Structure Of Phosphorene Research Articles

Strain-engineered p-type to n-type transition in mono-, bi-, and tri-layer black phosphorene

Using density functional theory, a detailed computational study is performed to explore the structural and electronic properties of a black phosphorene monolayer, bilayer, and trilayer under a uniaxial strain along the armchair (b axis) and zigzag (a axis) directions. In the case of a monolayer black phosphorene, it is found that strain along the armchair direction slightly affects the a lattice parameter and the puckering height (Δ). Along the zigzag direction, however, variation of the a lattice parameter is compensated by both the a and b lattice variations while the parameter Δ remains unaffected. In the case of bilayer and trilayer black phosphorene, a similar behavior is observed where the layer-spacing “d” acts as an additional degree of liberty for strain compensation. In terms of electronic properties, strain along the armchair and zigzag directions changes the nature of the Γ point in the bandgap from a direct to an indirect electronic transition as a function of the strain value. In the strain range from −14% to +6%, all black phosphorene structures behave similarly to classical semiconductors. However, the size and strain combined effect significantly affects the Fermi energy position. Around 0% strain, all black phosphorene structures are of p-type, while they switch to an n-type semiconductor in the range of strain values from +2% up to +14%. This p-type to n-type transition may have a major technological impact in fields where mono- and hetero-junctions are considered.

Theoretical Study of Electronic Properties of Nanostructures Composed of Blue Phosphorene and Graphene Sheet

In this study, structural and electronic properties of the single-layer structure of Graphene, the single-layer structure of blue Phosphorene, the two-layer structure of blue Phosphorene/Graphene, the three-layer structure of blue-Phosphorene/Graphene/blue-Phosphorene and the three-layer structure of Graphene/blue-Phosphorene/Graphene have been investigated. The calculations are conducted based on the density functional theory (DFT) and using SIESTA code and generalized gradient approximation (GGA). The results show that the single-layer structure of Graphene reveals quasi-metallic behavior, and the single-layer structure of blue Phosphorene exhibit semiconducting behavior. Two - and three-layer structures of Graphene and blue Phosphorene have a metallic behavior. Total energy and structural stability have also been investigated.

Charge transport in nnn and npn phosphorene junctions: The use of phosphorene pn junctions as rectifiers

Abstract We investigate quantum charge transport of nnn and npn junctions based on two-dimensional black phosphorus (BP), phosphorene. We observe an oscillatory behavior for both the transmission probability and tunneling conductance of phosphorene nnn and npn junctions as a function of the chemical potential and width of the middle tunnel barrier. The oscillating amplitudes and periods can be controlled by means of a top gate voltage in the second segment. Because of the anisotropy of the electronic structure of phosphorene, the transmission probability depends strongly on the direction of the incident electron beam. We show that the perfect transmission can be selected by tuning the chemical potential and width of the middle region as well as the incidence angle of the carriers. In particular, for the n n n regime for the lightly doped case of the middle region, the transmission for any width of the middle region nearly becomes perfect. Under the certain conditions an electron is not allowed to tunnel through the junction that could be used as a single electron transistor. The resulting electronic properties show that the planar pn junctions (PNJs) structures based on phosphorene could be used as rectifiers, showing excellent tunability and novel functionalities. Our findings will open a new way to nanoelectronics based on field-effect tunneling transistors as well as the single electron transistors based on phosphorene heterostructures.

High-performance phosphorene electromechanical actuators

Phosphorene, a two-dimensional material that can be exfoliated from black phosphorus, exhibits remarkable mechanical, thermal, electronic, and optical properties. In this work, we demonstrate that the unique structure of pristine phosphorene endows this material with exceptional quantum-mechanical performance by using first-principles calculations. Upon charge injection, the maximum actuation stress is 7.0 GPa, corresponding to the maximum actuation strain as high as 36.6% that is over seven times larger than that of graphene (4.7%) and comparable with natural muscle (20–40%). Meanwhile, the maximum volumetric work density of phosphorene (207.7 J/cm3) is about three orders of magnitude larger than natural muscle (0.008–0.04 J/cm3) and approximately six times larger than graphene (35.3 J/cm3). The underlying mechanism of this exceptional electromechanical performance in phosphorene is well revealed from the analysis of atomic structure and electronic structure. Finally, the influence of charge on the mechanical behaviors of phosphorene is examined by mechanical tests, indicating the sufficient structural integrity of phosphorene under the combined electromechanical loading. These findings shed light on phosphorene for promising applications in developing nanoelectromechanical actuators.

