motivated not only by research on its fundamental physical properties as a novel 2D semiconductor material, such as tunable bandgap, strong in-plane anisotropy, and high carrier mobility, but also by the study of its wide range of potential applications, such as electronic, optoelectronic, and spintronic devices, energy conversion and storage devices. However, a lot of avenues remain to be explored including the fundamental properties of phosphorene and its device applications. This review recalls the current state of the art of phosphorene and its derivatives, touching upon topics on structure, synthesis, characterization, properties, stability, and applications. The current needs and future opportunities for phosphorene are also discussed.

Interface Engineering with Dynamics-Mechanics Coupling for Highly Reactive and Reversible Aqueous Zinc-Ion Batteries

The practical application of AZIBs is hindered by problems such as dendrites and hydrogen evolution reactions caused by the thermodynamic instability of Zinc (Zn) metal. Modification of the Zn surface through interface engineering can effectively solve the above problems. Here, sulfonate-derivatized graphene-boronene nanosheets (G&B-S) composite interfacial layer is prepared to modulate the Zn plating/stripping and mitigates the side reactions with electrolyte through a simple and green electroplating method. Thanks to the electronegativity of the sulfonate groups, the G&B-S interface promotes a dendrite-free deposition behavior through a fast desolvation process and a uniform interfacial electric field mitigating the tip effect. Theoretical calculations and QCM-D experiments confirmed the fast dynamic mechanism and excellent mechanical properties of the G&B-S interfacial layer. By coupling the dynamics-mechanics action, the G&B-S@Zn symmetric battery is cycled for a long-term of 1900 h at a high current density of 5 mA cm-2 , with a low overpotential of ≈30 mV. Furthermore, when coupled with the LMO cathode, the LMO//G&B-S@Zn cell also exhibits excellent performance, indicating the durability of the G&B-S@Zn anode. Accordingly, this novel multifunctional interfacial layer offers a promising approach to significantly enhance the electrochemical performance of AZIBs.

Functionalizing nanophotonic structures with 2D van der Waals materials

The integration of two-dimensional (2D) van der Waals materials with nanostructures has triggered a wide spectrum of optical and optoelectronic applications. Photonic structures of conventional materials typically lack efficient reconfigurability or multifunctionality. Atomically thin 2D materials can thus generate new functionality and reconfigurability for a well-established library of photonic structures such as integrated waveguides, optical fibers, photonic crystals, and metasurfaces, to name a few. Meanwhile, the interaction between light and van der Waals materials can be drastically enhanced as well by leveraging micro-cavities or resonators with high optical confinement. The unique van der Waals surfaces of the 2D materials enable handiness in transfer and mixing with various prefabricated photonic templates with high degrees of freedom, functionalizing as the optical gain, modulation, sensing, or plasmonic media for diverse applications. Here, we review recent advances in synergizing 2D materials to nanophotonic structures for prototyping novel functionality or performance enhancements. Challenges in scalable 2D materials preparations and transfer, as well as emerging opportunities in integrating van der Waals building blocks beyond 2D materials are also discussed.

Renaissance of elemental phosphorus materials: properties, synthesis, and applications in sustainable energy and environment

The polymorphism of phosphorus-based materials has garnered much research interest, and the variable chemical bonding structures give rise to a variety of micro and nanostructures. Among the different types of materials containing phosphorus, elemental phosphorus materials (EPMs) constitute the foundation for the synthesis of related compounds. EPMs are experiencing a renaissance in the post-graphene era, thanks to recent advancements in the scaling-down of black phosphorus, amorphous red phosphorus, violet phosphorus, and fibrous phosphorus and consequently, diverse classes of low-dimensional sheets, ribbons, and dots of EPMs with intriguing properties have been produced. The nanostructured EPMs featuring tunable bandgaps, moderate carrier mobility, and excellent optical absorption have shown great potential in energy conversion, energy storage, and environmental remediation. It is thus important to have a good understanding of the differences and interrelationships among diverse EPMs, their intrinsic physical and chemical properties, the synthesis of specific structures, and the selection of suitable nanostructures of EPMs for particular applications. In this comprehensive review, we aim to provide an in-depth analysis and discussion of the fundamental physicochemical properties, synthesis, and applications of EPMs in the areas of energy conversion, energy storage, and environmental remediation. Our evaluations are based on recent literature on well-established phosphorus allotropes and theoretical predictions of new EPMs. The objective of this review is to enhance our comprehension of the characteristics of EPMs, keep abreast of recent advances, and provide guidance for future research of EPMs in the fields of chemistry and materials science.

