Electro-Optical Properties of Monolayer and Bilayer Pentagonal BN: First Principles Study

Structural superlubricity at the interface of penta-BN2

Two-dimensional (2D) materials have been widely used as lubricants due to their weak interlayer interaction and low shear resistance for interlayer sliding. Composed entirely of five-membered rings, penta-BN2 monolayer has excellent thermal and mechanical stability, higher hardness and a negative Poisson's ratio. In this work, we investigate the frictional properties at both the commensurate and incommensurate contacting interfaces of penta-BN2 by adopting the molecular dynamics (MD) simulation method. Our calculations demonstrate robust superlubricity at the incommensurate contacting interface of penta-BN2. The ultra-low friction is explained by the potential energy surface (PES) fluctuations, interlayer binding energy and out-of-plane motion amplitude of the sliding layer. In addition, our calculations show that the anisotropy of friction at the commensurate contacting interface is more obvious compared with that at the incommensurate contacting interface. Finally, the influences of the size of the Moiré pattern, normal force, temperature and sliding velocity on the friction are examined. Our results show that 2D penta-BN2 is a promising solid lubricant, enriching the family of 2D lubrication materials.

Engineering van der Waals Materials for Advanced Metaphotonics

The outstanding chemical and physical properties of 2D materials, together with their atomically thin nature, make them ideal candidates for metaphotonic device integration and construction, which requires deep subwavelength light-matter interaction to achieve optical functionalities beyond conventional optical phenomena observed in naturally available materials. In addition to their intrinsic properties, the possibility to further manipulate the properties of 2D materials via chemical or physical engineering dramatically enhances their capability, evoking new science on light-matter interaction, leading to leaped performance of existing functional devices and giving birth to new metaphotonic devices that were unattainable previously. Comprehensive understanding of the intrinsic properties of 2D materials, approaches and capabilities for chemical and physical engineering methods, the resulting property modifications and novel functionalities, and applications of metaphotonic devices are provided in this review. Through reviewing the detailed progress in each aspect and the state-of-the-art achievement, insightful analyses of the outstanding challenges and future directions are elucidated in this cross-disciplinary comprehensive review with the aim to provide an overall development picture in the field of 2D material metaphotonics and promote rapid progress in this fast emerging and prosperous field.

Hydrogen Storage in Bilayer Hexagonal Boron Nitride: A First-Principles Study

Using first-principles calculations, we report on the structural and electronic properties of bilayer hexagonal boron nitride (h-BN), incorporating hydrogen (H2) molecules inside the cavity for potential H2-storage applications. Decrease in binding energies and desorption temperatures with an accompanying increase in the weight percentage (upto 4%) by increasing the H2 molecular concentration hints at the potential applicability of this study. Moreover, we highlight the role of different density functionals in understanding the decreasing energy gaps and effective carrier masses and the underlying phenomenon for molecular adsorption. Furthermore, energy barriers involving H2 diffusion across minimum-energy sites are also discussed. Our findings provide significant insights into the potential of using bilayer h-BN in hydrogen-based energy-storage applications.

A method to restore the intrinsic dielectric functions of 2D materials in periodic calculations

Previous calculations of the dielectric and optical properties of 2D materials often overlooked or circumvented the influence of vacuum spacing introduced in periodic calculations, which gave rise to mispredictions of the intrinsic properties of 2D materials or merely qualitative results. We first elucidated the relationship between the vacuum spacing and the dielectric and optical properties of 2D materials in periodic calculations, and then formulated an effective method to accurately predict the dielectric and optical properties of 2D materials by restoring the intrinsic dielectric functions of 2D materials independent of the additional vacuum spacing. As examples, the intrinsic dielectric and optical properties of ultrathin hexagonal boron nitride (h-BN) and molybdenum sulphide (MoS₂) from a monolayer to a pentalayer, including dielectric functions, optical absorption coefficients, refraction indexes, reflectivities, extinction coefficients, and energy loss functions, have been calculated by our method. Our calculations reveal that the out-of-plane optical dielectric constants, static refraction indexes, and static reflectivities of 2D h-BN and MoS₂ increase as the number of layers increases, while the in-plane counterparts remain unchanged. The excitonic frequency-dependent optical properties of h-BN and MoS₂ from a monolayer to bulk are also calculated by solving the Bethe-Salpeter equation and they show strong anisotropy. The present method shows better agreement with the experimental results compared to previous calculations and demonstrates enormous potential to investigate the dielectric and optical properties of other 2D materials extensively and quantitatively.

Enhanced H2 Storage Capacity of Bilayer Hexagonal Boron Nitride (h-BN) Incorporating van der Waals Interaction under an Applied External Electric Field

Lightweight two-dimensional materials are being studied for hydrogen storage applications due to their large surface area. The characteristics of hydrogen adsorption on the h-BN bilayer under the applied electric field were investigated. The overall storage capacity of the bilayer is 6.7 wt % from our theoretical calculation with E _ads of 0.223 eV/H₂. The desorption temperature to remove the adsorbed H₂ molecules from the surface of the h-BN bilayer system in the absence of an external electric field is found to be ∼176 K. With the introduction of an external electric field, the E _ads lies in the range of 0.223-0.846 eV/H₂ and the desorption temperature is from 176 to 668 K. Our results show that the external electric field enhances the average adsorption energy as well as the desorption temperature and thus makes the h-BN bilayer a promising candidate for hydrogen storage.

Plasma-Assisted Synthesis of Platinum Nitride Nanoparticles under HPHT: Realized by Carbon-Encapsulated Ultrafine Pt Nanoparticles

Noble metal nitrides (NMNs) have important theoretical significance and potential application prospects due to their high bulk modulus and remarkable electrical properties. However, NMNs can only be synthesized under extreme conditions of ultrahigh pressure and temperature, and nanoscaled NMNs have not been reported. In this work, as typical NMNs, PtN_x nanoparticles were synthesized at 5 GPa and 750 K by the method of plasma-assisted laser-heating diamond anvil cell. The significantly reduced synthesis condition benefited from the ingenious design of the precursor and the remarkable chemical activity of the ultrafine Pt nanoparticles. This study, combining nanomaterials with high-pressure and -temperature (HPHT) techniques, provides a novel process for the preparation of NMN nanomaterials, and a new direction for the synthesis of superhard materials.