Sensitivity enhancement of an SPR biosensor with a graphene and blue phosphorene/transition metal dichalcogenides hybrid nanostructure.

A novel surface plasmon resonance (SPR) biosensor based on Ag-Au bimetallic films with a hybrid structure of blue phosphorene (BlueP)/transition metal dichalcogenides (TMDCs) and graphene is presented. In order to improve the sensitivity, the thickness of silver and gold films is optimized to achieve minimum reflectivity and an adequate level of sensitivity; further, sensitivity for the monolayer BlueP/MoS2 and graphene structure is enhanced by 19.73%, with respect to a traditional sensor. Besides, the effect of layers of different Blue/TMDCs heterostructures to the sensitivity of the SPR biosensor is investigated, and the highest sensitivity with 335.4°/RIU for the bilayer BlueP/WS2 is obtained. Furthermore, distributions of the electric field and the changes of resonance angle to the refractive index of the sensing medium and prism in the visible regime are illustrated at optimal configuration. In virtue of highly sensitive characteristics, the proposed sensor structure will be a much better option to be employed for further biological detection.

Adsorption of rare gases on pristine and doped phosphorene

Phosphorene has broad application prospects for adsorption due to the unique combination of ultrahigh surface-volume ratio and high chemical reactivity. The adsorption behavior of rare gases (He, Ne, Ar, Kr and Xe) on pristine and doped phosphorene systems were studied with first-principle calculation. The adsorption energies of rare gases on pristine phosphorene are comparable to graphene. The electronic structure of phosphorene can be widely tuned by doping heteroatoms. The adsorption abilities of rare gas on doped phosphorene are significantly enhanced, in particular for Li-doped phosphorene. The phosphorene with surface decorated is a promising material for capture of noble gases, especially for the radioactive Kr and Xe.

Binary Phosphorene Redox Behavior in Oxidoreductase Enzymatic Systems.

Phosphorene is a two-dimensional material that has many advantageous electronic, electrochemical, and optical properties. However, phosphorene possesses a relatively poor stability in ambient atmosphere. This disadvantage limits its application in several systems and particularly in electrochemical biosensors. Here we evaluate phosphorene as an electrochemical biosensing platform in two different mediator-based oxidoreductase enzymatic systems (glucose oxidase (GOx) and peroxidase from horseradish (HRP)), in which their detection is based on the reduction or oxidation of a mediator. In both cases, the used mediator is the same, ferrocene methanol (FcMeOH). Enhanced electrochemical activity is observed only in the reductive system (HRP-based biosensor) when compared to the oxidative counterpart (GOx-based biosensor). This phenomenon is attributed to the fact that in a reductive environment the phosphorene structure remains intact, while in an oxidative potential, the phosphorene is readily oxidized. In this way, the electroactivity of phosphorene as a sensing platform is strongly dependent on the type of mediator-based enzymatic system. These findings of binary nature of phosphorene are of high importance for construction of phosphorene-sensing platforms and in the development of enzyme logic systems.

Modulation of Phosphorene for Optimal Hydrogen Evolution Reaction.

Economical and highly effective catalysts are crucial to the electrocatalytic hydrogen evolution reaction (HER), and few-layer black phosphorus (phosphorene) is a promising candidate because of the high carrier mobility, large specific surface area, and tunable physicochemical characteristics. However, the HER activity of phosphorene is limited by the weak hydrogen adsorption ability on the basal plane. In this work, optimal active sites are created to modulate the electronic structure of phosphorene to improve the HER activity and the effectiveness is investigated theoretically by density-functional theory calculation and verified experimentally. The edges and defects affect the electronic density of states, and a linear relationship between the HER activity and lowest unoccupied states (εLUS) is discovered. The medium εLUS value corresponds to the suitable hydrogen adsorption strength. Experiments are designed and performed to verify the prediction, and our results show that a smaller phosphorene moiety with more edges and defects exhibits better HER activity and surface doping with metal adatoms improves the catalytic performance. The results suggest that modified phosphorene has large potential in efficient HER and provides a convenient standard to explore ideal electrocatalysts.

Optoelectronic properties of phosphorene quantum dots functionalized with free base porphyrins

Electronic and optical properties of phosphorene quantum dots functionalized with an organic molecule, porphyrin, are investigated using density functional theory with two different van der Waals functionals. The electronic structure of this complex is obtained and with this information, the real and imaginary parts of the dielectric function are calculated, from which, the interband optical response can be determined. Depending on the size of the quantum dot and the relative orientation between the dot and the organic molecule, it is found that the porphyrin physisorption leads to important modifications of the energy spectrum of the functionalized blue phosphorene quantum dots. These changes reflect in the optical response of the complex which shows features that come from both the blue phosphorene structure and the organic molecule. It is also found that the rotations of the molecule with respect to the phosphorene quantum dot do not practically alter the value of the binding energy.