Investigation of the interaction between the functionalized mesoporous silica nanocarriers and bovine serum albumin via multi-spectroscopy

It is well known that the physicochemical properties of nanocarriers, which are closely related to the surface modification of nanoparticles, have crucial impacts on their biological effects. Herein, the interaction between functionalized degradable dendritic mesoporous silica nanoparticles (DDMSNs) and bovine serum albumin (BSA) was investigated for probing into the nanocarriers' potential toxicity using multi-spectroscopy such as ultraviolet/visible (UV/Vis), synchronous fluorescence, Raman and circular dichroism (CD) spectroscopy. BSA, owing to its structural homology and high sequence similarity with HSA, was employed as the model protein to study the interactions with DDMSNs, amino-modified DDMSNs (DDMSNs-NH₂) and hyaluronic acid (HA) coated nanoparticles (DDMSNs-NH₂-HA). It was found that the static quenching behavior of DDMSNs-NH₂-HA to BSA was accompanied by an endothermic and hydrophobic force-driven thermodynamic process, which was confirmed by fluorescence quenching spectroscopic studies and thermodynamic analysis. Furthermore, the conformational variations of BSA upon interaction with nanocarriers were observed by combination of UV/Vis, synchronous fluorescence, Raman and CD spectroscopy. The microstructure of amino residues in BSA changed due to the existence of nanoparticles, for example, the amino residues and hydrophobic groups exposed to microenvironment and the alpha helix (α-helix) content of BSA decreased. Specially, through thermodynamic analysis, the diverse binding modes and driving forces between nanoparticles and BSA were discovered because of different surface modifications on DDMSNs, DDMSNs-NH₂ and DDMSNs-NH₂-HA. We believe that this work can promote the interpretation of mutual impact between nanoparticles and biomolecules, which will be in favor of predicting the biological toxicity of nano-DDS and engineering functionalized nanocarriers.

Tailoring Two-Dimensional Matter Using Strong Light-Matter Interactions

The shaping of matter into desired nanometric structures with on-demand functionalities can enhance the miniaturization of devices in nanotechnology. Herein, strong light-matter interaction was used as an optical lithographic tool to tailor two-dimensional (2D) matter into nanoscale architectures. We transformed 2D black phosphorus (BP) into ultrafine, well-defined, beyond-diffraction-limit nanostructures of ten times smaller size and a hundred times smaller spacing than the incident, femtosecond-pulsed light wavelength. Consequently, nanoribbons and nanocubes/cuboids scaling tens of nanometers were formed by the structured ablation along the extremely confined periodic light fields originating from modulation instability, the tailoring process of which was visualized in real time via light-coupled in situ transmission electron microscopy. The current findings on the controllable nanoscale shaping of BP will enable exotic physical phenomena and further advance the optical lithographic techniques for 2D materials.

Narrow Directed Black Phosphorus Nanoribbons Produced by A Reformative Mechanical Exfoliation Approach

Black phosphorus nanoribbons (PNRs) are ideal candidates for constructing electronic and optoelectronic devices owing to their unique structure and high bandgap tunability. However, the preparation of high-quality narrow PNRs aligned along the same direction is very challenging. Here, a reformative mechanical exfoliation approach combining tape and polydimethylsiloxane (PDMS) exfoliations to fabricate high-quality, narrow, and directed PNRs with smooth edges for the first time is developed. In this method, partially-exfoliated PNRs are first formed on thick black phosphorus (BP) flakes via the tape exfoliation and further peeled off to obtain separated PNRs via the PDMS exfoliation. The prepared PNRs have widths from a dozen to hundreds of nanometers (down to 15 nm) and a mean length of 18 µm. It is found that the PNRs can align along a same direction and the length directions of directed PNRs are along the zigzag direction. The formation of PNRs is attributed to that the BP prefers to be unzipped along the zigzag direction and has an appropriate magnitude of interaction force with the PDMS substrate. The fabricated PNR/MoS₂ heterojunction diode and PNR field-effect transistor exhibit good device performance. This work provides a new pathway to achieve high-quality, narrow, and directed PNRs for electronic and optoelectronic applications.

