Electronic Properties of Transferable Atomically Thin MoSe2/h-BN Heterostructures Grown on Rh(111)

Electronic Properties of Vertically Stacked h-BN/B1-xAlxN Heterojunction on Si(100)

Hexagonal boron nitride (h-BN) exhibits a dangling bond-free layered structure and ultrawide band gap, which is apt to integrate with other semiconductors to form a heterojunction. Particularly, heterojunction structure is the main impetus for h-BN to broaden the horizon on deep ultraviolet optoelectronic and photovoltaic applications. Here, a series of h-BN/B_1-xAl_xN heterojunctions with different Al components were fabricated by radio frequency (RF) magnetron sputtering. The performance of h-BN/B_1-xAl_xN heterojunction was measured via I-V characteristic representation. The sample of h-BN/B_0.89Al_0.11N heterojunction was the best one due to the high lattice matching. Moreover, a type-II (staggered) band alignment was formed in this heterojunction which was elucidated by X-ray photoelectron spectroscopy (XPS). The calculated valence band offset (VBO) and conduction band offset (CBO) of h-BN/B_0.89Al_0.11N are 1.20 and 1.14 eV, respectively. The electronic properties and formation mechanism of h-BN/B_0.89Al_0.11N heterojunction were further studied by density functional theory (DFT) calculation. The existence of a built-in field (E_in) was confirmed, and the E_in direction was from the BAlN side to h-BN side. The staggered band alignment was further verified in this heterojunction, and an Al-N covalent bond existed at the interface from calculated results. This work paves a pathway to construct an ultrawide band gap heterojunction for the next-generated photovoltaic application.

Suppressing Li Dendrite Puncture with a Hierarchical h-BN Protective Layer

Lithium metal has been perceived as an extremely attractive anode due to its superior energy density and low redox potential. However, great challenges affiliated with the operating security of Li metal batteries (LMBs) posed by growing Li dendrites hamper the widespread application of rechargeable LMBs. In this study, hierarchical hairball-like boron nitride (h-BN) was fabricated on a Li metal anode using the pulsed laser deposition (PLD) method. The chemically inert and mechanically robust dielectric h-BN coating on the Li anode can act as an interfacial layer conducive to enhancing the stability and extending the battery lifetime of LMBs by suppressing the formation and propagation of dendrites during the recurrent plating and stripping process. Moreover, the h-BN layer favors the drift of Li ions and mitigates electrolyte depletion, therefore demonstrating a reduced polarization in the voltage profiles, which further facilitates the uniform deposition of Li ions during battery operation. As proof, the Li/BN || BN/Li symmetrical cells can circulate steadily for 1800 h with no observable polarization at constant current density. Thus, the three-dimensional h-BN interface layer is efficacious for Li dendrite suppression during the practical application of LMBs, and it may also be promising for tackling dendrite issues in other metal ion battery systems.

Electronic and optical properties of two-dimensional GaN/ZnO heterojunction tuned by different stacking configurations

Two-dimensional (2D) semiconductors show novel electronic and optoelectronic applications due to their excellent performance. The van der Waals (vdW) heterostructures are also a new method for the design of low dimensional optoelectronic devices. However, their fundamental electronic structure and optical properties are sensitive to stacking configurations. Herein, we perform systematic first-principle calculations for monolayer GaN and ZnO by six different stacking styles. The results suggest that the bonding type and stability vary with the stacking method. Chemical bonding and vdW interaction are respectively observed in different models. However, the carrier mobilities for different models are all enhanced after integration. Both type I and II band alignment can be generated from different stacking models. The optical properties suggest high absorptivity in the solar-blind region. This study is an early stage for the design and synthesis of photodetectors or solar cells based on 2D GaN/ZnO heterojunctions and also opens a far-ranging research interest in optoelectronic materials and devices with more advanced semiconductor materials.