K·p theory for phosphorene: Effective g -factors, Landau levels, and excitons

Phosphorene, a single layer of black phosphorus, is a direct-band gap two-dimensional semiconductor with promising charge and spin transport properties. The electronic band structure of phosphorene is strongly affected by the structural anisotropy of the underlying crystal lattice. We describe the relevant conduction and valence bands close to the $\Gamma$ point by four- and six-band (with spin) $k \cdot p$ models, including the previously overlooked interband spin-orbit coupling which is essential for studying anisotropic crystals. All the $k \cdot p$ parameters are obtained by a robust fit to {\it ab initio} data, by taking into account the nominal band structure and the $k$-dependence of the effective mass close to $\Gamma$-point. The inclusion of interband spin-orbit coupling allows us to determine dipole transitions along both armchair and zigzag directions. The interband coupling is also key to determine the effective g-factors and Zeeman splittings of the Landau levels. We predict the electron and hole g-factor correction of $\approx 0.03$ due to the intrinsic contributions in phosphorene, which lies within the existing range of experimental data. Furthermore, we investigate excitonic effects using the $k \cdot p$ models and find exciton binding energy (0.81 eV) and exciton diameters consistent with experiments and {\it ab initio} based calculations. The proposed $k \cdot p$ Hamiltonians should be useful for investigating magnetic, spin, transport, optical properties and many-body effects in phosphorene.

Phonon limited anisotropic quantum transport in phosphorene field effect transistors

Electron-phonon coupling limited transport in phosphorene metal oxide semiconductor field effect transistors (MOSFETs) is studied along the armchair (AC) and zigzag (ZZ) directions. In a multiscale approach, the unit cell of phosphorene is first relaxed, and the band structure is calculated using hybrid density functional theory (DFT). The transport equations are then solved quantum mechanically under the nonequilibrium Green’s function formalism using DFT-calibrated two-band k⋅p hamiltonian. The treatment of electron-phonon scattering is done under the self-consistent Born approximation in conjunction with deformation potential theory. It is found that optical phonon modes are largely responsible for degradation of ON-current apart from p-channel AC MOSFET where acoustic phonon modes play a stronger role. It is further observed that electron-phonon scattering is more pronounced in the ZZ direction, whereas the diffusive ON-current of p-MOSFET in a given direction is higher than n-MOSFET. Further study on the complex band structure of phosphorene reveals band wrapping within the bandgap region in the AC direction and multiple crossings in the ZZ direction. This signifies strong phonon-assisted tunneling in the ZZ direction in comparison with the AC direction. For completeness, drain current in the AC tunnel field effect transistor is calculated, and electron-phonon scattering is observed only in the near vicinity of the OFF-current.

Effect of stacking structure on lithium adsorption and diffusion in bilayer black phosphorene

Intercalation of lithium in few-layer phosphorene has aroused great concern because of the prospects of few-layer phosphorene as an anode material for high-performance lithium-ion batteries (LIBs). In this paper, we adopt first-principles calculations to explore in detail the effects of stacking structure of bilayer black phosphorene (BBP) on the adsorption and diffusion of lithium in BBP. Our calculated results indicate that Li energetically prefers to intercalate within rather than adsorb outside BBP, and it exists in a cationic state. Moreover, the stacking structure of BBP has very important effects on Li adsorption, the open-circuit voltage, and Li diffusion in BBP. Additionally, Li diffusion in BBP exhibits directional preference, with diffusing along the zigzag direction being easier. The analyses of the potential distribution indicate that the puckered honeycomb structure of monolayer phosphorene and the stacking structure of BBP greatly cause low-potential channels along the zigzag direction, which directly lead to the directional preference in Li diffusion. More interestingly, our results suggest that BBP with AC stacking is the most beneficial for Li adsorption and diffusion. These findings suggest that changing the stacking structure of BBP is one possible way to rationally design the anode material in high charge/discharge rate LIBs based on BBP.

