An overview of the optical properties and applications of black phosphorus

Electronic and optical properties of the buckled and puckered phases of phosphorene and arsenene

Using first-principles calculations, we have investigated the structural, electronic, and optical properties of phosphorene and arsenene, group V two-dimensional materials. They have attracted the scientific community's interest due to their possible applications in electronics and optoelectronics. Since phosphorene and arsenene are not planar monolayers, two types of structures were considered for each system: puckered and buckled arrangements. Computations of band gap were performed within the GW approach to overcome the underestimation given by standard DFT and predict trustable band gap values in good agreement with experimental measurements. Our calculated electronic band gaps lie in the range from near-infrared to visible light, suggesting potential applications in optoelectronics devices. The computed electronic band gaps are 2.95 eV and 1.83 eV for blue and black phosphorene systems. On the other hand, the values for buckled and puckered arsenene are 2.56 eV and 1.51 eV, respectively. Moreover, the study of the optical properties has been dealt by computing the dielectric function imaginary part, which was obtained using the Bethe-Salpeter approach. The use of this technique allows the consideration of excitonic effects. Results indicate strong exciton binding energies of 830 meV for blue phosphorene, 540 meV for black phosphorene, 690 meV for buckled arsenene, and 484 meV for puckered arsenene. The results of our study suggest the possibility of using these materials in electronic and optoelectronic devices.

Self-Bending Behavior and Varying Bending Stiffness of Black Phosphorus/Molybdenum Disulfide (BP/MoS2) Heterostructure

Vertically-stacked black phosphorus/molybdenum disulfide (BP/MoS₂) heterostructures have broad prospects in flexible electronics. Bending is a common and highly concerned deformation for these flexible devices. However, the discrepancy in structures and properties among the components of 2D heterostructures often induces complex bending deformations. Here, the bending behaviors of BP, MoS₂ and BP/MoS₂ are investigated based on a molecular dynamics simulation. Compared with the constant bending stiffness of individual BP and MoS₂, that of BP/MoS₂ varies with the bending angle. Notably, a self-bending configuration induced by the lattice mismatch and size difference is found in BP/MoS₂. The corresponding self-bending amplitude depends on the degree of size difference of each component and the "soft/hard" competition between them. Moreover, the size difference leads to a weakened bending stiffness, which is ascribed to the reduction in interlayer interaction. A prediction formula is proposed to evaluate the bending stiffness of BP/MoS₂ with the size difference. This finding reveals novel ways for regulating the bending properties of 2D heterostructures, including the bending angle, characteristic size and stacking order. It offers an effective strategy for designing flexible devices with tunable bending performance.

Engineering van der Waals Materials for Advanced Metaphotonics

The outstanding chemical and physical properties of 2D materials, together with their atomically thin nature, make them ideal candidates for metaphotonic device integration and construction, which requires deep subwavelength light-matter interaction to achieve optical functionalities beyond conventional optical phenomena observed in naturally available materials. In addition to their intrinsic properties, the possibility to further manipulate the properties of 2D materials via chemical or physical engineering dramatically enhances their capability, evoking new science on light-matter interaction, leading to leaped performance of existing functional devices and giving birth to new metaphotonic devices that were unattainable previously. Comprehensive understanding of the intrinsic properties of 2D materials, approaches and capabilities for chemical and physical engineering methods, the resulting property modifications and novel functionalities, and applications of metaphotonic devices are provided in this review. Through reviewing the detailed progress in each aspect and the state-of-the-art achievement, insightful analyses of the outstanding challenges and future directions are elucidated in this cross-disciplinary comprehensive review with the aim to provide an overall development picture in the field of 2D material metaphotonics and promote rapid progress in this fast emerging and prosperous field.

