Electronic Properties of h-BCN-Blue Phosphorene van der Waals Heterostructures

Insight into the Mechanisms of Nitride Films with Excellent Hardness and Lubricating Performance: A Review

Transition metal nitride (TMN) films with excellent hardness and lubricating performance are versatile low dimension materials, which are widely used in various fields including industries, transportation, aerospace, and so on. This paper introduces one film design strategy and provides a review of the mechanisms for strengthening and lubricating nitride films. The design strategy refers to two aspects which determine the structures, the performance, the components, and the chemical constitutions of nitride films The strengthening mechanisms of nitride films are then illuminated in detail, including the solid solution effect, the grain size effect, the secondary phase effect, the stress or stress field effect, the template effect, and the valence electron concentration effect. Five lubricating mechanisms are next summarized, including the easy-shear nature, the tribo-chemical reactions, the lubricious fluorides, the textured contact surface, and the synergistic effect. This paper aims to give a comprehensive introduction for understanding the mechanisms of strengthening and lubrication of nitride films for students and researchers, as well as to understand the current research progress in nitride films for exploring research gaps.

Multistage Modulation Formation of Hydrophilic-Hydrophobic Boron Carbon Nitride Nanomaterials

Boron carbon nitride (BCN) ternary compounds are attractive due to their wide applications in adsorption, catalysis, protective coatings, etc. A simple way is provided to synthesize BCN materials with multistage modulation of hydrophilic-hydrophobic properties. Hydrophilic BCN nanoparticles with a contact angle of 31° and nearly superhydrophobic BCN sheets with a contact angle of 145° are obtained. The participation of a CuO additive in the synthesis process has the role of tuning morphologies, components, and properties of BCN materials. The addition of CuO would improve the hydrophobicity of BCN due to its microstructure with enhanced surface roughness. The interaction between melamine and boric acid on the surface of CuO(111) is investigated by first-principles calculations based on density functional theory (DFT). The tuned BCN materials have different photoelectric properties also, and their performance as photocatalysts has been verified in photocatalytic reactions for hydrogen from water. The achieved uniform hydrophilic BCN nanoparticles and hydrophobic BCN sheets have the potential for further practical applications.

Strain Effects on the Electronic and Optical Properties of Blue Phosphorene

Monolayer blue phosphorene (BlueP) systems were investigated under biaxial strain range from −10% to +10%. All these systems exhibit excellent stability, accompanying changes in the electronic and optical properties. BlueP becomes metallic at −10% strain and transforms into a direct semiconductor at 10% strain while maintaining indirect semiconductor behaviors at −8% to +8% strain. The bandgap of BlueP decreases linearly with strain, and tensile strain exhibits a more moderate bandgap modulation than compressive strain. The real part of the dielectric function of BlueP is enhanced under compressive strain, while the optical absorption in the visible and the infrared light regions increases significantly under tensile strain. The maximum absorption coefficient of 0.52 ×105/cm occurs at 530 nm with the 10% strain. Our analysis indicates that the semiconductor–metal transition and the indirect–direct bandgap transition are the competition results of the energy states near the Fermi level under a massive strain. The potent compressive strain leads the py orbitals of the conduction band to move downward and pass through the Fermi level at the K point. The robust tensile strain guides the energy states at the Γ point to approach the Fermi level and become the band edges. Our results suggest that the energy storage capacity of BlueP can be significantly improved by compressive strain, while the visible light photocatalytic performance is enhanced by tensile strains of less than 8%. Our works provide a reference for the practical applications of BlueP in photocatalyst, photovoltaic cells, and electronic devices.

Computational study of electronic properties of X-doped hexagonal boron nitride (h-BN): X = (Li, Be, Al, C, Si)

The structural and electronic properties of h-BN sheet implanted with X atoms (X = lithium (Li), beryllium (Be), aluminum (Al), carbon (C), and silicon (Si)) have been investigated to tune its band gap to amend its insulating behavior toward semiconducting material employing density functional theory (DFT). It has been observed that on replacing nitrogen or boron (N/B) atom with impurity atom, several impurity levels appear in band gap dividing big gap into small energy gaps, albeit to a different extent, depending upon the dopant element and substitutional site. The lowest value of band gap falls as low as 2.27 eV as compared to 4.63 eV of pristine h-BN in addition to the appearance of states at the Fermi level. Additionally; geometrical, interaction of foreign elements with the host material, and stability issues are discussed. These results are affable for its usage in transistor-based devices and to explore its new applications in high-power electronic and optoelectronic devices.

