Phosphorene Layers Research Articles

Casimir force tuning in 2D materials: effect of rotation in phosphorene

We theoretically examine the Casimir force with Lifshitz theory for two-dimensional media: graphene and phosphorene. We calculate the Casimir force for three different configurations: (a) phosphorene-graphene, (b) phosphorene-phosphorene (with rotation), and (c) a system composed of gold and a two-dimensional material (graphene or phosphorene). According to our calculations, we have determined that systems consisting solely of two-dimensional media can reduce the magnitude of the Casimir force by half or more, in comparison to systems composed of two-dimensional material and gold. The results show that in phosphorene configurations, high frequencies play a dominant role in contributing to the Casimir force, allowing greater force magnitudes for low interlayer distances compared to systems composed of gold or graphene. Our calculations also show that, as a result of the anisotropy of the phosphorene layers, it is possible to design a mechanical modulator with only two phosphorene layers by considering a relative rotation between them by an angle θ. In this regard, the anisotropy of phosphorene and the modulation of the separation between the phosphorene layers make it possible to tune the amplitude of Casimir force. The proposed configurations could lead to the development of nanotechnology applications incorporating 2D materials into their structures.

Revealing the potential of a C6BN/black phosphorene nanocomposite as an anode material for sodium-ion batteries by atomistic simulation: DFT and AIMD

Black phosphorus (BP) has recently been regarded as a promising anode for sodium-ion batteries (SIBs) owing to its high storage capacity, rapid Na mobility in its lamellar structure, and low redox potential. However, its poor cyclability due to structural instability hampers its further implementation in SIBs. Here, we propose to design a novel two-dimensional nanocomposite by vertically stacking a C6BN sheet on a black phosphorene layer (C6BN/Black-Pn). Atomistic simulations by the van der Waals corrected density functional theory method were conducted to assess the suitability of the designed C6BN/Black-Pn model as a potential anode in SIBs. Benefiting from C6BN's electronic and chemical features, Black-Pn's band gap in C6BN/Black-Pn is diminished to 0.14 eV, which disappears and indicates metallic character upon sodiation. Additionally, the optimized Na adsorption energy within the nanocomposite is decreased to −2.06 eV, compared to −1.76 eV in pure Black-Pn and −0.98 eV in C6BN, with a modest diffusion barrier of 0.23 eV. A maximal theoretical capacity of 568.77 mAh/g and a low potential of 0.48 V are predicted for the nanocomposite. The above evaluation of C6BN/Black-Pn electrode for SIBs may provide better insights into adopting a physical approach to address BP electrochemical failures for advanced energy storage.

The impacts of spin–orbit coupling and strain on transverse dynamical spin susceptibility in undoped phosphorene: Kane–Mele model study

We present the behaviors of dynamical transverse spin susceptibilities of undoped phosphorene monolayer using the Green’s function approach in the context of Kane–Mele model Hamiltonian. Such dynamical spin susceptibility is proportional to inelastic cross section of neutron beam from the layer. Specially, the effects of magnetic field and spin–orbit coupling strength on the spin excitation modes of phosphorene monolayer are investigated via calculating correlation function of spin density operators. Our results show the increase of magnetic field leads to move the magnetic excitation energy to higher values. Also, the intensity of peaks in inelastic cross section reduces with increase of magnetic field. We also show that applying both uniaxial and biaxial strains causes to decrease the intensity of peaks in dynamical spin susceptibility. Finally the effects of both compressive and tensile strains on frequency dependence of dynamical spin structure factor of phosphorene layer are studied. Moreover, the frequency positions of spin excitation mode of phosphorene layer have been investigated due to the effects of spin orbit coupling strength in details.

Surface plasmon resonance photonic crystal fiber biosensor: Utilizing silver-phosphorene nanoribbons for Near-IR detection

In recent years, the utilization of two-dimensional materials in photonic crystal fiber structures has developed the capabilities of biosensors in biological and biochemical applications. A photonic crystal fiber biosensor based on surface plasmon resonance with silver and phosphorene layers is proposed in this paper. Phosphorene helps with the prevention of oxidation of the silver layer used as a plasmonic active metal. The sensor performance can be optimized by changing the structural parameters. The maximum wavelength sensitivity obtained was 1800 nm/RIU in the dynamic index range of 1.39–1.45, and the proposed sensor also showed the maximum amplitude sensitivity of 268 RIU−1 with an analyte refractive index of 1.40. The performance of the proposed sensor was analyzed using the finite element method. The results show that using phosphorene may open a new window for the study of online biomolecular interaction.

Layer engineering in optoelectronic and photonic properties of single and few layer phosphorene using first-principles calculations.