Quasi-one-dimensional phosphorene nanoribbons grown on silicon by space-confined chemical vapor transport

Phosphorene nanoribbons (PNRs) combine the flexibility of one-dimensional (1D) nanomaterials with the large specific surface area and the edge and electron confinement effects of two-dimensional (2D) nanomaterials. In spite of the substantial advances in bulk black phosphorus (BP) manufacturing, achieving PNRs without degradation is still a big challenge. In this work, we present a strategy for the space-confined chemical vapor transport synthesis of quasi-one-dimensional surface-passivated monocrystalline PNRs on a silicon substrate. The growth mechanism of the PNRs is proposed by combining experimental results and DFT calculations, indicating that the P₄ molecules can break, restructure, and epitaxially nucleate on the surface of the Au₃SnP₇ catalyst, and finally prefer to grow along the zigzag (ZZ) direction to form PNRs. The low gas flow rate and an appropriate phosphorus molecule concentration allow the growth of PNRs with structural integrity, which can be regulated by the amount of red phosphorus and the confined space.

Mechanistic investigation of cellulose regulating the morphology and photocatalytic activity of Al-doped ZnO

The morphology of metal oxide is a crucial factor for improving of catalysis properties. As a renewable and environmentally friendly biomass material, cellulose has been widely used to induce the morphology of semiconductors. The contributions of cellulose hydroxyl groups and spatial hindrance in tailoring Al doped ZnO (AZO) morphologies were investigated. The morphology of AZO could be gradually induced from flake-like to flower-like with the increase of cellulose hydroxyl content per unit volume. At the same time, the changes in spatial hindrance had no apparent effect on the morphology of AZO. So the cellulose hydroxyl groups that act to induce the in situ growth of AZO nanoparticles on cellulose substrates. The results further confirmed the strong interaction between cellulose hydroxyl groups and Zn²⁺. In addition, the photocatalytic activities of Al-doped ZnO/cellulose nanocomposites (AZOC) with different morphologies were evaluated by the degradation of bisphenol A (BPA). The high hydroxyl contents of cellulose substrates contributed to the growth of flower-like AZO with high light utilization and photocatalytic activity. This work proposed cleaner strategies to modify semiconductor morphologies for photocatalysis by regulating the content of cellulose hydroxyl contents.

Towards the Future of Polymeric Hybrids of Two-Dimensional Black Phosphorus or Phosphorene: From Energy to Biological Applications

With the advent of a new 2D nanomaterial, namely, black phosphorus (BP) or phosphorene, the scientific community is now dedicated to focusing on and exploring this 2D material offering elusive properties such as a higher carrier mobility, biocompatibility, thickness-dependent band gap, and optoelectronic characteristics that can be harnessed for multiple applications, e.g., nanofillers, energy storage devices, field effect transistors, in water disinfection, and in biomedical sciences. The hexagonal ring of phosphorus atoms in phosphorene is twisted slightly, unlike how it is in graphene. Its unique characteristics, such as a high carrier mobility, anisotropic nature, and biocompatibility, have attracted much attention and generated further scientific curiosity. However, despite these interesting features, the phosphorene or BP poses challenges and causes frustrations when it comes to its stability under ambient conditions and processability, and thus in order to overcome these hurdles, it must be conjugated or linked with the suitable and functional organic counter macromolecule in such a way that its properties are not compromised while providing a protection from air/water that can otherwise degrade it to oxides and acid. The resulting composites/hybrid system of phosphorene and a macromolecule, e.g., a polymer, can outperform and be exploited for the aforementioned applications. These assemblies of a polymer and phosphorene have the potential for shifting the paradigm from exhaustively used graphene to new commercialized products offering multiple applications.

