Twist angle and electric gating controllable electronic structure of the two-dimensional stacked BP homo-structure.

The boron phosphide (BP) van der Waals (vdW) homostructure is designed to construct high-performance nano-optoelectronic devices due to its distinctive photoelectric properties. Using density functional theory, the electronic properties of twisted and untwisted BP bilayer structures are systematically calculated. We found that the 0° structure is a direct band gap semiconductor with a type II band alignment, the carrier mobility of which is increased to 104, and its photoelectric conversion efficiency is 17.3%. By analyzing the band structure and exciton binding energy calculated at 0° under an electric field, it is further found that 0° is a superior photoelectric material. As for the twist BP bilayer, the band gap changes with torsional structures under the applied electric field, which generates the Stark effect. The twist angles of bilayer BP, specifically 13.17°, 21.79°, 38.21°, and 46.83°, always maintain a direct band gap under the influence of an electric field. While 60° is an indirect band gap, the structure exhibits high resistance to the electric field. Our results reveal that bilayer BP is a potential application prospect in photovoltaic and optoelectronic fields and can provide more insights into optoelectronic devices.

First-principles study on CO oxidation on CuO(111) surface prefers the Eley-Rideal or Langmuir-Hinshelwood pathway.

Using the first-principles approach, we investigated the electronic and chemical properties of cupric oxide CuO (110) and CuO (111) and substantiated their catalytic activity toward CO oxidation. It is found that CuO (111) surface is more stable than the CuO (110) surface. We firstly study that adsorption of CO and O2on perfect, oxygen vacancies and Cu-anchored CuO (111) surface. It is found that adsorption of CO and O2molecules are chemical. Then we selected the most stable adsorption structure of CO/O2to investigated the CO oxidation mechanism on different surface, here we choose to study the Langmuir-Hinshelwood (LH) mechanism and Eley-Rideal (ER) mechanism. The results show that perfect and OvacancyCuO (111) surface is more inclined to LH mechanism, while the Cu-anchored CuO (111) surface is more inclined to ER mechanism. The results show that CuO catalyst is very effective for CO oxidation. Our work provides a deep understanding for the search of economical and reasonable CO oxidation catalysts.

A type-II NGyne/GaSe heterostructure with high carrier mobility and tunable electronic properties for photovoltaic application.

The two-dimensional heterostructures with type-II band alignment and super-high carrier mobility offer an updated perspective for photovoltaic devices. Here, based on the first-principles calculation, a novel vertical NGyne/GaSe heterostructure with an intrinsic type-II band alignment, super-high carrier mobility (104cm2V-1s-1), and strong visible to ultraviolet light absorption (104-105cm-1) is constructed. We investigate the electronic structure and the interfacial properties of the NGyne/GaSe heterostructure under electric field and strain. The band offsets and band gap of the NGyne/GaSe heterostructure can be regulated under applied vertical electric field and strain efficiently. Further study reveals that the photoelectric conversion efficiency of the NGyne/GaSe heterostructure is vastly improved under a negative electric field and reaches up to 25.09%. Meanwhile, near-free electron states are induced under a large applied electric field, leading to the NGyne/GaSe heterostructure transform from semiconductors to metal. Our results indicate that the NGyne/GaSe heterostructure will have extremely potential in optoelectronic devices, especially solar cells.

Ferromagnetism and optical properties of SnS2 doped with two impurities: first-principles calculations.

Based on the first principles of the GGA method, the magnetic and optical properties of intrinsic SnS2; Fe, Cr mono-doped SnS2; and (Fe, Cr) co-doped SnS2 are studied. The results show that the ground states of Fe, Cr mono-doped SnS2 are spin polarized, and the magnetic moments caused are 1.99 µB and 3.00 µB, respectively. The magnetic moment of Fe mono-doped SnS2 is mainly produced by Fe:3d orbitals, and the magnetic moment of Cr mono-doped SnS2 is mainly produced by Cr:3d and Sn:4d orbitals. We calculate that in the (Fe, Cr) co-doped SnS2 system, Fe, Cr and the adjacent S atoms form a strong hybrid, that is, the closest S atom between Fe and Cr atoms mediates the spin polarization and ferromagnetic (FM) coupling. This promotes the formation of a Fe:3d-S:3p-Cr:3d coupling chain, so that (Fe, Cr) co-doped SnS2 obtains FM stability. In addition, with the introduction of Fe and Cr atoms, the absorption coefficient is the largest in the long-wavelength infrared region of 0.23-1.63 eV. This shows that Fe and Cr doping can make up for the lack of absorption of intrinsic materials in the infrared region. In summary, Fe, Cr doped SnS2 dilute magnetic semiconductors may be a good candidate in the field of spintronic devices.