Synergistic Behavior of Tubes, Junctions, and Sheets Imparts Mechano-Mutable Functionality in 3D Porous Boron Nitride Nanostructures

Structures, Electronic Properties, and Gas Permeability of 3D Pillared Silicon Carbide Nanostructures

Silicon carbide (SiC) is recognized as excellent material for high power/temperature applications with a wide-band gap semiconductor. With different structures at the nanosize scale, SiC nanomaterials offer outstanding mechanical, physical, and chemical properties leading to a variety of applications. In this work, new 3D pillared SiC nanostructures have been designed and investigated based on self-consistent charge density functional tight-binding (SCC-DFTB) including Van der Waals dispersion corrections. The structural and electronic properties of 3D pillared SiC nanostructures with effects of diameters and pillar lengths have been studied and compared with 3D pillared graphene nanostructures. The permeability of small gas molecules including H₂O, CO₂, N₂, NO, O₂, and NO₂ have been demonstrated with different orientations into the 3D pillared SiC nanostructures. The promising candidate of 3D pillared SiC nanostructures for gas molecule separation application at room temperature is highlighted.

Titanium-decorated boron nitride nanotubes for hydrogen storage: a multiscale theoretical investigation

A multiscale computational technique from available quantum mechanical and Molecular Dynamics (MD) codes to user-subroutine computational fluid dynamics (CFD) files was applied to the H2 adsorption of Ti-decorated (10,0) single-walled BN nanotubes (BNNTs) with B-N defects. According to density functional theory (DFT), the Ti atom adsorbed in the defect protrudes outward from the surface and does not agglomerate. The Ti/BNNT system possesses excellent affinity towards H2 molecules with thermodynamically favorable binding energies. Up to seven H2 molecules can partially attach near Ti in quasi-molecular form due to the cationic functionalized Ti and heteropolar B-N bonds at the surface. MD simulation further reveals that the seven H2 molecules are indeed physisorbed in two distinct regions near to (at ∼2 Å) and far from (at ∼4 Å) the Ti atom. The thermal properties obtained from MD simulations were utilized in the CFD code to quantify thermal energy transfer. According to CFD, the equilibrium pressure distribution for a type III H2 cylinder is initially low within its locality. The rate of change of pressure increase is quite steep as it rises due to a sudden increase in temperature upon uptake and it eventually slows down when the local temperature reaches its saturation value.

Intercalated Hexagonal Boron Nitride/Silicates as Bilayer Multifunctional Ceramics

By performing an extensive 150+ first-principles calculations, this work demonstrates how the exotic properties of emerging 2D hBN nanosheets (e.g., ultrahigh surface area, high mechanical and thermal tolerance) can be coupled strategically (via exfoliation and geometrical compatibility) with the lamellar nanostructure of calcium-silicate crystals to introduce "reinforcement" at the basal plane of materials, i.e., the smallest possible scale. Probing mechanical properties show significant enhancement in strength, toughest, stiffness and strain, providing key guidelines to intercalate a suite of emerging 2D materials in ceramics for the bottom-up design and fabrication of ultrahigh performance and multifunctional ceramic composites.

Intrinsic Size Effect in Scaffolded Porous Calcium Silicate Particles and Mechanical Behavior of Their Self-Assembled Ensembles

Scaffolded porous submicron particles with well-defined diameter, shape, and pore size have profound impacts on drug delivery, bone-tissue replacement, catalysis, sensors, photonic crystals, and self-healing materials. However, understanding the interplay between pore size, particle size, and mechanical properties of such ultrafine particles, especially at the level of individual particles and their ensemble states, is a challenge. Herein, we focus on porous calcium-silicate submicron particles with various diameters-as a model system-and perform extensive 900+ nanoindentations to completely map out their mechanical properties at three distinct structural forms from individual submicron particles to self-assembled ensembles to pressure-induced assembled arrays. Our results demonstrate a notable "intrinsic size effect" for individual porous submicron particles around ∼200-500 nm, induced by the ratio of particle characteristic diameter to pore characteristic size distribution. Increasing this ratio results in a brittle-to-ductile transition where the toughness of the submicron particles increases by 120%. This size effect becomes negligible as the porous particles form superstructures. Nevertheless, the self-assembled arrays collectively exhibit increasing elastic modulus as a function of applied forces, while pressure-induced compacted arrays exhibit no size effect. This study will impact tuning properties of individual scaffolded porous particles and can have implications on self-assembled superstructures exploiting porosity and particle size to impart new functionalities.