Ultra-Narrow Phosphorene Nanoribbons Produced by Facile Electrochemical Process

Phosphorene nanoribbons (PNRs) have inspired strong research interests to explore their exciting properties that are associated with the unique two-dimensional (2D) structure of phosphorene as well as the additional quantum confinement of the nanoribbon morphology, providing new materials strategy for electronic and optoelectronic applications. Despite several important properties of PNRs, the production of these structures with narrow widths is still a great challenge. Here, a facile and straightforward approach to synthesize PNRs via an electrochemical process that utilize the anisotropic Na+ diffusion barrier in black phosphorus (BP) along the [001] zigzag direction against the [100] armchair direction, is reported. The produced PNRs display widths of good uniformity (10.3 ± 3.8 nm) observed by high-resolution transmission electron microscopy, and the suppressed B2g vibrational mode from Raman spectroscopy results. More interestingly, when used in field-effect transistors, synthesized bundles exhibit the n-type behavior, which is dramatically different from bulk BP flakes which are p-type. This work provides insights into a new synthesis approach of PNRs with confined widths, paving the way toward the development of phosphorene and other highly anisotropic nanoribbon materials for high-quality electronic applications.

Arsenic Monolayers Formed by Zero-Dimensional Tetrahedral Clusters and One-Dimensional Armchair Nanochains

One-dimensional (1D) arsenene nanostructures are predicted to host a variety of interesting physical properties including antiferromagnetic, semiconductor-semimetal transition and quantum spin Hall effect, which thus holds great promise for next-generation electronic and spintronic devices. Herein, we devised a surface template strategy in a combination with surface-catalyzed decomposition of molecular As₄ cluster toward the synthesis of the superlattice of ultranarrow armchair arsenic nanochains in a large domain on Au(111). In the low annealing temperature window, zero-dimensional As₄ nanoclusters are assembled into continuous films through intermolecular van der Waals and molecule-substrate interactions. At the elevated temperature, the subsequent surface-assisted decomposition of molecular As₄ nanoclusters leads to the formation of a periodic array of 1D armchair arsenic nanochains that form a (2 × 3) superstructure on the Au(111) surface. These ultranarrow armchair arsenic nanochains are predicted to have a small bandgap of ∼0.50 eV, in contrast to metallic zigzag chains. In addition, the Au-supported arsenic nanochains can be flipped to form a bilayer structure through tip indentation and manipulation, suggesting the possible transfer of these nanochains from the substrate. The successful realization of arsenic nanostructures is expected to advance low-dimensional physics and infrared optoelectronic nanodevices.

Rapid microwave-assisted synthesis of Ni2P nanosheets from black phosphorus

The high dielectric loss tangent value of black phosphorus nanosheets enables them to be selectively heated under microwave radiation to realize the in situ surface reaction of BP with Ni²⁺ to prepare thermodynamically unstable two-dimensional Ni₂P.

Ultratough Hydrogen-Bond-Bridged Phosphorene Films

The rapid development of flexible electronic devices, especially based on 2D materials, has triggered the demand for high-strength materials. Mono- or few-layer phosphorene with excellent electronic properties has attracted extensive attention. However, phosphorene is affected by its low Young's modulus when applied to flexible electronic devices. Here, a strategy via ion intercalation to significantly improve the mechanical properties of black phosphorus to generate hydrogen-bond-bridged phosphorene films with Young's modulus as high as 316 GPa is reported. This value is several times larger than the theoretical values of 166 GPa in the zigzag direction, 44 GPa in the armchair direction, and the averaged Young's modulus among all directions of 94 GPa. The impact of intercalation on mechanical properties is also explored. Experimental nanoindentation results obtained by atomic force microscopy indicate that the relationship between the ratio of intercalated ions to phosphorus atoms and the corresponding Young's modulus satisfies the formula E = e a e - [ ln ( x ) + b ] 2 c ( 0 < x ≤ 1.80 ) \[E{\bm{ = }}{e^{a{e^{\frac{{{\bm{ - }}{{[\ln (x){\bm{ + }}b]}^2}}}{c}}}}}(0{\bm{ &lt; }}x{\bm{ \le }}1.80)\] . Furthermore, a flexible NO₂ gas sensor device based on this ultratough material presents excellent performance, even after 10 000 bending cycles. The results provide new insight into the potential for practical applications of black phosphorus devices.