Two-Dimensional As/BlueP van der Waals Hetero-Structure as a Promising Photocatalyst for Water Splitting: A DFT Study

Constructing van der Waals (vdW) hetero-structure by stacking different two-dimensional (2D) materials has become an effective method for designing new-type and high-quality electronic and optoelectronic nano-devices. In this work, we designed a 2D As/BlueP vdW hetero-structure by stacking monolayer arsenene (As) and monolayer blue phosphorous (BlueP) vertically, which were recently implemented in experiments, and investigated its structural, electronic, and photocatalytic water splitting properties by using the standard first principles calculation method with HSE06 hybrid exchange-correlation functional. Numerical results show that the As/BlueP vdW hetero-structure is structural robust, even at room temperature. It presents semi-conducting behavior, and the conduction band minimum (CBM) and the valence band maximum (VBM) are dominated by BlueP and As, respectively. The typical type-II band alignment predicts the potential application of the hetero-structure in highly efficient optoelectronics and solar energy conversion. Moreover, the CBM and the VBM straddle the redox potentials of water in acid environment, predicting the possibility of the As/BlueP hetero-structure as a 2D photocatalyst for water splitting. When an in-plane strain is applied, the band edges and, further, the optoelectronic properties of the hetero-structure can be effectively tuned. Especially, when tensile strain is equal to 4.5%, the optical absorption spectrum is effectively broadened in a visible light region, which will largely improve its photocatalytic efficiency, although the pH value of the solution range reduction. This work provides theoretical evidence that the As/BlueP hetero-structure has potential application as a 2D photocatalyst in water splitting.

Molecular doping of blue phosphorene: a first-principles investigation

Using first-principles calculations, we show that p-doped blue phosphorene can be obtained by molecular doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄-TCNQ) and 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F₆-TNAP), whereas n-doped blue phosphorene can be realized by doping with tetrathiafulvalene (TTF) and cyclooctadecanonaene (CCO). Moreover, the doping gap can be effectively modulated in each case by applying an external perpendicular electric field. The optical absorption of blue phosphorene can be considerably enhanced in a broad spectral range through the adsorption of CCO, F₄-TCNQ, and F₆-TNAP molecules, suggesting potential of the doped materials in the field of renewable energy.

Strain-enhanced properties of van der Waals heterostructure based on blue phosphorus and g-GaN as a visible-light-driven photocatalyst for water splitting

Many strategies have been developed to overcome the critical obstacles of fast recombination of photogenerated charges and the limited ability of semiconductor photocatalysts to absorb visible light. Considering all the novel properties of monolayered g-GaN and blue phosphorus (BlueP) which were revealed in recent studies, first-principles calculations were used to systematically investigate the structural stability, electronic energy, band alignment, band bending, and charge difference in the heterostructure formed by these two layered materials. The g-GaN/BlueP heterostructure is constructed by van der Waals (vdW) forces, and it possess a staggered band structure which induces electron transformation because of the different Fermi levels of the two layered materials. By aligning the Fermi levels, an interfacial electric field is built and it causes band bending, which can promote effective separation of photoexcited holes and electrons; the band-bending phenomenon was also calculated according to density functional theory (DFT). Moreover, effects of in-plane strain on the tuned bandgap, energy, and band edge were investigated, and the results show that the optical-absorption performance in the visible-light range can be improved. The findings reported in this paper are expected to provide theoretical support for the use of the g-GaN/BlueP vdW heterostructure as a photocatalyst for water splitting.

Many strategies have been developed to overcome the critical obstacles of fast recombination of photogenerated charges and the limited ability of semiconductor photocatalysts to absorb visible light.