Room-Temperature Infrared Photodetectors with Zero-Dimensional and New Two-Dimensional Materials

Infrared photodetectors have received much attention for several decades due to their broad applications in the military, science, and daily life. However, for achieving an ideal signal-to-noise ratio and a very fast response, cooling is necessary in those devices, which makes them bulky and costly. Thus, room-temperature infrared photodetectors have emerged as a hot research direction. Novel low-dimensional materials with their easy fabrication and excellent photoelectronic properties provide a possible solution for room-temperature infrared photodetectors. This review aims to summarize the preparation methods and characterization of several low-dimensional materials (PbS, PbSe and HgTe, new two-dimensional materials) with great concern and the room-temperature infrared photodetectors based on them.

In situ integration of Te/Si 2D/3D heterojunction photodetectors toward UV-vis-IR ultra-broadband photoelectric technologies

Over the past decade, 2D elemental semiconductors have emerged as an ever-increasingly important group in the 2D material family due to their simple crystal structures and compositions, and versatile physical properties. Taking advantage of the relatively small bandgap, outstanding carrier mobility, high air-stability and strong interactions with light, 2D tellurium (Te) has emerged as a compelling candidate for use in ultra-broadband photoelectric technologies. In this study, high-quality centimeter-scale Te nanofilms have been successfully produced by exploiting pulsed-laser deposition (PLD). By performing deposition on pre-patterned SiO₂/Si substrates, a Te/Si 2D/3D heterojunction array is formed in situ. To our delight, taking advantage of the relatively small bandgap of Te, the Te/Si photodetectors demonstrate an ultra-broadband photoresponse from ultraviolet to near-infrared (370.6 nm to 2240 nm), enabling them to serve as important alternatives to conventional 2D materials such as MoS₂. In addition, an outstanding on/off ratio of ∼10⁸ and a fast response rate (a response/recovery time of 3.7 ms/4.4 ms) are achieved, which is associated with the large band offset and strong interfacial built-in electric field that contribute to suppressing the dark current and separating photocarriers. Beyond these, a 35 × 35 matrix array has been successfully constructed, where the devices exhibit comparable properties, with a production yield of 100% for 100 randomly tested devices. The average responsivity, external quantum efficiency and detectivity reach 249 A W^-1, 76 350% and 1.15 × 10¹¹ Jones, respectively, making the Te/Si devices among the best-performing 2D/3D heterojunction photodetectors. On the whole, this study has established that PLD is a promising technique for producing high-quality Te nanofilms with good scalability, and the Te/Si 2D/3D heterojunction provides a promising platform for implementing high-performance ultra-broadband photoelectronic technologies.

Size-dependent flame retardancy of black phosphorus nanosheets

Two-dimensional black phosphorus (BP) nanosheets are potential flame-retardant nano-additives. Herein, the effects of the size of BP nanosheets embedded in epoxy resin (EP) on flame retardancy are studied. BP nanosheets with four different sizes are synthesized from bulk BP by different exfoliation methods including solid ball milling, liquid ball milling, ultrasonic liquid exfoliation, and electrochemical exfoliation (samples are designated as sb-BP, lb-BP, us-BP, and ec-BP, respectively). lb-BP exhibits the best dispersion in the EP matrix, and the lb-BP/EP composite shows the best flame-retardancy properties among the four BP/EP composites. Compared to bare EP, lb-BP/EP shows obvious improvements including the reduction in the heat release peak rate by 34.4%, total heat release by 27.0%, peak of smoke production rate by 69.2%, and total production of carbon monoxide by 50.8%. The mechanistic study reveals that lb-BP serves as a barrier and carbonization catalyst to delay combustion. These results confirm the size dependence of flame-retardancy properties of BP nanosheets and the new knowledge provides insights into the size dependent effects of other two-dimensional materials.

Atomically Thin 2D Photocatalysts for Boosted H2 Production from the perspective of Transient Absorption Spectroscopy

Excited state photophysical processes play the most important role in deciding the efficiency of any photonic applications like solar light driven H2 evolution, which is considered to be the next...

