AbstractThis paper discusses the study of the structural and electronic properties of a mixture hexagonal boron nitride with phosphorene nanocomposite utilizing ab initio density functional calculations. The paper reports that the association between the hexagonal boron nitride and phosphorene is overwhelmed by the feeble van der Waals collaboration, with their own inherent electronic properties safeguarded. Moreover, the nanocomposite band gap is reliant on the interfacial separation. The review could reveal insight into the plan of new gadgets in view of van der Waals heterostructure.IntroductionLiquid exfoliation and mechanical exfoliation techniques 1-3 have been employed in the separation of two dimensional layered substances with weak interlayer van der waals interaction. A typical example of such substances are hexagonal boron nitride (h-BN) and phosphorene(P). Due to the electronic characteristics and their extensive applications of the two dimensional (2D) layered materials many researchers have been attracted to them 4-9.
h-BN is characterized by large band gap, a property of typical insulators 10-12. This property has limited h-BN in the tuning of the source drain current by applying gate voltage. For this reason h-BN has not been exploited in channel material in field effect transistor fabrication. The high degree of purity, superior thermal and chemical stability of h-BN has made it a suitable dielectric candidate for the combination with graphene or graphene like 2D crystal leading to creation of a heterostructure.Phosphorene is another stable element2D monolayer apart from graphene. The material is characterized by a unique band structure whose anisotropic mass is high and its electronic property can be tuned through straining and the electric field. As a result of these a sequence of transitions among directs semiconductor, indirect semiconductor, semimetal as well as metals 13-17.
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At the temperature of the room, the new layer material charge carrier mobility is at high level. The material band gap varies with the number of layers ranging from 0.31ev for the bulk black phosphorous and 1.51ev for monolayered material 18. At ambient conditions despite of the promising characteristics of phosphorene, phosphorous get diffracted via oxidation process 19.
For this reason researchers have tried to work in order to overcome the limitation. Among many methods that have been considered to overcome the limitation alignment of the vertical heterostructure on 2D van de waals materials has been proposed 20. It has been augured that assembling of different layered materials together contributes immensely in preserving their properties.Despite of the several researchers having been carried out their lies inadequate systematic studies on the effect of the BN monolayer capping on phosphine. This report extensively covers the protection ofphosphorene by application of the BN layer. This in return protects its degradation. This is carried out by use of the first principle.Computation modelThe first principle study carried out using ab initio simulation is reported.
In this report the approach is based on the density function theory (DFT) as implemented by vasp 22, 23. The employment of Perdew-Burk-Erzerhof is done in order to treat the ion-electron interaction 24, 25. 500ev has been set as the cut-off energy of the plane waves and the accounting for the dispersion force between the layers van der waals correction function OptB88-vdw have been adapted 26, 27.To hinder the interaction between the adjacent sheets the vacuum space along z-direction was approximately 15 A?. Whereas the atomic position and the lattice constant were relaxed to a residual force less than 0.005ev/A? and the sum of the energy charge less than eV.
To obtain an accurate band structure the screened HSE06 has been adapted 28. The stability of the heterostructure was assessed by calculating the binding energy per p atoms as in the expression below. ) (1)Where the parameters in equation (1) represent is the total energy of the heterostructure, and is the energies of the monolayer phosphorene and BN, respectively, and is the number of phosphorene atoms in the unit cell.Results and DiscussionA bilayer P/BN heterostructure was built by combining a 3 1 supercell of phosphorene with 12 P molecules and a 4 1 primitive orthorhombic cell of one BN layer with 8 B particles and 8 N atoms. The enhanced lattice constants of phosphorene are 3.30 A? and 4.
62 A? along the x and y axis. For BN, the edge length of the fundamental hexagon is 2.51 A.? Since the electronic properties of phosphorene are sensitive to the strain,19 phosphorene lattice value is maintained. Sketching of the BN framework is done to in order to compensate for the mismatch of the lattice. The supercell of the heterojunction is assigned 9.72 A? and 4.
54 A? along the x and y directions respectively. A similar methodology was utilized in the past investigations of hybrid layers 21. A cross section crisscross of around 3.3% compressive strain along the x heading and 4.4% malleable strain along the y bearing happens in BN, and no noteworthy change is seen in its electronic structure. To acquire the harmony geometry, optimization of the formed structure utilizing different beginning places of the phosphorene with respect to the BN one.Fig. 1.
(color online) (a) Top and side views of P on top of BN. The dark-magenta, light-pink, and blue balls represent phosphorus, boron, and nitrogen atoms, respectively. (b) Evolution of the total energy as a function of the displacement d of the phosphorene layer relative to BN, taking the origin at the lowest energy configuration. (c) Binding energy as a function of the distance dP/BNThe stable configuration of P/BN stacked in the AB design is illustrated in Fig.
1(a). Beginning from the setup, phosphorene is dislodged with respect to the BN layer via limited sums dx (or dy) to additionally affirm the arrangement. Figure 1(b) demonstrates the evolution of the total energy difference (DE) as a component of d.
The altering of energy along the y direction is articulated, and DE is relatively autonomous of the relative position between the P and BN layers along the x direction. In addition, since the binding energy contrast for the relocations is at a range of 1% which is very minimal, it might be conceivable that the phosphorene is caught in a position near the lowest energy arrangement amidst the development procedure. For a few displacements along the x and y directions that is dx and dy respectively, ascertaining the relating electronic structure and contrast and that at the harmony position as illustrated in Fig.
