New insights into NO adsorption on alkali metal and transition metal doped graphene nanoribbon surface: A DFT approach.

The aim of this article is to investigate the sensing performance of NO gas molecule on the graphene nanoribbon domain for the determination of structural and electronic properties. Effect of an alkali metal (lithium) and a transition metal (iron) on the armchair oriented graphene nanoribbon (ArGNR) surface for the sensing purpose of NO gas has been performed through the quantum mechanics based Density Functional Theory (DFT) calculations. Various configurations of ArGNR doped with Li and Fe atoms such as one-edge doped, center doped, both-edge doped Li-ArGNR and Fe-ArGNR have been simulated, and a detailed comparative study of lithium and iron doping on different configurations of ArGNRs for the adsorption energy, stability analysis, band gap analysis and density of states analysis has been quantitatively evaluated. By comparing the adsorption energy of NO, it is found that Li doping enhances the strength of NO adsorption on the different variants of ArGNR. Computational results predict that the undoped ArGNR is insensitive to the NO gas adsorption with adsorption energy of about -0.41 eV. Our results determine that substitutional doping of Li doping at one edge doped and both-edge doped position increases the adsorption abilities of ArGNRs in these configurations with adsorption energies of approximately -6.92 eV and -9.64 eV that is 16 and 23 times greater than the pristine ArGNR (Pr-ArGNR). Band nature for both type of doping estimates the changing behavior of ArGNRs from semiconductor to metallic transition after the adsorption of NO molecule. It is concluded that the Li doping at one edge and both edge position of ArGNR makes it an excellent potential sensing material for the sensing purpose of NO gas as compared to the Fe doped configurations.

ReaxFF reactive molecular dynamics simulations to study the interfacial dynamics between defective h-BN nanosheets and water nanodroplets.

In this work, the authors have developed a reactive force field (ReaxFF) to investigate the effect of water molecules on the interfacial interactions with vacancy defective hexagonal boron nitride (h-BN) nanosheets by introducing parameters suitable for the B/N/O/H chemistry. Initially, molecular dynamics simulations were performed to validate the structural stability and hydrophobic nature of h-BN nanosheets. The water molecule dissociation mechanism in the vicinity of vacancy defective h-BN nanosheets was investigated, and it was shown that the terminal nitrogen and boron atoms bond with a hydrogen atom and hydroxyl group, respectively. Furthermore, it is predicted that the water molecules arrange themselves in layers when compressed in between two h-BN nanosheets, and the h-BN nanosheet fracture nucleates from the vacancy defect site. Simulations at elevated temperatures were carried out to explore the water molecule trajectory near the functionalized h-BN pores, and it was observed that the intermolecular hydrogen bonds lead to agglomeration of water molecules near these pores when the temperature was lowered to room temperature. The study was extended to observe the effect of pore sizes and temperatures on the contact angle made by a water nanodroplet on h-BN nanosheets, and it was concluded that the contact angle would be less at higher temperatures and larger pore sizes. This study provides important information for the use of h-BN nanosheets in nanodevices for water desalination and underwater applications, as these h-BN nanosheets possess the desired adsorption capability and structural stability.

Enhanced thermal transport across a bi-crystalline graphene-polymer interface: an atomistic approach.

The objective of this investigation was to elaborate on the influence of grain boundaries on the interfacial thermal conductance between bi-crystalline graphene and polyethylene in a nanocomposite. Reverse non-equilibrium molecular dynamics simulations were implemented in combination with Lennard-Jones and reactive force field interatomic potential parameters. According to the simulation results, high-energy grain boundary atoms in bi-crystalline graphene played a substantial role in enhancing the interfacial thermal conductance values. To further illuminate the mechanisms of enhanced graphene-polyethylene interfacial thermal conductance in the presence of grain boundaries, a systematic study on the vibrational density of states and structural evolution was also performed. It was found that the vibrational coupling between bi-crystalline graphene and the polymer was enhanced; whereas a decline in the radial density profile and coordination number resulted in a shifting of the in-plane vibrational modes such that they amalgamated with those of the polyethylene matrix. Thus, bi-crystalline graphene can be considered to be a superior potential reinforcement for nanocomposites as compared to the pristine configuration for applications in thermoelectric and thermal interface materials.

Molecular dynamics based simulations to study the fracture strength of monolayer graphene oxide.

The aim of this article is to study the effects of functional groups such as hydroxyl, epoxide and carboxyl on the fracture toughness of graphene. These functional groups form the backbone of the intrinsic atomic structure of graphene oxide (GO). Molecular dynamics based simulations were performed in conjunction with reactive force field parameters to capture the Mode-I fracture toughness of functionalised graphene. Simulations were performed in stages, to study the effect of these functional groups, individually as well as all together on the fracture toughness of GO nanosheets. The molecular dynamics based simulations performed in this article helps us to conclude that the spatial distribution and concentration of functional groups significantly affects the fracture behavior of GO nanosheets.

The effect of STW defects on the mechanical properties and fracture toughness of pristine and hydrogenated graphene.

Graphene is emerging as a versatile material with a diverse field of applications. Synthesis techniques for graphene introduce several topological defects such as vacancies, dislocations and Stone-Thrower-Wales (STW) defects. Among them STW defects are generated without deleting any atom from the lattice position, but are introduced by rotating single C-C bonds. In this article, molecular dynamics based simulations have been performed to study the effect of STW defects on the fracture toughness of pristine graphene as well as graphene with crack edges passivated with hydrogen atoms. STW defects help in generating out of plane displacement in conjunction with redistribution of stress around the crack edges that can be used to improve the fracture toughness of brittle graphene. An overall improvement in the fracture toughness of pristine graphene as well as graphene containing hydrogen at the crack edges was predicted in this work.