Layered Black Phosphorus Research Articles

Electronic rotons and Wigner crystallites in a two-dimensional dipole liquid.

A key concept proposed by Landau to explain superfluid liquid helium is the elementary excitation of quantum particles called rotons1-8. The irregular arrangement of atoms in a liquid leads to the aperiodic dispersion of rotons, which played a pivotal role in understanding fractional quantum Hall liquids (magneto-rotons)9,10 and the supersolidity of Bose-Einstein condensates11-13. Even for a two-dimensional electron or dipole liquid, in the absence of a magnetic field, the repulsive interactions have been predicted to form a roton minimum14-19, which can be used to trace the transition to Wigner crystals20-24 and superconductivity25-27, although this has not yet been observed. Here, we report the observation of such electronic rotons in a two-dimensional dipole liquid of alkali-metal ions donating electrons to surface layers of black phosphorus. Our data reveal the striking aperiodic dispersion of rotons, which is characterized by a local minimum of energy at finite momentum. As the density of dipoles decreases so that interactions dominate over the kinetic energy, the roton gap reduces to 0, as in a crystal, signalling Wigner crystallization. Our model shows the importance of short-range order arising from repulsion between dipoles, which can be viewed as the formation of Wigner crystallites (bubbles or stripes) floating in the sea of a Fermi liquid. Our results reveal that the primary origin of electronic rotons (and the pseudogap) is strong correlations.

Preparation and Characterization of Black Phosphene/Titanium Dioxide Composite Nanomaterials by Liquid-Stripping and Solution Mixing Method

In this study, black phosphorus (BP) was prepared via the high-energy ball milling method, and two-dimensional (2D) BP was further fabricated using the liquid-phase stripping approach. Nano TiO2 was synthesized via the sol-gel method, and it was combined with black phosphene through N, N-dimethylformamide (DMF) medium by a straightforward solution mixing process to produce BP/ TiO2 composite photocatalyst. Subsequently, spectrophotometric analysis, X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) were conducted. The band gap of BP was calculated using the Tauc plot method. The results revealed that the values are 1.06 eV and 1.23 eV, corresponding to the band gap emissions of four-and three-layer BP band gap emission, indicating the successful preparation of few layers of black phosphorus. The HRTEM analysis demonstrated that the BP/ TiO2 composite photocatalyst formed a relatively stable crystalline state.

Propagation properties of plasma-filled parallel plate waveguide (PPWG) surrounded by black phosphorus (BP) layers

Propagation properties of plasma-filled PPWG surrounded by BP layers are explored in this research. Field equations are derived with the help of Maxwell’s equations. Boundary conditions x = d / 2 and x = − d / 2 are applied to obtain the characteristic equation for transverse magnetic (TM) mode. The influence of plasma frequency, electron doping, number of BP layers and core width on effective mode index are analyzed for armchair and zigzag conductivity of BP in the THz frequency range. It is concluded that armchair conductivity has a higher effective mode index compared to the zigzag conductivity of BP for the proposed waveguide structure. The presented results may have potential applications to fabricate black phosphorus-based nanophotonic devices in the THz frequency range.

Nanosensors Based on Bimetallic Plasmonic Layer and Black Phosphorus: Application to Urine Glucose Detection.

This paper presents a new biosensor design based on the Kretschmann configuration, for the detection of analytes at different refractive indices. Our studied design consists of a TiO2/SiO2 bi-layer sandwiched between a BK7 prism and a bimetallic layer of Ag/Au plasmonic materials, covered by a layer of black phosphorus placed below the analyte-containing detection medium. The different layers of our structure and analyte detection were optimized using the angular interrogation method. High performance was achieved, with a sensitivity of 240 deg/RIU and a quality factor of 34.7 RIU-1. This biosensor can detect analytes with a wide refractive index range between 1.330 and 1.347, such as glucose detection in urine samples using a refractive index variation of 10-3. This capability offers a wide range of applications for biomedical and biochemical detection and selectivity.

Temperature dependent Raman spectroscopy and sensing performance of 2D black phosphorus.

