Size-dependent dynamic characteristics of graphene based multi-layer nano hetero-structures

Atomically Thin Hexagonal Boron Nitride and Its Heterostructures

Atomically thin hexagonal boron nitride (h-BN) is an emerging star of 2D materials. It is taken as an optimal substrate for other 2D-material-based devices owing to its atomical flatness, absence of dangling bonds, and excellent stability. Specifically, h-BN is found to be a natural hyperbolic material in the mid-infrared range, as well as a piezoelectric material. All the unique properties are beneficial for novel applications in optoelectronics and electronics. Currently, most of these applications are merely based on exfoliated h-BN flakes at their proof-of-concept stages. Chemical vapor deposition (CVD) is considered as the most promising approach for producing large-scale, high-quality, atomically thin h-BN films and heterostructures. Herein, CVD synthesis of atomically thin h-BN is the focus. Also, the growth kinetics are systematically investigated to point out general strategies for controllable and scalable preparation of single-crystal h-BN film. Meanwhile, epitaxial growth of 2D materials onto h-BN and at its edge to construct heterostructures is summarized, emphasizing that the specific orientation of constituent parts in heterostructures can introduce novel properties. Finally, recent applications of atomically thin h-BN and its heterostructures in optoelectronics and electronics are summarized.

Simulated mechanical properties of finite-size graphene nanoribbons

There are many simulation studies of mechanical properties of graphene nanoribbons (GNR), but there is a lack of agreement regarding elastic and plastic behavior. In this paper we aim to analyze mechanical properties of finite-size GNR, including elastic modulus and fracture, as a function of ribbon size. We present classical molecular dynamics simulations for three different empirical potentials which are often used for graphene simulations: AIREBO, REBO-scr and REAXFF. Ribbons with and without H-passivation at the borders are considered, and the effects of strain rate and different boundaries are also explored. We focus on zig-zag GNR, but also include some armchair GNR examples. Results are strongly dependent on the empirical potential employed. Elastic modulus under uniaxial tension can depend on ribbon size, unlike predictions from continuum-scale models and from some atomistic simulations, and fracture strain and progress vary significantly amongst the simulated potentials. Because of that, we have also carried out quasi-static ab-initio simulations for a selected size, and find that the fracture process is not sudden, instead the wave function changes from Blöch states to a strong interaction between localized waves, which decreases continuously with distance. All potentials show good agreement with DFT in the linear elastic regime, but only the REBO-scr potential shows reasonable agreement with DFT both in the nonlinear elastic and fracture regimes. This would allow more reliable simulations of GNRs and GNR-based nanostructures, to help interpreting experimental results and for future technological applications.