2. Insignificant change is watched, along these lines we concentrate on the most stable configuration in the accompanying substance.Fig. 2. (Color online) Band structures (upper panel) and atomic structures of P/BN (lower panel) for (a) equilibrium configuration; (b) dx = 0.5 A?; dy = 0.0 A;? (c) dx = 0.5 A?, dy = 0.
5 A? and (d) dx = 1.0 A?, dy = 0.0 A?. The red dashed lines are drawn as a guide with respect to the equilibrium configuration in panel (a).The binding energy of the intersection is computed to be 84 meV with a balance separation of 3.49 A,? as in Fig.
1(a). This esteem has an indistinguishable request of extent from that in other van der Waals systems, for example, bilayer graphene (50 meV), graphite (61 meV), and mass hexagonal boron nitride (65 meV)46. The bond angle and bond length in the P/BN heterostructure framework are nearly the same as those observed in a confined individual layer, which suggests that no covalent bond shapes in the intersection and the weak vdW between activities is ruled in the heterostructure. In Fig. 3(a), we display the band structures of the P/BN intersection, the perfect phosphorene, and the BN monolayer. The forbidden band gap of phosphorene is 1.59 eV and the BN monolayer has a circuitous band gap of 5.
69 eV with HSE06, which are in great concurrence with the past computations 13, 29. The feeble collaboration amongst phosphorene and BN exclusively brings about decreasing a band gap by a value of 0.07 eV, the states of the valence band most extreme (VBM) and the conduction band least (CBM) are nearly the same as those of a separated phosphorene layer.In this way, the electrical transport conduct of the P/BN heterostructure will in any case be administered by the phosphorene. The projected densities of states (PDOS) for the P/BN heterostructure are illustrated in Fig.
3(b). For the intersection, the states around the Fermi level are contributed totally by the 3p states of the P atoms, while the contributions of the B and N molecules are a long way from the Fermi level, outside the energy locale 1.0 eV, 4.7 eV.
Accordingly, we suggest that the electronic properties of the phosphorene are protectedFig. 3. (Color online) (a) Band structures of P/BN (black), pristine phosphorene (red), and BN monolayer (blue). (b) Projected density of states of P/BN heterostructure.The charge move in the intersection has also been analyzed. Figure 4 demonstrates the planar middle value of differential charge density along the course typical to the intersection, and the decomposed charge densities of VBM and CBM both situating at the G point. It can be observed that the BN layer gives electrons to the phosphorene, demonstrating p-doping in the BN layer and n-doping in the phosphorene.
The exchanged charge is gotten by the expression DQ (z) = R z ¥ r (z0) dz0and the computed esteem value is 0.037e. From the charge thickness plots in Figs. 4(a) and 4(c), it is certain that the charge of VBM and CBM primarily appropriates at the more electronegative P atom, exhibiting that the electronic structure of the phosphorene is unimportantly influenced by the BN sheet, and the collaboration between the phosphorene and BN is extremely frail.Fig. 4. (Color online) Decomposed charge distributions of (a) CBM and (c) VBM in the yz plane for the P/BN heterostructure.
The yellow represents the charge distributions of CBM and VBM with an iso valueof 0.01 e/A?3. (b) Planar-averaged differential charge density Dr(z) (black) and the amount of transferred charge DQ(z) (blue) in the hybrid P/BN nanocomposite at equilibrium distance in the z direction.The study demonstrated the tunable band gap in P/BN by fluctuating the interlayer separation, as plotted in Fig. 5(a).
The band gap increased from 0.67 eV to 1.36 eV (GGA) as the interfacial distance diminishes from 4.5 A? to 2.7 A,? which demonstrates the tunability for application in nanoelectronics. Figure 5(b) presents the plane arrived at the midpoint of electrostatic possibilities of the nanocomposite at various interfacial separations.Fig. 5.
(Color online) (a) The band gap of the P/BN heterostructure as a function of the interfacial distance. The BN layer is fixed and only the phosphorene layer is moved away from the BN layer. The red dot represents the equilibrium position. (b) Plane-averaged electrostatic po-tentials of P/BN at different interfacial distances dP/BN (A)?As the interlayer separation distance diminished, the expanded connection between the BN and P layers upgraded the charge transfer 30, 31. While as the interfacial distance increased, the vitality level of BN lessens marginally and the tunneling vitality obstruction at the P/BN interface for electrons would increase 32. The potential drop over the intersection was around 3.86 V.
Such a huge potential contrast implies a solid electrostatic field over the interface, which may clearly affect the bearer elements and charge infusion if the BN is filled in as the anode.ConclusionA review of the structural and electronic properties of a hybrid P/BN nanocomposite by utilizing first-principles calculation has been reported in this paper. The review demonstrates that there exists weak interaction between phosphorene with the BN sheet by means of vdW. This interaction protects theirelectronic properties. In addition, the variety of the interlayer separation could prompt tunable band holes in the hybrid P/BN nanocomposite. The redistribution of the electrostatic potential over the interface recommends that BN can fill in as a dynamic layer to tune the transporter progression of the phosphorene.
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