Temperature is an important parameter to be monitored in new wearable electronic devices. Layered black phosphorus (BP) has inherent good thermal stability and semiconductor properties and has a promising application as a temperature sensing layer. Here, we investigate the temperature sensing properties of BP, using in situ Raman spectroscopy and x-ray diffraction techniques. Flexible sensors are constructed, and temperature response is investigated in the range of 6-38 °C. The prospect application for monitoring the temperature of human body parts is demonstrated. The results show that the BP-based temperature sensors demonstrate good negative temperature coefficient characteristics and display high sensitivity and reproducible sensing performance. The temperature-dependent performance suggests the feasibility of BP as a sensitive layer in a wide temperature range. This work paves the way for exploring new applications of amazing layered materials, such as BP, in wearable electronic devices.

Full phonon dispersion along the stacking direction in nanoscale van der Waals materials by picosecond acoustics

Phonon dispersion in crystals determines many important material properties, but its measurement usually requires large-scale facilities and is limited to bulk samples. Here, we demonstrate the measurement of full phonon dispersion along the stacking direction in nanoscale systems by using picosecond acoustics. A heterostructure sample was prepared consisting of layers of hexagonal boron nitride (hBN) sandwiching a thin layer of black phosphorus (BP), within which a strain pulse was generated by photoexcitation and observed with an optical probe in the BP layer. The strain pulse traverses to the few nanometer thick hBN layers, where it propagates to the edge and echoes back, like acoustic waves in Newton’s cradle. The echoes returning to the BP layer provide information on the frequency-dependent time-of-flight and group velocity dispersion of the sample system. The microscopic origin of the photoinduced strain pulse generation and its propagation is revealed from first principles. Phonon frequency combs observed in the Fourier transform spectrum confirm the strain wave round trips and demonstrate the feasibility of determining group velocity dispersion through photoacoustics.

Epoxy Polymers Containing Metal–Organic Framework-Derived Layered Double Hydroxide and Black Phosphorus for Fire Resistance, Smoke Suppression, and Wear Resistance

Epoxy Polymers Containing Metal–Organic Framework-Derived Layered Double Hydroxide and Black Phosphorus for Fire Resistance, Smoke Suppression, and Wear Resistance

Waveguide-integrated van der Waals heterostructure photodetector on a lithium niobate on insulator platform.

Lithium niobate (LN) photonics has gained significant interest for their distinct material properties. However, achieving monolithically integrated photodetectors on lithium niobate on an insulator (LNOI) platform for communication wavelengths remains a challenge due to the large bandgap and extremely low electrical conductivity of LN material. A two-dimensional (2D) material photodetector is an ideal solution for LNOI photonics with a strong light-matter interaction and simple integration technique. In this work, a van der Waals heterostructure photodiode composed of a p-type black phosphorus layer and an n-type MoS2 layer is successfully demonstrated for photodetection at communication wavelengths on a LNOI platform. The LNOI waveguide-integrated BP-MoS2 photodetector exhibits a dark current as low as 0.21 nA and an on/off ratio exceeding 200 under zero voltage bias with an incident power of 13.93 µW. A responsivity as high as 1.46 A/W is achieved at -1 V bias with a reasonable dark current around 2.33 µA. With the advantages of high responsivity, low dark current, and simple fabrication process, it is promising for the monolithically integrated photodetector application for LNOI photonic platforms at communication wavelengths.

Tunable optical devices with multiple plasmon-induced transparency based on graphene-black phosphorus hybrid metasurface

In this research, we propose a simple and novel graphene-black phosphorus composite structure. Through the coupling mechanism of bright–bright mode, four layers of graphene and one layer of black phosphorus produce a quadruple plasmon-induced transparency (PIT) effect. The response of the proposed structure to the angle of polarized light is investigated, and it is found that the sensitivities of graphene and black phosphorus to the polarization angle of light are different. In addition, the dynamic regulation of PIT by the Fermi level of graphene and the carrier concentration of black phosphorus are discussed. The modulation depths of the fivefold optical switching are 96%, 99%, 87%, 93%, and 80%, respectively. The quadruple PIT can also be converted into triple PIT, in which single, dual, or triple optical switching are realized, respectively. Finally, with the change in the refractive index of the environment medium, the sensitivity response of the proposed structure is as high as 4.790 THz⋅RIU−1. We believe that this research will contribute to the development of optical switches, modulators, and sensors.