Atomically Sharp, Closed Bilayer Phosphorene Edges by Self-Passivation

Two-dimensional crystals' edge structures not only influence their overall properties but also dictate their formation due to edge-mediated synthesis and etching processes. Edges must be carefully examined because they often display complex, unexpected features at the atomic scale, such as reconstruction, functionalization, and uncontrolled contamination. Here, we examine atomic-scale edge structures and uncover reconstruction behavior in bilayer phosphorene. We use in situ transmission electron microscopy (TEM) of phosphorene/graphene specimens at elevated temperatures to minimize surface contamination and reduce e-beam damage, allowing us to observe intrinsic edge configurations. The bilayer zigzag (ZZ) edge was found to be the most stable edge configuration under e-beam irradiation. Through first-principles calculations and TEM image analysis under various tilting and defocus conditions, we find that bilayer ZZ edges undergo edge reconstruction and so acquire closed, self-passivated edge configurations. The extremely low formation energy of the closed bilayer ZZ edge and its high stability against e-beam irradiation are confirmed by first-principles calculations. Moreover, we fabricate bilayer phosphorene nanoribbons with atomically sharp closed ZZ edges. The identified bilayer ZZ edges will aid in the fundamental understanding of the synthesis, degradation, reconstruction, and applications of phosphorene and related structures.

Enhanced linear dichroism of flattened-edge black phosphorus nanoribbons

Black phosphorus is a material with an intrinsic anisotropy in electronic and optical properties due to its puckered honeycomb lattice. Optical absorption is different for incident light with linear polarization in the armchair and zigzag directions (linear dichroism). These directions are also used in the cuts of materials to create black phosphorus nanoribbons. Edges of nanoribbons usually have small reconstruction effects, with minor electronic effects. Here, we show a reconstruction of the armchair edge that introduces a new valence band, which flattens the puckered lattice and increases the linear dichroism extrinsically in the visible spectrum. This enhancement in linear dichroism is explained by the polarization selection rule, which considers the parity of the wave function to a reflection plane. The flattened-edge reconstruction originates from the inversion of chirality of the P atoms at the edges and significantly alters the entire optical absorption of the material. The flattened edges have potential applications in pseudospintronics, photodetectors and might provide new functionalities in optoelectronic and photonic devices.

Phosphorene Nanoribbon-Augmented Optoelectronics for Enhanced Hole Extraction

Phosphorene nanoribbons (PNRs) have been widely predicted to exhibit a range of superlative functional properties; however, because they have only recently been isolated, these properties are yet to be shown to translate to improved performance in any application. PNRs show particular promise for optoelectronics, given their predicted high exciton binding energies, tunable bandgaps, and ultrahigh hole mobilities. Here, we verify the theorized enhanced hole mobility in both solar cells and space-charge-limited-current devices, demonstrating the potential for PNRs improving hole extraction in universal optoelectronic applications. Specifically, PNRs are demonstrated to act as an effective charge-selective interlayer by enhancing hole extraction from polycrystalline methylammonium lead iodide (MAPbI₃) perovskite to the poly(triarylamine) semiconductor. Introducing PNRs at the hole-transport/MAPbI₃ interface achieves fill factors above 0.83 and efficiencies exceeding 21% for planar p-i-n (inverted) perovskite solar cells (PSCs). Such efficiencies are typically only reported for single-crystalline MAPbI₃-based inverted PSCs. Methylammonium-free PSCs also benefit from a PNR interlayer, verifying applicability to architectures incorporating mixed perovskite absorber layers. Device photoluminescence and transient absorption spectroscopy are used to demonstrate that the presence of the PNRs drives more effective carrier extraction. Isolation of the PNRs in space-charge-limited-current hole-only devices improves both hole mobility and conductivity, demonstrating applicability beyond PSCs. This work provides primary experimental evidence that the predicted superlative functional properties of PNRs indeed translate to improved optoelectronic performance.