Developing devices for optoelectronic and photonic applications-based nanomaterials has been one of the most critical challenges in the last decade. In this work, we use first-principles density functional theory combined with non-equilibrium Green's function to highlight for the first time the sensitivity of optoelectronic and photonic properties toward the exfoliation process. All the studied structures were relaxed and their relevant phonon modes confirm the high structural stability. The obtained phosphorene layers remained semiconducting with a direct band gap like the respective bulk structure with 10 layers. We also examined the effects of the thickness on the electron-hole interaction by calculating absorption energy combined with electron relaxation lifetimes. Additionally, we explore the optoelectronic properties, which can also be influenced by the exfoliation. Finally, we found that the current-voltage (I-V) characteristic shows higher sensitivity toward the bulk structure than the other 2D forms of phosphorene structures, meaning that the Schottky barrier at the interface of the bulk phosphorene is much lower than mono, and few layer phosphorene.

Berry curvature dipole and its strain engineering in layered phosphorene

The emergence of the fascinating non-linear Hall effect intrinsically depends on the non-zero value of the Berry curvature dipole. In this work, we predict that suitable strain engineering in layered van der Waals material phosphorene can give rise to a significantly large Berry curvature dipole. Using symmetry design principles, and a combination of feasible strain and staggered on-site potentials, we show how a substantial Berry curvature dipole may be engineered at the Fermi level. We discover that monolayer phosphorene exhibits the most intense Berry curvature dipole peak near 11.8% strain, which is also a critical point for the topological phase transition in pristine phosphorene. Furthermore, we have shown that the necessary strain value to achieve substantial Berry curvature dipole can be reduced by increasing the number of layers. We have revealed that strain in these van der Waals systems not only alters the magnitude of Berry curvature dipole to a significant value but allows control over its sign. We are hopeful that our predictions will pave way to realize the non-linear Hall effect in such elemental van der Waals systems.

An efficient biosensor based on plasmon-induced transparency effect in plasmonic-graphene-black phosphorous absorber for diabetes diagnosis

In this work, an efficient absorber (biosensor) based on the combinations of graphene – plasmonic - black phosphorous configurations is proposed and investigated. The presented absorber is considered to operate based on the plasmon-induced transparency (PIT) effect. The presented absorber is based on various layers of graphene, phosphorene and gold in the ring and plate shapes. In the bio-sensing application, the analyte would be inserted in the upper layer while being in contact with the incident light wave. By considering the PIT effect, the absorber would be further improved (improving the absorption's peak value). In order to fulfill the improvement, effects of structural parameters (R1, R2, R3, R4, h1, h2, h3) and chemical potential(Ef) would be investigated. After the improvement process, the structure would be utilized as a biosensor for detection the Glucose concentrations in blood samples. By detecting Glucose concentrations in blood samples, physicians can diagnose diabetes in early stages. Finally, the sensitivity factor, figure of merit (FOM), full width at half maximum (FWHM) and Q-Factor of 2686.5 nm/RIU, 134.325 RIU−1, 20 nm and (58.5–76.5) would be achieved, respectively. As a result, the proposed absorber (biosensor) can be a remarkable and great candidate for bio-sensing applications in optical integrated circuits.

Tuning Gaps and Schottky Contacts of Graphene/Phosphorene Heterostructures by Vertical Electric Field and Strain.

We present a comprehensive study of the structural and electronic properties of a graphene/phosphorene (G/P) heterostructure in the framework of density functional theory, including van der Waals interaction in the exchange-correlation functional. While the G(4 × 1)/P(3 × 1) superlattice usually used in the literature is subject to a strain as high as about 7%, the in-plane strain could be drastically reduced to under 1% in the G(4 × 13)/P(3 × 12) heterostructure investigated here. Adapting the lattice constants of the rectangular lattices, the equilibrium configuration in the xy plane of phosphorene relative to the graphene layer is optimized. This results in an equilibrium interlayer distance of 3.5 Å and a binding energy per carbon atom of 37 meV, confirming the presence of weak van der Waals interaction between the graphene and the phosphorene layers. The electronic properties of the heterostructure are evaluated under different values of interlayer distance, strain and applied vertical electric field. We demonstrate that G/P heterostructures form an n-type Schottky contact, which can be transformed into p-type under external perturbations. These findings, together with the possibility to control the gaps and barrier heights, suggest that G/P heterostructures are promising for novel applications in electronics and may open a new avenue for the realization of innovative optoelectronic devices.

Interaction of Water and Oxygen Molecules with Phosphorene: An Ab Initio Study.