Anomalous strain dependence of phononic friction between black phosphorus layers

This study reveals unexpected strain-dependent friction, when applied strain to one of two layers of relatively sliding black phosphorus, friction is likely to exhibit characteristic rise and subsequent fall, forming a distinct friction peak. Existence and location of such peak are closely related to magnitude of normal loads. Interfacial pinning is weak at lower normal load, matched dissipation channels are easy to be destroyed, resulting in a monotonic decrease of friction. At higher normal load, tip is also pulled apart once applying a small strain to substrate, stored deformation energy leads to greater energy dissipation than at strain of zero, causing friction to decrease non-monotonically. Moreover, ability of sliding layers to withstand strain decreases with increasing normal loads or temperatures.

Phonon energy dissipation in friction between black phosphorus layers.

Herein, we employ molecular dynamics simulations to decode the friction properties and phonon energy dissipation between black phosphorus layers. The observations reveal the influence of three factors, temperature, velocity, and normal load, on the friction force of monolayer/bilayer black phosphorus. Specifically, friction is negatively correlated with layer thickness and temperature, and positively correlated with velocity and normal load. The change in friction force is further explained in terms of frictional energy dissipation, and supplemented by the height of potential barriers as well as the number of excited phonons. From the phonon spectrum analysis, the phonon number at the contact interface is found to be higher than that at the non-contact interface. This is due to the larger distance of the contact interface atoms deviate from their equilibrium positions, resulting in higher total energy generated by more intense oscillations, and therefore contributes greater to friction.

High-responsivity, high-detectivity, broadband infrared photodetector based on MoS2/BP/MoS2 junction field-effect transistor

Sensitivity stands as a critical figure of merit in assessing the performance of a photodetector and can be characterized by two distinct parameters: responsivity or detectivity. Simultaneous optimization of these two parameters is essential to ensure the applicability of a single detector across various scenarios, yet it remains a persistent challenge for mid-infrared photodetector. Here, we demonstrate that the construction of a photoconductive detector based on a MoS2/BP/MoS2 npn junction field-effect transistor configuration can effectively balance the tradeoffs between photoresponsivity and detectivity. In this device, the black phosphorus layer serves as the channel, while the top and bottom MoS2 layers act as photogates to boost the photocurrent. Consequently, a high-performance room-temperature-operating mid-infrared photodetector with a responsivity and detectivity reaching 9.04 A W−1 and 5.36 × 109 cm Hz1/2 W−1 (1550 nm), and 7.25 A W−1 and 4.29 × 109 cm Hz1/2 W−1 (3600 nm) is achieved. Our study provides an alternative structural design, enabling the applications of mid-infrared photodetectors across multiple scenarios.

Evolution of Graphene Dirac Fermions in Electric Double‐Layer Transistors with a Soft Barrier

AbstractThe interface and dielectric environment of graphene transistors are of great importance to commercial circuit integrations. The tangling bond in oxide‐based dielectric severely lagged the carrier mobility while the 2D dielectric layer (for instance, hexagonal boron nitride) unavoidably hastened complicated condensed physics even at room temperature. Herein, multilayer black phosphorus (BP) a versatile and widely‐tunable dielectric candidate for manifesting graphene fermions is demonstrated. Because of hetero‐interfacial charge redistributions, a vertical electric double‐layer between the bottom BP layer and top graphene spontaneously forms with the central BP layer as a soft barrier. Under dual‐gate modulation, abnormal step‐like evolution of Dirac fermions and charge‐transfer quantum Hall effect arises while the intrinsic Dirac behavior of graphene is preserved, ascribing to the gate‐tunable charge redistributions of dielectric BP layer. Moreover, the electric double‐layer transistors apply equally well to bilayer graphene with similar Dirac behavior but an enhanced interfacial charge interference. The findings not only create a new avenue to manipulate the fermions by assembling graphene with narrow‐gapped 2D layered materials but also promote electric double‐layer transistors as a new build block to design multifunctional devices.

