Antimonene, one of the group V elemental monolayers, has attracted intense interest due to its intriguing electronic properties. Here, we present the optical absorption properties of atomically flat antimonene for which the directional bonds between Sb atoms appear to be analogous to C–C bonds in graphene. The results, based on first-principles density functional theory calculations, predict the absorbance in multilayer antimonene to be comparable or higher than that calculated for multilayer graphene. Specifically, the IR absorption in antimonene is significantly higher with a prominent band at about 4 μm associated with the dipole-allowed interband transitions. Furthermore, a strong dependence of absorbance on topology is predicted for both antimonene and graphene which results from the subtle variations in their stacking-dependent band structures. Our results suggest multilayer antimonene to be a good candidate material for optical power limiting applications in the IR region.

Polymer composites possess an integrated combination of structures and properties associated with the host matrix and the fiber material and thus hold the potential of being high-strength materials. In general, the load transfer from the matrix to the fiber depends upon the strength of bonding at the interface, which characterizes the mechanical strength. In this work, first-principles calculations based on the density functional theory are employed to provide the molecular-level description of the interface formed by resins (i.e., diglycidyl ether of bisphenol A (DGEBA) and 4′-bismaleimidodiphenylmethane (BMPM)) or hardeners (i.e., diethyl toluene diamine (DETDA) and o,o′-diallyl bisphenol A (DABPA)) with graphene (or boron nitride (BN) monolayer). The results show that the interaction strength between a resin (or hardener) and graphene is mainly governed by the nature of bonding at the interface, and subsequently, the mechanical response follows the hierarchical order of the interaction strength at the interface; the transverse stiffness of BMPM/graphene is higher than that of DGEBA/graphene. Moreover, the change in the polarity of the surface from graphene to the BN monolayer improves the superior interfacial strength and thereby a higher transverse stiffness of both resin and hardener composites at the molecular level. These results emphasize the need to use computational modeling to efficiently and accurately determine molecular-level polymer/surface combinations that yield optimal mechanical performance of composite materials. This is especially important in the design and development of high-performance composites with nanoscale reinforcement.

Herein, we study the effects that carbon nanotubes (CNTs) have on the curing of the bismaleimide resin matrix (BMI), as well as the effects that the curing of BMI has on the CNTs, in the nanocomposites containing up to 40 wt % CNTs. Two different types of CNTs in the sheet form: unbaked and baked (termed as UB and B CNT), have been employed. Addition of only 10 wt % UB CNT (10 wt % UB − 90 wt % BMI) reduced the BMI cure temperature by up to 123 °C, compared to the cure temperature of neat BMI with no CNTs (100 wt % BMI). The 40 wt % UB − 60 wt % BMI demonstrated a 107 °C increase in the glass transition temperature, compared to the 100 wt % BMI. UB CNTs in the 10 wt % UB − 90 wt % BMI compressed upon the cure of BMI with an estimated compressive stress of 2.9 GPa while the UB CNTs in the 40 wt % UB − 60 wt % BMI were not compressed. The factors leading to these unprecedented effects have been discussed. The effect of the varying CNT content on the inter-CNT spacing and consequently the cure reactions of the BMI, compression of CNTs, and the thermomechanical properties of the nanocomposites has been discussed using an ideal CNT-BMI interaction model. Based on the thermomechanical results and the theoretical calculations, interphase thicknesses of at least 5.3 and 4 nm are estimated for the 30 and 40 wt % CNT nanocomposites, respectively. Since an optimum cure condition is critical to obtain the best mechanical properties in a CNT-BMI system, our results suggest that the optimum cure condition will likely vary for each unique CNT-BMI system. Thus, going forward, optimizing the cure conditions for each CNT-BMI system is critical in realizing the best mechanical properties from that system. Potential applications of the CNT-BMI nanocomposites include structural materials in the aerospace domain.

Graphene-based hybrid van der Waals structures have emerged as a new class of materials for novel multifunctional applications. In such a vertically-stacked heterostructure, it is expected that its mechanical strength can be tailored by the orientation of the constituent monolayers relative to each other. In this paper, we explore this hypothesis by investigating the orientation dependence of the mechanical properties of graphene/h-BN heterostructures together with that of graphene and h-BN bilayers. The calculated results simulating the pull-out experiment show a noticeable dependence of the (out-of-plane) transverse mechanical response, which is primarily governed by the interlayer strength, on the stacking configurations. The degree of the dependence is directly related to the nature of the interlayer interactions, which change from covalent to covalent polar in going from graphene bilayer to graphene/BN to BN bilayer. In contrast, molecular dynamics simulations mimicking nanoindentation experiments predict that the in-plane mechanical response, which mainly depends on the intra-layer interactions, shows little or no dependence on the stacking-order. The BN monolayer is predicted to fracture before graphene regardless of the stacking pattern or configuration in the graphene/BN heterostructure, affirming the mechanical robustness of graphene. Thus, the graphene-based hybrid structures retain both stiffness and toughness required for a wide range of optoelectromechanical applications.

Anisotropic materials are of great interest due to their unique direction-dependent optical properties. Borophene, the two-dimensional analog of graphene consisting of boron atoms, has attracted immense research interest due to its exciting anisotropic electronic and mechanical properties. Its synthesis in several structural polymorphic configurations has recently been reported. The present work reports the layer-dependent optical absorption and hyperpolarizabilities of the buckled borophene (δ6-borophene). The results, based on density functional theory, show that multilayer borophene is nearly transparent with only a weak absorbance in the visible region, reflecting its anisotropic structural characteristics. The static first-order hyperpolarizability significantly increases with the number of layers, due mainly to interactions among the frontier orbitals in multilayer borophene. Transparency in the visible region combined with enhanced nonlinear optical properties makes the multilayer borophene important for future photonics technologies.