Black Phosphorus, an Emerging Versatile Nanoplatform for Cancer Immunotherapy

Black phosphorus (BP) is one of the emerging versatile nanomaterials with outstanding biocompatibility and biodegradability, exhibiting great potential as a promising inorganic nanomaterial in the biomedical field. BP nanomaterials possess excellent ability for valid bio-conjugation and molecular loading in anticancer therapy. Generally, BP nanomaterials can be classified into BP nanosheets (BPNSs) and BP quantum dots (BPQDs), both of which can be synthesized through various preparation routes. In addition, BP nanomaterials can be applied as photothermal agents (PTA) for the photothermal therapy (PTT) due to their high photothermal conversion efficiency and larger extinction coefficients. The generated local hyperpyrexia leads to thermal elimination of tumor. Besides, BP nanomaterials are capable of producing singlet oxygen, which enable its application as a photosensitizer for photodynamic therapy (PDT). Moreover, BP nanomaterials can be oxidized and degraded to nontoxic phosphonates and phosphate under physiological conditions, improving their safety as a nano drug carrier in cancer therapy. Recently, it has been reported that BP-based PTT is capable of activating immune responses and alleviating the immunosuppressive tumor microenvironment by detection of T lymphocytes and various immunocytokines, indicating that BP-based nanocomposites not only serve as effective PTAs to ablate large solid tumors but also function as an immunomodulation agent to eliminate discrete tumorlets. Therefore, BP-mediated immunotherapy would provide more possibilities for synergistic cancer treatment.

Light-Driven Self-Oscillating Actuators with Phototactic Locomotion Based on Black Phosphorus Heterostructure

Developing self-oscillating soft actuators that enable autonomous, continuous, and directional locomotion is significant in biomimetic soft robotics fields, but remains great challenging. Here, an untethered soft photoactuators based on covalently-bridged black phosphorus-carbon nanotubes heterostructure with self-oscillation and phototactic locomotion under constant light irradiation is designed. Owing to the good photothermal effect of black phosphorus heterostructure and thermal deformation of the actuator components, the new actuator assembled by heterostructured black phosphorus, polymer and paper produces light-driven reversible deformation with fast and large response. By using this actuator as mechanical power and designing a robot configuration with self-feedback loop to generate self-oscillation, an inchworm-like actuator that can crawl autonomously towards the light source is constructed. Moreover, due to the anisotropy and tailorability of the actuator, an artificial crab robot that can simulate the sideways locomotion of crabs and simultaneously change color under light irradiation is also realized.

Double-Layer Nitrogen-Rich Two-Dimensional Anionic Uranyl-Organic Framework for Cation Dye Capture and Catalytic Fixation of Carbon Dioxide

A novel two-dimensional double-layer anionic uranyl-organic framework, U-TBPCA {[NH₂(CH₃)₂][(UO₂)(TBPCA)], where H₃TBPCA = 4,4',4″-s-triazine-1,3,5-triyltripamino-methylene-cyclohexane-carboxylate}, with abundant active sites and stability was obtained by assembling UO₂(NO₃)₂·6H₂O and a triazine tricarboxylate linker, TBPCA^3-. Due to the flexibility of the ligand and diverse coordination modes between carboxyl groups and uranyl ions, U-TBPCA exhibits an intriguing topological structure and steric configuration. This double-layer anionic uranyl-organic framework is highly porous and can be used for selective adsorption of cationic dyes. Due to the presence of high-density metal ions and basic -NH- groups, U-TBPCA acts as an effective heterogeneous catalyst for the cycloaddition reaction of carbon dioxide with epoxy compounds. Moreover, the various modes of coordination between the tricarboxylic ligand and uranyl ion were studied by density functional theory calculations, and several simplified models were established to probe the influence of hydrogen bonding between carbon dioxide and U-TBPCA on the ability of U-TBPCA to bind carbon dioxide. This work should aid in improving our understanding of the coordination behavior of uranyl ion as well as the development and utilization of new actinide materials.