Borophene: Two-dimensional Boron Monolayer: Synthesis, Properties, and Potential Applications

Borophene, a monolayer of boron, has risen as a new exciting two-dimensional (2D) material having extraordinary properties, including anisotropic metallic behavior and flexible (orientation-dependent) mechanical and optical properties. This review summarizes the current progress in the synthesis of borophene on various metal substrates, including Ag(110), Ag(100), Au(111), Ir(111), Al(111), and Cu(111), as well as heterostructuring of borophene. In addition, it discusses the mechanical, thermal, magnetic, electronic, optical, and superconducting properties of borophene and the effects of elemental doping, defects, and applied mechanical strains on these properties. Furthermore, the promising potential applications of borophene for gas sensing, energy storage and conversion, gas capture and storage applications, and possible tuning of the material performance in these applications through doping, formation of defects, and heterostructures are illustrated based on available theoretical studies. Finally, research and application challenges and the outlook of the whole borophene's field are given.

Chemical Vapor Transport Route toward Black Phosphorus Nanobelts and Nanoribbons

Chemical vapor transport (CVT) method is widely used for bulk black phosphorus (BP) fabrication. In this work, we demonstrate that CVT provides a route for the fabrication of BP nanoribbons and nanobelts. This method consists of a two-step procedure, including initial BP column growth using the CVT technique, followed by ultrasonic treatment and centrifugation. The obtained nanostructures preserve BP column dimensions, forming ultralong ribbon-like structures with the length to the width aspect ratio of up to 500. Computational modeling of the growth mechanism of a BP flake is also presented in support of the observed columnar growth. Calculation of the average energy of the molecule in the asymmetric flakes shows that the growth of the structure in the zigzag direction is more energetically favorable than in the armchair direction.

Facile Production of Phosphorene Nanoribbons towards Application in Lithium Metal Battery

Like phosphorene, phosphorene nanoribbon (PNR) promises exotic properties but unzipping phosphorene into edge-defined PNR is non-trivial because of uncontrolled cutting of phosphorene along random directions. Here a facile electrochemical strategy to fabricate zigzag-edged PNRs in high yield (>80%) is reported. The presence of chemically active zigzag edges in PNR allows it to spontaneously react with Li to form a Li⁺ ion conducting Li₃ P phase, which can be used as a protective layer on Li metal anode in lithium metal batteries (LMBs). PNR protective layer prevents the parasitic reaction between lithium metal and electrolyte and promotes Li⁺ ion diffusion kinetics, enabling homogenous Li⁺ ion flux and long-time cycling stability up to 1100 h at a current density of 1 mA cm^-2 . LiFePO₄ |PNR-Li full-cell batteries with an areal capacity of 2 mAh cm^-2 , a lean electrolyte (20 µl mAh^-1 ) and a negative/positive (N/P) electrodes ratio of 3.5 can be stably cycled over 100 cycles.

Flat epitaxial quasi-1D phosphorene chains

The emergence of peculiar phenomena in 1D phosphorene chains (P chains) has been proposed in theoretical studies, notably the Stark and Seebeck effects, room temperature magnetism, and topological phase transitions. Attempts so far to fabricate P chains, using the top-down approach starting from a few layers of bulk black phosphorus, have failed to produce reliably precise control of P chains. We show that molecular beam epitaxy gives a controllable bottom-up approach to grow atomically thin, crystalline 1D flat P chains on a Ag(111) substrate. Scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and density functional theory calculations reveal that the armchair-shaped chains are semiconducting with an intrinsic 1.80 ± 0.20 eV band gap. This could make these P chains an ideal material for opto-electronic devices.