Hexagonal Boron Phosphide Research Articles

Electronic and vibrational properties of van der Waals heterostructures of vertically stacked few-layer atomically thin MoS2 and BP

The state-of-the-art heterostructure-based devices often involve stacks of epilayers of few nanometer thick crystals. However, the ultimate limit would be a hitherto single-atomic-layer structure. Using material-by-design approach, the flexibility of two-dimensional (2D) materials could be explored to develop a multilayered artificial van der Waals (vdW) heterostructure where the synergistic coupling between the individual materials and the underlying interface creates new and novel functionalities. Herein, based on first-principles calculations, we report that vertically stacked few-layer vdW heterostructure of monolayer molybdenum disulfide (MoS2) and hexagonal boron phosphide (BP) is a strong electrically narrow direct bandgap material. More intriguingly, few-layer vdW heterostructure of monolayer MoS2 and BP exhibits superior mechanical properties. In striking contrast to heterostructures of MoS2/graphene, MoS2/WS2, and few-layer graphene, where the 2D moduli are lower than the sum of the 2D modulus of each nanosheet, the mechanical strength of few-layer hybrid vdW heterostructure of monolayer MoS2 and BP rather increased with increasing thickness. We attribute this difference to the unique interlayer and interface coupling, which affected the vibrational properties of the heterostructures including the emergence of shear and breathing phonon modes as well as the transformation of flexural phonon modes. Such superior mechanical properties could be explored for nanoelectromechanical device applications, e.g., as a nanoresonator. We demonstrate that the electronic structure could as well be tuned with both increasing numbers of monolayer stacks and defect-engineering promising for low-power applications.

Hexagonal boron phosphide as a potential anode nominee for alkali-based batteries: A multi-flavor DFT study

The adsorption of alkali atoms (Li, Na, and K) on graphene and hexagonal boron phosphide (h-BP) is studied by means of various density functionals including semi-local GGA, dispersion corrected DFT-D, meta-GGA, and many of the available non-local vdW-DF functionals. The accurate interaction energies are crucial for energy storage and battery applications as it is directly related to key properties in electrochemistry, such as storage capacities in general, and open circuit voltages (OCVs), in particular. A wider range of adsorption strength is predicted depending on the choice of non-local vdW-DF functionals. Furthermore, the performance of vdW-DF functionals was found to be independent of the choice of pseudopotentials used and especially if the choice is revPBE. Additionally, an excellent agreement is found between the Gaussian, VASP, and QE codes. Moreover, the h-BP is found to be an exceptional anode material for alkali batteries which can compete with any other available anode material. The small change in the adsorption energies as a function of increasing concentration of alkali atoms is a unique characteristic of h-BP. The exceptional 1283 mAh/g storage capacity not only for Li but in contrary with the previous study, also for Na in addition to the 642 mAh/g for K at vdW-DF/DZP level makes it a prominent candidate to be used as anode material. The average open circuit voltage for Li, Na, and K was also found to be in superb range. However, the values are found to be sensitive to the choice of functional, and in some cases, the storage capacity can be predicted as high as twice of the actual values. Therefore, the accurate description of the interaction is crucial and this study can be used to further refine the non-local DFT functionals. Moreover, by virtue of these properties, h-BP can be the best choice to be used as an anode material not only in LIBS but also in SIBs and KIBs.

Tuning Electronic Properties of Monolayer Hexagonal Boron Phosphide with Group III–IV–V Dopants

An extensive study on doping of two-dimensional (2D) hexagonal boron phosphide (h-BP) which is a direct band gap semiconductor was performed by using ab initio methods based on spin-polarized density functional theory. The interaction of group III–IV–V elements with h-BP is explored, considering both adsorption and substitution cases, and the resulting structural and electronic properties are examined. The variation of adsorption (substitution) energies and band gap values are systematically analyzed and trends are identified. Upon adsorption, the most of the elements bound on top of P atom forming dumbbell geometry which generates characteristic spin-polarized impurity states. The substitution of B or P by group III–IV–V elements can produce extra electrons/holes which lead to n-type and p-type doping for adequate cases. Additionally, doping can further generate impurity resonant states. Functionalization of h-BP with adatoms can tune the electronic structure and would be useful for nanoelectronic applic...

First-Principles Prediction of the Electronic Structure and Carrier Mobility in Hexagonal Boron Phosphide Sheet and Nanoribbons

Using density functional theory coupled to the Boltzmann transport equation with relaxation time approximation, we study the electronic structure and carrier mobility of graphene-like hexagonal boron phosphide (h-BP) monolayer and H-terminated armchair boron phosphide nanoribbons (ABPNRs). Our results show that the carrier mobility can reach over 104 cm2 V–1 s–1 for electron and 5 × 103 cm2 V–1 s–1 for hole in monolayer sheet. The carrier mobility in the ABPNRs is in the range of 103 to 104 cm2 V–1 s–1, and we find that the width of nanoribbon plays an important role in tuning the polarity of the carrier transport, which exhibits a distinct 3p (p is a positive integer) alternating behavior. The staggering oscillating behavior of mobility should be attributed to different bond characteristics of the edge states in the ABPNRs. Moreover, the H-terminated zigzag boron phosphide nanoribbons (ZBPNRs) have the characteristics of p-type semiconductors in electrical conduction, and the carrier mobility is increase...

Strain tunable electronic and magnetic properties of pristine and semihydrogenated hexagonal boron phosphide

Tunable electromagnetic properties of pristine two-dimensional boron phosphide (h-BP) nanosheet and its semihydrogenated structure were studied by density functional theory computations. In sharp contrast to previously reported tensile strain-induced red shift in two-dimensional semiconductors, the direct gap of h-BP undergoes blue shift under biaxial tensile strain. Once semihydrogenated, the h-BP not only transform from the nonmagnetic semiconductor into metal which is spin-resolved but also exhibits linear response between the magnetic moment and biaxial strain with a slope up to 0.005 μB/1%. These findings provide a simple and effective route to tune the electronic and magnetic properties of h-BP nanostructures in a wide range and should inspire experimental enthusiasm.

Spin-dependent transport properties of an armchair boron-phosphide nanoribbon embedded between two graphene nanoribbon electrodes

Using non-equilibrium Green׳s function and ab initio calculations we investigate structural, electronic, and transport properties of a junction consisting of armchair hexagonal boron phosphide nanoribbon (ABPNR) contacted by two semi-infinite electrodes composed of armchair graphene nanoribbons (AGNRs). We consider three different configurations including the pristine AGNR–BP–GNR and substitutions for Iron atoms, namely on phosphorus and boron atoms at one edge of the BP nanoribbon. The spin current polarization in all these cases is extracted for each structure and bias. Such hybrid system is found to exhibit not only significant spin-filter efficiency (SFE) but also tunable negative differential resistance (NDR).

Theoretical Study on a Stable Structure and Hydrogen Adsorption of Hexagonal Boron Phosphide based on Density Functional Theory

A stable structure of hexagonal boron phosphide (BP) is theoretically studied using density functional theory and compared with that of hexagonal boron nitride (BN). In the case of BN, the stable structure is planar and the electron density of N is much higher than that of B, while in the case of BP, the stable structure is nonplanar and the electric charge is small. In the case of BP, the energy level of the lowest unoccupied molecular orbital (LUMO) is very low. Hydrogen adsorption on the boron and phosphine of BP is very exothermic. Stabilization is larger on boron than on phosphine. The second hydrogen adsorption is more exothermic than the first hydrogen adsorption. A nonplanar stable structure and high reactivity are considered to make hexagonal BP unstable.