2D III-Nitride Materials: Properties, Growth, and Applications

2D III-nitride materials have been receiving considerable attention recently due to their excellent physicochemical properties, such as high stability, wide and tunable bandgap, and magnetism. Therefore, 2D III-nitride materials can be applied in various fields, such as electronic and photoelectric devices, spin-based devices, and gas detectors. Although the developments of 2D h-BN materials have been successful, the fabrication of other 2D III-nitride materials, such as 2D h-AlN, h-GaN, and h-InN, are still far from satisfactory, which limits the practical applications of these materials. In this review, recent advances in the properties, growth methods, and potential applications of 2D III-nitride materials are summarized. The properties of the 2D III-nitride materials are mainly obtained by first-principles calculations because of the difficulties in the growth and characterizations of these materials. The discussion on the growth of 2D III-nitride materials is focused on 2D h-BN and h-AlN, as the developments of 2D h-GaN and h-InN are yet to be realized. Therefore, applications have been realized mostly based on the 2D h-BN materials; however, many potential applications are cited for the entire range of 2D III-nitride materials. Finally, future research directions and prospects in this field are also discussed.

Ultrasonic-Ball Milling: A Novel Strategy to Prepare Large-Size Ultrathin 2D Materials

Large-size ultrathin 2D materials, with extensive applications in optics, medicine, biology, and semiconductor fields, can be prepared through an existing common physical and chemical process. However, the current exfoliation technologies still need to be improved upon with urgency. Herein, a novel and simple "ultrasonic-ball milling" strategy is reported to effectively obtain high quality and large size ultrathin 2D materials with complete lattice structure through the introduction of moderate sapphire (Al₂ O₃ ) abrasives in a liquid phase system. Ultimately numerous high-quality ultrathin h-BN, graphene, MoS₂ , WS₂ , and BCN nanosheets are obtained with large sizes ranging from 1-20 µm, small thickness of ≈1-3 nm and a high yield of over 20%. Utilizing shear and friction force synergistically, this strategy provides a new method and alternative for preparing and optimizing large size ultrathin 2D materials.

Effects of Se substitution and transition metal doping on the electronic and magnetic properties of a MoSxSe2-x/h-BN heterostructure

The van der Waals heterostructures created by stacking two monolayer semiconductors have been rapidly developed experimentally and exhibit various unique physical properties. In this work, we investigate the effects of Se atom substitution and 3d-TM atom doping on the structural, electronic, and magnetic properties of the MoSe2/h-BN heterostructure, by using first-principles calculations based on density functional theory (DFT). It is found that Se atom substitution could considerably enhance the band gaps of MoSe2/h-BN heterostructures. With an increase in the substitution concentration, the energy band changes from an indirect to a direct band gap when the substitution concentration exceeds a critical value. For 3d-TM atom doping, it is shown that V-, Mn-, Fe-, and Co-doped systems exhibit a half-metallic state and magnetic behavior, while there is no spin polarization in the Ni-doped case. The results provide a theoretical basis for the development of diluted magnetic semiconductors and spin devices based on the MoSxSe2-x/h-BN heterostructure.

Catalyst Proximity-Induced Functionalization of h-BN with Quat Derivatives

Inert single-layer boron nitride (h-BN) grown on a catalytic metal may be functionalized with quaternary ammonium compounds (quats) that are widely used as nonreactive electrolytes. We observe that the quat treatment, which facilitates the electrochemical transfer of two-dimensional materials, involves a decomposition of quat ions and leads to covalently bound quat derivatives on top of the 2D layer. Applying tetraoctylammonium and h-BN on rhodium, the reaction product is top-alkylized h-BN as identified with high-resolution X-ray photoelectron spectroscopy. The alkyl chains are homogeneously distributed across the surface, and the properties thereof are well-tunable by the choice of different quats. The functionalization further weakens the 2D material-substrate interaction and promotes easy transfer. Therefore, the functionalization scheme that is presented enables the design of 2D materials with tailored properties and with the freedom to position and orient them as required. The mechanism of this functionalization route is investigated with density functional theory calculations, and we identify the proximity of the catalytic metal substrate to alter the chemical reactivity of otherwise inert h-BN layers.