Metal‐free two‐dimensional phosphorene‐based electrocatalyst with covalent P–N heterointerfacial reconstruction for electrolyte‐lean lithium–sulfur batteries

AbstractThe use of lithium–sulfur batteries under high sulfur loading and low electrolyte concentrations is severely restricted by the detrimental shuttling behavior of polysulfides and the sluggish kinetics in redox processes. Two‐dimensional (2D) few layered black phosphorus with fully exposed atoms and high sulfur affinity can be potential lithium–sulfur battery electrocatalysts, which, however, have limitations of restricted catalytic activity and poor electrochemical/chemical stability. To resolve these issues, we developed a multifunctional metal‐free catalyst by covalently bonding few layered black phosphorus nanosheets with nitrogen‐doped carbon‐coated multiwalled carbon nanotubes (denoted c‐FBP‐NC). The experimental characterizations and theoretical calculations show that the formed polarized P–N covalent bonds in c‐FBP‐NC can efficiently regulate electron transfer from NC to FBP and significantly promote the capture and catalysis of lithium polysulfides, thus alleviating the shuttle effect. Meanwhile, the robust 1D‐2D interwoven structure with large surface area and high porosity allows strong physical confinement and fast mass transfer. Impressively, with c‐FBP‐NC as the sulfur host, the battery shows a high areal capacity of 7.69 mAh cm−2 under high sulfur loading of 8.74 mg cm−2 and a low electrolyte/sulfur ratio of 5.7 μL mg−1. Moreover, the assembled pouch cell with sulfur loading of 4 mg cm−2 and an electrolyte/sulfur ratio of 3.5 μL mg−1 shows good rate capability and outstanding cyclability. This work proposes an interfacial and electronic structure engineering strategy for fast and durable sulfur electrochemistry, demonstrating great potential in lithium–sulfur batteries.

Preparation and optoelectronic properties of bulk black phosphorus crystals

In this paper, dense cylindrical shaped bulk black phosphorus (BBP)s are obtained by establishing a well-developed double growth zone technique through a chemical vapor phase transport (CVT) method. Extensive characterization tests confirm its high degree of orientation. XRD, SEM, TEM and Raman specturum are used to characterize the physical composition and structure of the prepared samples, confirming that the prepared BBP has good crystallinity and purity. Optical properties are evaluated, revealing distinct responses in UV–vis testing for black phosphorus (BP) of different sizes. Furthermore, the electrical properties of the bulk black phosphorus are measured, and it is found that the bulk black phosphorus is a P-type semiconductor. And the carrier mobility of the thin black phosphorus layer is 1233.81 cm2/V/S. The maximum Seebeck coefficient of 65.474 μV·K−1 along the growth direction of the column when the temperature difference is within 100 K.

Anisotropic thermo-mechanical response of layered hexagonal boron nitride and black phosphorus: application as a simultaneous pressure and temperature sensor.

Hexagonal boron nitride (hBN) and black phosphorus (bP) are crystalline materials that can be seen as ordered stackings of two-dimensional layers, which lead to outstanding anisotropic physical properties. Knowledge of the thermal equations of state of hBN and bP is of great interest in the field of 2D materials for a better understanding of their anisotropic thermo-mechanical properties and exfoliation mechanism towards the preparation of important single-layer materials like hexagonal boron nitride nanosheets and phosphorene. Despite several theoretical and experimental studies, important uncertainties remain in the determination of the thermoelastic parameters of hBN and bP. Here, we report accurate thermal expansion and compressibility measurements along the individual crystallographic axes, using in situ high-temperature and high-pressure high-resolution synchrotron X-ray diffraction. In particular, we have quantitatively determined the subtle variations of the in-plane and volumetric thermal expansion coefficients and compressibility parameters by subjecting these materials to hydrostatic conditions and by collecting a large number of data points in small pressure and temperature increments. In addition, based on the anisotropic behavior of bP, we propose the use of this material as a sensor for the simultaneous determination of pressure and temperature in the range of 0-5 GPa and 298-1700 K, respectively.