Triaxial strain engineering of magnetic phase in phosphorene

In the present paper, we theoretically address and predict the magnetic properties of monolayer phosphorene under different triaxial strains. For this purpose, we use the tight-binding Hamiltonian model and the Harrison rule aiming at studying the strain-induced phosphorene structure. Our findings indicate how the electronic phase transition is related to the magnetic phase transition in phosphorene. The details of this connection are extracted from the bandgap-dependent Neel temperature of the antiferromagnetic ground state phase as well as the state degeneracy-dependent Pauli spin paramagnetic susceptibility. We found that phosphorene keeps its semiconductor nature for the uniform and nonuniform triaxial strains (both compressive and tensile strains), resulting in no magnetic phase transition, whereas the in-plane uniform triaxial strains lead to a semiconductor-to-semimetal and consequently an antiferromagnetic-to-ferromagnetic phase transition on average. Furthermore, we show that the armchair edge possesses the most contribution to the electronic and magnetic phases of monolayer phosphorene. These results provide useful information for future experimental research studies in both optoelectronic and spintronic applications.

Exploring the electronic, charge transport and lattice dynamic properties of two-dimensional phosphorene

Two-dimensional nanostructures are emerging materials for device applications. Development of the field require materials with high carrier mobility and sufficient band gap. Two-dimensional black phosphorus (phosphorene) is a novel material with potential applications in nanoelectronics. Herein, employing density functional theory, the electronic structure, carrier mobility, structural stability, and Raman active modes of phosphorene are studied. Using PBE functional, it is found that phosphorene shows a direct band gap 0.95 eV. From deformation potential theory, the mobility of phosphorene is found to be of the order of 103 cm2 V−1 s−1, and is found to be nearly same for electrons along x- and y-direction (μx ~ μy), whereas, it is significantly larger for holes (μy = 105.36μx) along y-direction. Also, no softmodes ware seen in phonon dispersion which indicates that phosphorene is dynamically stable material. The vibrational modes at Γ-point shows that all even parity modes are Raman active.

Superior Photo-thermionic electron Emission from Illuminated Phosphorene Surface

This work demonstrates that black phosphorene, a two dimensional allotrope of phosphorus, has the potential to be an efficient photo-thermionic emitter. To investigate and understand the novel aspects we use a combined approach in which ab initio quantum simulation tools are utilized along with semiclassical description for the emission process. First by using density functional theory based formalism, we study the band structure of phosphorene. From the locations of electronic bands, and band edges, we estimate the Fermi level and work function. This leads us to define a valid material specific parameter space and establish a formalism for estimating thermionic electron emission current from phosphorene. Finally we demonstrate how the emission current can be enhanced substantially under the effect of photon irradiation. We observe that photoemission flux to strongly dominate over its coexisting counterpart thermionic emission flux. Anisotropy in phosphorene structure plays important role in enhancing the flux. The approach which is valid over a much wider range of parameters is successfully tested against recently performed experiments in a different context. The results open up a new possibility for application of phosphorene based thermionic and photo-thermionic energy converters.

Electronic and magnetic properties of doped black phosphorene with concentration dependence.

In this paper, we employed first-principles calculations and chose Si and S atoms as impurities to explore the concentration-dependence of electronic structure and magnetism of doped phosphorene. It is found that the stability of doped phosphorene improves continuously with increasing the supercell size and decreasing impurity concentration due to the reduction of deformation. The stability of pristine phosphorene is invariable. The band structures of Si- and S-doped phosphorene without spin polarization always show metallic states suggesting the bandgap is insensitive to the in-plane size of the supercell and the dopant content. However, the results are fairly different once the spin polarization is taken into account. The band structures of Si- and S-doped phosphorene become those of a semimetal or a semiconductor as the in-plane size of the supercell goes up to 4 × 4 × 1 or 5 × 5 × 1 and the concentration goes down to 1.56% or 1%, respectively. In addition, we also observe that all Si- and S-doped phosphorene are magnetic, except for the Si-doped phosphorene with 2 × 2 × 1 supercell and a dopant content of 6.25%. The magnetic moment induced by 3p orbit–spin splitting increases with the in-plane size of the supercell, and the largest magnetic moment can be found in 4 × 4 × 1 and 5 × 5 × 1 supercells. These findings offer an alternative method to tune the magnetism and electronic structure of black phosphorene, which might be beneficial for its application in future spintronic devices.