Phosphorene, the 2D form of black phosphorus, has recently attracted interest for optoelectronic and tribological applications. However, its promising properties are affected by the strong tendency of the layers to oxidize in ambient conditions. A significant effort has been made to identify the role of oxygen and water in the oxidation process. In this work, we introduce a first-principles study of the phosphorene phase diagram and provide a quantitative estimate of the interaction of pristine and fully oxidized phosphorene layers with oxygen and water molecules. Specifically, we study oxidized layers with oxygen coverages of 25% and 50% that keep the typical anisotropic structure of the layers. We found that hydroxilated and hydrogenated phosphorene layers are both energetically unfavorable, leading to structural distortions. We also studied the water physisorption on both pristine and oxidized layers, finding that the adsorption energy gain doubled on the oxidized layers, whereas dissociative chemisorption was always energetically unfavorable. At the same time, further oxidation (i.e., the dissociative chemisorption of O2) was always favorable, even on oxidized layers. Ab initio molecular dynamics simulations of water intercalated between sliding phosphorene layers showed that even under harsh tribological conditions water dissociation was not activated, thus further strengthening the results obtained from our static calculations. Overall, our results provide a quantitative description of the interaction of phosphorene with chemical species that are commonly found in ambient conditions at different concentrations. The phase diagram that we introduced confirms the tendency of phosphorene layers to fully oxidize due to the presence of O2, resulting in a material with improved hydrophilicity, a piece of information that is relevant for the application of phosphorene, e.g., as a solid lubricant. At the same time, the structural deformations found for the H- and OH- terminated layers undermine their electrical, mechanical, and tribological anisotropic properties and, therefore, the usage of phosphorene.

Effects of hexagonal boron nitride encapsulation on the electronic properties of Cu, Li, and O-doped black phosphorus monolayer

In this work, the structural and electronic properties of Cu, Li, and O-doped phosphorene/hexagonal boron nitride systems were studied based on density functional theory calculations. The intrinsic physical properties of the pristine phosphorene layer do not change with the addition of hexagonal boron nitride layers. While doping of phosphorene leads to strong binding energy at the interface, hence, improving the stability of the doped phosphorene/hexagonal boron nitride layers in systems. The electronic properties of the encapsulated systems change after doping. The band gap also decreases from 1.1200 eV in pristine encapsulated phosphorene to 0.3087, 0.0076, and 0.3100 eV in encapsulated phosphorene doped with Li, Cu, and O, respectively. The partial density of states and band structure diagrams show that the electronic properties of these systems shift from semiconductor to metallic behavior which can be exploited in electronic and optical applications.

Dirac Fermions in Blue Phosphorene Monolayer

Abstract2D materials beyond graphene and in particular 2D semiconductors have raised interest due to their unprecedented electronic properties, such as high carrier mobility or tunable bandgap. Blue phosphorene is an allotrope of black phosphorene that resembles graphene as it presents a honeycomb structure. However, it is known to have semiconductor character and the crucial point is to determine whether this hexagonal phase of phosphorene presents Dirac fermions as in graphene. Here, the first compelling experimental evidence of Dirac fermions in blue phosphorene layer grown on Cu(111) surface is presented. The results highlight the formation of a highly ordered blue phosphorene sheet with a clear Dirac cone at the high symmetry points of the Brillouin Zone. The charge carriers behave as massless relativistic particles. Therefore, all the expectations held for graphene, such as high‐speed electronic devices based on ballistic transport at room temperature, may also be applied to blue phosphorene.

Designing a perfect Phosphorene-Plasmon absorber and investigating its geometric irregularity effects: A simulation study

Optical absorbers have many applications in the field of optoelectronics, photovoltaics, and energy harvesting because of their capability to absorb electromagnetic waves, as well as their ability to adjust the absorption of specific wavelengths in the mid-IR region. In this study, a perfect optical absorber was designed, which included a gold reflective substrate, Al2O3 grating, a phosphorene layer, and air. By using the finite element method, the effects of irregularities on the geometry of the grating were investigated. Results show that, in the designed structure, irregular grating did not cause a significant change in the amount of absorption, and the absorption value for the phosphor layer remained at 99.9%. This perfect absorber also showed a stable wide range of absorption of up to 7.5 µm. Changing the incident light angle in the range of 0 to 50 degrees reduced the absorption in the phosphor layer by less than 10%.

