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Dynamically engineering bandgap in semiconductors may enable a flexible design and optimization of electronics and optoelectronics. Layered black phosphorus is a 2D semiconductor with a direct bandgap and promising device characteristics. Theoretical studies indicate that the bandgap in black phosphorus can be tuned by electrical field. Here, through designing a double-gated field-effect transistor device configuration, we experimentally demonstrate that the bandgap in few-layer black phosphorus can be dynamically continually tuned by perpendicular electrical field. With an electrical displacement field of 1 V nm−1, the detailed study indicates that the bandgap can reduce around 100 meV. The finding here should be helpful on the flexible design and optimization of black phosphorus electronics and optoelectronics, and may open up some other new possible applications.

Graphene-like hexagonal boron phosphide with its moderate band gap and high carrier mobility is considered to be a high potential material for electronics and optoelectronics. In this work, the tight-binding Hamiltonian of hexagonal boron phosphide monolayer and bilayer with two stacking orders are derived in detail. Including up to fifth-nearest-neighbor in plane and next-nearest-neighbor interlayer hoppings, the tight-binding approximated band structure can well reproduce the first-principle calculations based on the screened Heyd–Scuseria–Ernzerhof hybrid functional level over the entire Brillouin zone. The band gap deviations for monolayer and bilayer between our tight-binding and first-principle results are only 2 meV. The low-energy effective Hamiltonian matrix and band structure are obtained by expanding the full band structure close to the K point. The results show that the iso-energetic lines of maximum valence band in the vicinity of K point undergo a pseudo-Lifshitz transition from h-BP monolayer to AB_B-P or AB_B-B bilayer. The mechanism of pseudo-Lifshitz transition can be attributed to two interlayer hoppings rather than one.

Two-dimensional hexagonal boron phosphide presents great potential in applications of electronics and optoelectronics due to its high carrier mobility and moderate band gap. In this work, we investigate the effect of stress and electric field on the electronic properties of hexagonal boron phosphide layers based on first-principles calculations. We find that both the band gap and the carrier effective masses of hexagonal boron phosphide monolayer gradually increase with stress from compression to tension. As for hexagonal boron phosphide bilayer with two stacking orders (AB_B-P and AB_B-B) upon applied electric field, the band gap monotonously increases with the enhancement of electric field for AB_B-P bilayer, while it undergoes a band gap closing and reopening process for AB_B-B bilayer. We employ the tight-binding model to explain the mechanism of different band gap variations of two stacking orders with electric field. Moreover, we discuss the band gap variation of hexagonal boron phosphide bilayer with combined effect of stress and electric field. The investigation here presents an insight into the effective manipulation towards the electronic properties of hexagonal boron phosphide, which will further enable the broader applications of the hexagonal boron phosphide in modern electronic and optoelectronic fields.

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Dozens of layered V2IV2VI6 (V=P, As, Sb, Bi; IV=Si, Ge, Sn, Pb; VI=S, Se, Te) materials are investigated, several of which have been successfully synthesized in experiment. Among them, nine strong topological insulators (TIs), two strong Z2 topological metals (TMs), and nearly twenty trivial insulators are predicted at their equilibrium structures. The TIs are in the (1;111) topological class, with energy gaps ranging from 0.04 to 0.2 eV. The strong Z2 TMs and the trivial insulators belong to the (1;111) and (0;000) topological classes, respectively. Small compressive strains easily turn some of the trivial insulators into strong TIs. This study enriches not only the family of topological materials but also the family of van der Waals layered materials, providing promising candidates for the future spintronic devices.

A monolithic sponge catalyst composed of amorphous cobalt boride nanoparticles homogeneously deposited on the fibres of commercial polyvinyl formal (PVFM) sponge is developed for hydrolysis of NaBH4. Hydrolysis of NaBH4...

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