Asymmetric Junctions Boost in-Plane Thermal Transport in Pillared Graphene

Hybrid 3D nanoarchitectures by covalent connection of 1D and 2D nanomaterials are currently in high demands to overcome the intrinsic anisotropy of the parent materials. This letter reports the junction configuration-mediated thermal transport properties of Pillared Graphene (PGN) using reverse nonequilibrium molecular dynamics simulations. The asymmetric junctions can offer ∼20% improved in-plane thermal transport in PGN, unlike the intuition that their wrinkled graphene sheets cause phonon scattering. This asymmetric trait, which entails lower phonon scattering provides a new degree of freedom to boost thermal properties of PGN and potentially other hybrid nanostructures.

Interlaced, Nanostructured Interface with Graphene Buffer Layer Reduces Thermal Boundary Resistance in Nano/Microelectronic Systems

Improving heat transfer in hybrid nano/microelectronic systems is a challenge, mainly due to the high thermal boundary resistance (TBR) across the interface. Herein, we focus on gallium nitride (GaN)/diamond interface-as a model system with various high power, high temperature, and optoelectronic applications-and perform extensive reverse nonequilibrium molecular dynamics simulations, decoding the interplay between the pillar length, size, shape, hierarchy, density, arrangement, system size, and the interfacial heat transfer mechanisms to substantially reduce TBR in GaN-on-diamond devices. We found that changing the conventional planar interface to nanoengineered, interlaced architecture with optimal geometry results in >80% reduction in TBR. Moreover, introduction of conformal graphene buffer layer further reduces the TBR by ∼33%. Our findings demonstrate that the enhanced generation of intermediate frequency phonons activates the dominant group velocities, resulting in reduced TBR. This work has important implications on experimental studies, opening up a new space for engineering hybrid nano/microelectronics.

Oxygen- and Lithium-Doped Hybrid Boron-Nitride/Carbon Networks for Hydrogen Storage

Hydrogen storage capacities have been studied on newly designed three-dimensional pillared boron nitride (PBN) and pillared graphene boron nitride (PGBN). We propose these novel materials based on the covalent connection of BNNTs and graphene sheets, which enhance the surface and free volume for storage within the nanomaterial and increase the gravimetric and volumetric hydrogen uptake capacities. Density functional theory and molecular dynamics simulations show that these lithium- and oxygen-doped pillared structures have improved gravimetric and volumetric hydrogen capacities at room temperature, with values on the order of 9.1-11.6 wt % and 40-60 g/L. Our findings demonstrate that the gravimetric uptake of oxygen- and lithium-doped PBN and PGBN has significantly enhanced the hydrogen sorption and desorption. Calculations for O-doped PGBN yield gravimetric hydrogen uptake capacities greater than 11.6 wt % at room temperature. This increased value is attributed to the pillared morphology, which improves the mechanical properties and increases porosity, as well as the high binding energy between oxygen and GBN. Our results suggest that hybrid carbon/BNNT nanostructures are an excellent candidate for hydrogen storage, owing to the combination of the electron mobility of graphene and the polarized nature of BN at heterojunctions, which enhances the uptake capacity, providing ample opportunities to further tune this hybrid material for efficient hydrogen storage.

Dimensional Crossover of Thermal Transport in Hybrid Boron Nitride Nanostructures

Although boron nitride nanotubes (BNNT) and hexagonal-BN (hBN) are superb one-dimensional (1D) and 2D thermal conductors respectively, bringing this quality into 3D remains elusive. Here, we focus on pillared boron nitride (PBN) as a class of 3D BN allotropes and demonstrate how the junctions, pillar length and pillar distance control phonon scattering in PBN and impart tailorable thermal conductivity in 3D. Using reverse nonequilibrium molecular dynamics simulations, our results indicate that although a clear phonon scattering at the junctions accounts for the lower thermal conductivity of PBN compared to its parent BNNT and hBN allotropes, it acts as an effective design tool and provides 3D thermo-mutable features that are absent in the parent structures. Propelled by the junction spacing, while one geometrical parameter, e.g., pillar length, controls the thermal transport along the out-of-plane direction of PBN, the other parameter, e.g., pillar distance, dictates the gross cross-sectional area, which is key for design of 3D thermal management systems. Furthermore, the junctions have a more pronounced effect in creating a Kapitza effect in the out-of-plane direction, due to the change in dimensionality of the phonon transport. This work is the first report on thermo-mutable properties of hybrid BN allotropes and can potentially impact thermal management of other hybrid 3D BN architectures.