Hexagonal Boron Nitride Nanosheets Protect Exfoliated Black Phosphorus Layers from Ambient Oxidation

AbstractBlack phosphorus‐based 2D materials have yet to demonstrate their full application potential because of the well‐known sensitivity of phosphorene to spontaneous oxidation under ambient conditions. It is hypothesized that this unfavorable process can be prevented by drop‐casting hexagonal boron nitride (h‐BN) nanosheets on phosphorene. Here, both materials are prepared by sonication‐assisted liquid‐phase exfoliation of bulk materials and characterized by transmission electron microscopy and Raman spectroscopy. Raman spectroscopy is also utilized for the real‐time monitoring of phosphorene oxidation by calculating the A1g/A2g intensity ratio. This value drops below 0.5 (corresponding to complete oxidation) within 100 min for pristine phosphorene layers in the air. However, it remains constant above 0.6 (indicating no oxidation) when phosphorene covered by h‐BN sheets is left in the air. Moreover, deploying h‐BN sheets at midterm during the ambient oxidation reaction is able to halt the process and maintain a steady 0.5 < A1g/A2g < 0.6 Raman intensity ratio. The experimental results are successfully interpreted within the developed theoretical framework by the charge distribution of h‐BN, which keeps O2 molecules from interacting with its surface, and the fact that the first O2 molecules in contact react with the edges of h‐BN, thus creating a barrier for subsequently arriving O2 molecules.

Effects of Mechanical Strain on Electronic Properties of Phosphorene Structure in the Presence of Spin-Orbit Coupling

In this paper, we present a Kane-Mele model in the presence of magnetic field and next nearest neighbors hopping amplitudes for investigations of the electronic and transport properties of monolayer phosphorene. We have also considered the effects of uniaxial and biaxial in-plane strain on the electronic behavior of phosphorene layer. Moreover the impact of out-of-plane strain on density of states of phosphorene layer has been studied. Specially, the temperature dependence of static thermal conductivity of phosphorene layer has been studied due to magnetic field, spin-orbit coupling and strain effects. The Kane Mele model Hamiltonian has been applied for describing the electron dynamics. We have exploited the linear response theory and Green’s function approach to obtain the temperature behavior of thermal conductivity, electrical conductivity, Seebeck coefficient and figure of merit. Our numerical results indicate, thermal conductivity increases upon increasing the temperature in the low amounts region. This fact comes from the increasing of thermal energy of charge carriers and excitation of them to the conduction bands. The temperature dependence of seebeck coefficient show the thermopower gets negative sign at high temperatures in the presence of spin-orbit coupling and strain effects. The effects of both spin orbit coupling, magnetic field factors on temperature behavior of electrical conductivity of phosphorene monolayer have been investigated in details. Moreover the effects of both in-plane uniaxial and biaxial strains on transport properties of single layer phosphorene have been addressed.

Thermal boundary conductance of monolayer beyond-graphene two-dimensional materials on SiO2 and GaN

Two-dimensional (2D) materials have emerged as a platform for a broad array of future nanoelectronic devices. Here we use first-principles calculations and phonon interface transport modeling to calculate the temperature-dependent thermal boundary conductance (TBC) in single layers of beyond-graphene 2D materials silicene, hBN, boron arsenide (BAs), and blue and black phosphorene (BP) on amorphous SiO2 and crystalline GaN substrates. Our results show that for 2D/3D systems, the room temperature TBC can span a wide range from 7 to 70 MW m−2 K−1 with the lowest being for BP and highest for hBN. We also show that 2D/3D TBC has a strong temperature dependence that can be alleviated by encapsulating the 2D/3D stack. Upon encapsulation with AlO x , the TBC of several beyond-graphene 2D materials can match or exceed reported values for graphene and numerous transition-metal dichalcogendies which are in the range of 15–40 MW m−2 K−1. We also compute the room temperature TBC as a function of van der Waals spring coupling (K a ) where the TBC falls in the range of 50–150 MW m−2 K−1 at coupling strengths of K a = 2–4 N m−1 for silicene, BAs, and blue phosphorene. We further identify group III–V materials with ultra-soft flexural branches as being promising 2D materials for thermal isolation and energy scavenging applications when matched with crystalline substrates.

Effective plasma frequency in tunable THz reflectors based on graphene and phosphorene

In this work, we show that a THz reflector made of a phosphorene (graphene)–dielectric multilayer can be analyzed through a simple effective plasma frequency model. We obtain the cutoff frequency, marking the beginning of the transmission region in terms of the effective plasma frequency, which depends on structural parameters of the multilayer and, more importantly, on the carrier density of phosphorene (graphene) layers. This implies that the cutoff frequency can be varied when considering carrier density tuning. We also show that the frequency regime, where cutoff frequency is obtained by carrier density tuning, goes through a wide range in the THz domain (3–25 THz), making the design of tunable reflectors in these frequencies possible through electrical doping. We numerically analyze the cutoff frequency as a function of carrier density and optical thickness of the multilayer, finding that the cutoff frequency and carrier density of phosphorene (graphene) have a very simple quadratic (quartic) relation. Our analysis allows us to obtain ranges where the effective analytical model fits better with the cutoff frequency computed from photonic bands for the multilayer periodic structure.