SnSe monolayer: A promising candidate of SO2 sensor with high adsorption quantity

Recently, the application of phosphorene structure analogues in gas sensors has been a hot research topic since the appearance of phosphorene. SnSe monolayer as one of them has been proved to be much more stable properties than phosphorene. Based on the density-functional theory, the interaction between gas molecules (CO, CO2, O2, NO, NH3, SO2 and NO2) and SnSe monolayer are theoretically investigated by first-principles calculation. Macroscopically, gas molecules selective adsorption of SnSe monolayer is analyzed by molecular dynamics. Compared to CO, CO2, O2, SnSe monolayer performs stronger affinity for SO2 and NO2, which possesses appropriate adsorption energies (−6.000 eV and −0.759 eV) and elevated charge transfers (−0.239 e and −0.328 e). SnSe monolayer chemical adsorption of NO2, while physically adsorbing SO2, is more suitable for the adsorption mode of SO2 sensors. Surprisingly, the adsorption amount of SO2 is 6 times that of NO2. Therefore, the adsorption of SO2 is more likely to occur compared to other gas molecules. For a mixed environment of SO2 and NO2, the adsorption quantity of SO2 is not significantly affected, while the adsorption of NO2 is inhibited. Therefore, the SnSe monolayer could be a promising candidate as SO2 sensors with high selectivity and sensitivity.

Strain-induced electronic phase transition in phosphorene: A Green’s function study

In the present paper, we study the impacts of possible uni-, bi-, and tri-axial strains on the electronic band gap of phosphorene using the density of states (DOS) quantity through the Harrison relation. To reach this goal, we use a tight-binding Hamiltonian model and the Green’s function method. The findings report that the electronic phase of phosphorene can be adjustable in the presence of strain. The band gap increases (decreases) when applying the tensile uniaxial strains along the {x,y} (z) direction, while it decreases (increases) when the compressive uniaxial ones are applied. Interestingly, due to the inherent highly anisotropic structure of phosphorene, there is a semiconductor-to-metal phase transition along the z direction as the tensile strain is increased. Furthermore, we found that among all possible configurations for uniform biaxial strains, a flat band emerges at εx=εy=-15%, which is a quite new outcome. In addition, phosphorene supports different phase transitions when the triaxial strains are applied, introducing new electro-optical features. Hence, these findings can provide insights into the future experimental research and improve the applications of phosphorene in the real industry such as field-effect transistors.

The thermodynamic critical field and specific heat of superconducting state in phosphorene under strain

In this work, we present the thermodynamic properties of the superconducting state in phosphorene. In particular, we have examined the electron doped [Formula: see text] and biaxially strained (4%) monolayer of black phosphorous, which exhibits best thermodynamic stability and highest superconducting critical temperature [Formula: see text] among all monolayer phosphorene structures. Due to the confirmed electron–phonon pairing mechanism and relatively high electron–phonon coupling constant in the studied material, we carried out the calculations in the framework of the Eliashberg formalism for a wide range of the Coulomb pseudopotential [Formula: see text]. We have determined the thermodynamic critical field [Formula: see text], and the specific heat difference [Formula: see text] between superconducting [Formula: see text] and normal state [Formula: see text] as the functions of the temperature. In addition, we have calculated the dimensionless parameters [Formula: see text]/[Formula: see text] and [Formula: see text]/[Formula: see text], and also found their significant deviation from the expectations of the BCS theory. In particular, [Formula: see text] and [Formula: see text] for [Formula: see text].

Many-Body Quantum Monte Carlo Study of 2D Materials: Cohesion and Band Gap in Single-Layer Phosphorene

Quantum Monte Carlo (QMC) is applied to obtain the fundamental (quasiparticle) electronic band gap, $\Delta_f$, of a semiconducting two-dimensional (2D) phosphorene whose optical and electronic properties fill the void between graphene and 2D transition metal dichalcogenides. Similarly to other 2D materials, the electronic structure of phosphorene is strongly influenced by reduced screening, making it challenging to obtain reliable predictions by single-particle density functional methods. Advanced GW techniques, which include many-body effects as perturbative corrections, are hardly consistent with each other, predicting the band gap of phosphorene with a spread of almost 1 eV, from 1.6 to 2.4 eV. Our QMC results, from infinite periodic superlattices as well as from finite clusters, predict $\Delta_f$ to be about 2.4 eV, indicating that available GW results are systematically underestimating the gap. Using the recently uncovered universal scaling between the exciton binding energy and $\Delta_f$, we predict the optical gap of 1.75 eV that can be directly related to measurements even on encapsulated samples due to its robustness against dielectric environment. The QMC gaps are indeed consistent with recent experiments based on optical absorption and photoluminescence excitation spectroscopy. We also predict the cohesion of phosphorene to be only slightly smaller than that of the bulk crystal. Our investigations not only benchmark GW methods and experiments, but also open the field of 2D electronic structure to computationally intensive but highly predictive QMC methods which include many-body effects such as electronic correlations and van der Waals interactions explicitly.