Black Phosphorus Nanostructure Based Highly Sensitive and Selective Surface Plasmon Resonance Sensor for Biological and Chemical Sensing: A Review

Surface plasmon resonance (SPR) is an attention-grabbing sensor type, which offers the sensitive and selective detection of biomolecules and environmentally toxic substances. Notably, the SPR sensor gives excellent rewards including real-time, in-situ, and label-free measuring capability as compared to existing sensing technologies. As a result, these noteworthy merits of the SPR sensor make it straightforward to investigate the molecular events and chemical/gas molecule interaction. Unfortunately, there are different binding events including smaller molecular mass substances, which cannot be detected at the SPR sensor. Accordingly, this downside of the SPR sensor eventually led to the design and implementation of new approaches for sensitivity and selectivity improvement for sensing applications in different fields. Recently, the black phosphorus (BP) derived 2 D nanomaterial is stand out as a distinctive nanostructure in comparison to recently reported other 2 D nanomaterials. Substantial and functional characteristics of BP including simplicity of operation, optical properties, high carrier mobility, stronger immobilization of receptors and biomolecules, electronic bridging playing important role in the highly selective and sensitive assessment of analyte. The designed BP nanostructures are mostly serving to accelerate the plasmon material signals followed by improved molecular sensing that may due to 40-times faster-sensing responses of BP nanostructure than reported 2 D nanomaterials. Therefore, the present review article sheds light on the latest significant advances in biological and toxic gas detection through 2D BP nanostructures based SPR sensors. In the future, this review will facilitate detailed insights into the development of BP-based groundbreaking frameworks for highly sensitive and selective recognition of biomolecules and environmental pollutants.

Fibrous Phase Red Phosphorene as a New Photocatalyst for Carbon Dioxide Reduction and Hydrogen Evolution

2D photocatalysts are one of the hottest issues in energy and material science. In the field of photocatalysis, a 2D material with an appropriate bandgap of 1.3 to 2.0 eV is desirable. Herein, a new kind of fibrous phase red phosphorene with a bandgap between 1.43 to 1.54 eV is obtained. This is much better than black phosphorus because the bandgap of black P depends of its layer number. The black P needs to be as thin as 1-2 layers for suitable band diagram, which is difficult to control. The fibrous red phosphorene is first used for photocatalytic CO₂ reduction, and its activity is superior to the majority of mainstream photocatalysts and reaches a record-high value among phosphorus. Besides, its activity in hydrogen evolution is higher than most of the phosphorus photocatalysts. The intralayer charge transfer is much easier than interlayer transfer. The mobility of electron and hole along the phosphorene plane is about 20 times higher than that perpendicular to different layers. The activity sites is at region between the two P[21] chains. These regions are easy to be exposed for fibrous phase phosphorene, making it to exhibit high activity.

2D phosphorene nanosheets, quantum dots, nanoribbons: synthesis and biomedical applications

Phosphorene, also known as black phosphorus (BP), is a two-dimensional (2D) material that has gained significant attention in several areas of current research. Its unique properties such as outstanding surface activity, an adjustable bandgap width, favorable on/off current ratios, infrared-light responsiveness, good biocompatibility, and fast biodegradation differentiate this material from other two-dimensional materials. The application of BP in the biomedical field has been rapidly emerging over the past few years. This article aimed to provide a comprehensive review of the recent progress on the unique properties and extensive medical applications for BP in bone, nerve, skin, kidney, cancer, and biosensing related treatment. The details of applications of BP in these fields were summarized and discussed.

Two-Dimensional Platinum Diselenide: Synthesis, Emerging Applications, and Future Challenges

In recent years, emerging two-dimensional (2D) platinum diselenide (PtSe2) has quickly attracted the attention of the research community due to its novel physical and chemical properties. For the past few years, increasing research achievements on 2D PtSe2 have been reported toward the fundamental science and various potential applications of PtSe2. In this review, the properties and structure characteristics of 2D PtSe2 are discussed at first. Then, the recent advances in synthesis of PtSe2 as well as their applications are reviewed. At last, potential perspectives in exploring the application of 2D PtSe2 are reviewed.