Unusual anisotropic behavior of free-carrier-induced third-harmonic generation in phosphorene at microwave frequencies

We theoretically investigate the microwave third-harmonic generation (THG) produced by free carriers in the conduction band of electrostatically doped phosphorene. It is assumed that a plane polarized microwave of frequency ω is incident normally on the phosphorene layer deposited on a dielectric substrate. Using an extremely simple model for the phosphorene’s anisotropic electronic structure, we calculate the power P(3ω) of the third harmonic wave generated in the reflected direction for the two principal cases of polarization of the incident radiation either along the ‘armchair’ () direction or along the ‘zigzag’ () one. Our results for and reveal an unusual anisotropy in the output THG power: the ratio varies from values less than 1 to values greater than 1 with an increase in the frequency ω at a fixed value of the electron density n S controlled by an external gate voltage. The effect predicted may be useful in providing a THG functionality in microwave devices, such as frequency multipliers and up-convertors, needed for developing high data rate communication links.

Magnetic anisotropy in Co/phosphorene heterostructure

Magnetic anisotropy (MA) in magnetic multilayer structures plays a critical role in the design of future spintronic and magnetic devices. This property is more important for structures with a thickness of few angstroms, such as few-layer two-dimensional materials. Here, we determined the variation in the interface MA in mono- and bi-layer Co/phosphorene heterostructures via first-principles density functional theory calculations. We found that the MA of these structures was comparable to those of ferromagnet/heavy-metal interfaces, despite the small spin-orbit coupling strength of phosphorus atoms. The hybridization of the metal d and the phosphorene p orbitals is well manifested in the projected density of states of these systems. The strain dependence of the magnetic anisotropy energy (MAE) in bilayer Co/phosphorene heterostructures under uniaxial strains along zigzag and armchair directions of the phosphorene layer was investigated, indicating that the MAE of the system increases by more than 80% by applying the strain. More specifically, by utilizing the uniaxial tensile strain along the zigzag direction of this structure, we found that MA could vary from perpendicular to in-plane directions. Our findings indicate that interlayer hybrid bonds in two-dimensional layered materials can be a promising approach to tailoring the MA property.

Li interaction-induced phase transition from black to blue phosphorene

A comprehensive first-principles calculation has been carried out revealing that at sufficiently high Li concentration and certain well-defined configurations a phase transition from black to blue phosphorene can take place. Blue phosphorene, a newly predicted allotrope of phosphorus, possesses unique crystalline and electronic structure and is a promising candidate, not only for fundamental research but also for electronic and optoelectronic applications. Methods of growing high-quality blue phosphorene layers are highly desirable but challenging. Here, a kinetic pathway to grow blue phosphorene layers from black phosphorene layers via Li intercalation is proposed based on first-principles study. This study pointed out that Li atoms intercalated in black phosphorene could act as a ``catalyst'' in the ``reactive region'' of the lone pair of P atoms, leading to a P-P bond breaking and, subsequently, a local structural transformation from an orthorhombic lattice to an assembly of parallel narrow nanoribbons with rhombohedra-like symmetry. During Li deintercalation, these nanoribbons are self-mended and form blue phosphorene layers. The interlayer distance was found to be 4.60 \AA{} for a double layer with AA stacking and 4.13 \AA{} for a multilayer with ABC stacking, indicating monolayer blue phosphorene can be mechanically exfoliated. This study also points out the possibility of new phases in other systems, where intercalation can lead to an unexpected structural phase transition and even a discovery of novel materials.

Hexagonal borophene sandwiched between blue phosphorenes: A novel bonding heterostructure as an anchoring material for lithium-sulfur batteries

A novel 2D bonding heterostructure consisting of hexagonal borophene monolayer bonding with two blue phosphorene layers was designed theoretically, which possesses high stability, good conductivity and high in-plane stiffness. Subsequently, the heterostructure as an anchor material for lithium-sulfur (Li-S) batteries was investigated systematically by using density functional theory. Our results indicate that lithium polysulfides on the heterostructure have appropriate adsorption energies (0.60–2.68 eV) and moderate diffusion barriers (0.09–0.31 eV), which can suppress the “shuttle effect” and inhibit the agglomeration of lithium polysulfides. Therefore, the novel heterostructure can hold great promise as an anchoring material for Li-S batteries.