Atomically Doped 2D Black Phosphorus for Efficient and Stable Perovskite Solar Cells

Controlled functionalization of 2D black phosphorus (BP) nanosheets provides unique opportunities to tune their chemical, physical, and electronic properties. Herein, the preparation of single‐atom nickel‐doped BP (Ni–BP) sheets using a simple solution‐based strategy is reported. Using the Ni–BP sheets as a passivation layer on top of a perovskite film leads to standard perovskite solar cells (PSCs) with improved performance. The standard n–i–p PSCs with the Ni–BP interlayer achieve maximum power conversion efficiencies of over 22%, with negligible hysteresis and a modest improvement in stability when subjected to different testing conditions. The perovskite films prepared with Ni–BP sheets‐based passivation are found to have reduced defect densities as well as improved charge‐transfer properties and carrier lifetimes. Density‐functional theory calculations support the experimental results through showing that the atomic Ni‐doping increases the work function of the BP interlayer, enabling better hole extraction, as well as increasing the surface hydrophobicity of the BP layer, hence reducing water sorption into the perovskite film.

Near-Isotropic Local Attosecond Charge Transfer within the Anisotropic Puckered Layers of Black Phosphorus.

Black phosphorus possesses useful two-dimensional (2D) characteristics of van der Waals coupled materials but additionally features an in-plane anisotropic puckered layer structure that deviates from common 2D materials. Three distinct directions exist within the lattice of black phosphorus: the in-plane armchair and zigzag directions and the out-of-plane direction, with each distinct phosphorus 3p partial density of states. This structural anisotropy is imprinted onto various collective long-range properties, while the extent to which local electronic processes are governed by this directionality is unclear. At the P L1 edge, the directional selectivity of the core-hole clock method was used to probe the local charge transfer dynamics of electrons excited into the 3p-derived conduction band on an attosecond time scale. Here we show that the surprisingly small anisotropy of 3p electron transfer times reflects the similarly small differences in the 3p-derived unoccupied density of states caused by the underlying phosphorus bonding angles within the puckered layers.

High-pressure synthesis and low-temperature thermal expansion behavior of homogeneous phosphorus-rich pseudo-binary compound (V0.5Cr0.5)P4

A black phosphorus layered homogeneous phosphorus-rich compound – (V0.5Cr0.5)P4 is synthesized using a large volume press under conditions of P = 5 GPa, 1100 °C, and 1 h of heating. (V0.5Cr0.5)P4 has a monoclinic (C2/c) structure with lattice parameters and cell volume of a = 5.2307(3)Å, b = 10.861(4)Å, c = 5.8253(4)Å, β = 110.784°, and V = 309.41(4)Å3, respectively. The thermal expansion behavior above about 110K has been investigated by low-temperature synchrotron XRD. The coefficient of thermal expansion, α, was calculated to be αa = 0.57 × 10−5K−1, αb = 0.70 × 10−5K−1, αc = 0.92 × 10−5K−1, αβ = 0.13 × 10−5K−1 and αv = 2.10 × 10−5K−1 at 293K. This thermal expansion behavior presents an anisotropic expansion characteristic different from pure black phosphorus due to the V/Cr atom that bonded the black phosphorus layers together.

Layered Black Phosphorus Nanoflakes Reduce Bacterial Burden and Enhance Healing of Murine Infected Wounds

AbstractCurrent treatment modalities of cutaneous wound infections are largely ineffective, attributed to the increasing burden of antimicrobial resistance. S. aureus, a commonly wound‐associated pathogen continues to pose a clinical challenge, suggesting that new alternative therapeutic materials are urgently required to provide optimal treatment. A layered allotrope of phosphorus termed Black Phosphorus nanoflakes (BPNFs) has emerged as a potential alternative antibacterial material. However, wider deployment of this material requires extensive biological validation using the latest pre‐clinical models to understand its role in wound management. Here, the antibacterial potential of BPNFs against wound pathogens demonstrates over 99% killing efficiency at ambient conditions, while remaining non‐toxic to mammalian skin cells. In addition, in vivo validation of BPNFs using a preclinical model of S. aureus acute wound infection demonstrates that daily topical application significantly reduces infection (3‐log reduction) comparable to ciprofloxacin antibiotic control. Furthermore, the application of BPNFs also accelerates wound closure, increases wound re‐epithelization, and reduces tissue inflammation compared to controls, suggesting a potential role in alleviating the current challenges of infected cutaneous wounds. For the first time, this study demonstrates the potential role of BPNFs in ambient light conditions for clearing a clinically relevant wound infection with favorable wound healing properties.