Abstract: X-ray diffraction studies comparing the transformation of C(60) and C(70) peapods into double walled carbon nanotubes are presented. The structures of the as-formed DWCNTs are strikingly similar, showing that they are not dependent on the nature of the fullerene precursor. High temperature X-ray diffraction measurements of C(70) peapods below the coalescence temperature show that confined C(70) molecules in large tubes undergo an orientational. transition to free rotations. Fast re-orientations of C(70) molecules allow cyclo-addition between adjacent fullerenes to form, in good agreement with the mechanism of coalescence proposed in the literature for C(60) molecules. (C) 2009 Elsevier Ltd. All rights reserved.

Abstract: Two-dimensional (2D) carbon nitride materials play an important role in energy-harvesting, energy-storage and environmental applications. Recently, a new carbon nitride, 2D polyaniline (C3N) was proposed [PNAS 113 (2016) 7414-7419]. Based on the structure model of this C3N monolayer, we propose two new carbon nitride monolayers, named dumbbell (DB) C4N-I and C4N-II. Using first-principles calculations, we systematically study the structure, stability, and band structure of these two materials. In contrast to other carbon nitride monolayers, the orbital hybridization of the C/N atoms in the DB C4N monolayers is sp(3). Remarkably, the band structures of the two DB C4N monolayers have a Dirac cone at the K point and their Fermi velocities (2.6/2.4 x 10(5) m/s) are comparable to that of graphene. This makes them promising materials for applications in high-speed electronic devices. Using a tight-binding model, we explain the origin of the Dirac cone. (C) 2017 Elsevier Ltd. All rights reserved.

Abstract: Using the first-principles calculations, we explore the structural and novel electronic/optical properties of the C2N nanosheet. To this goal, we systematically investigate the affect of layer thickness, electrical field and strain on the electronic properties of the C2N nanosheet. By increasing the thickness of C2N, we observed that the band gap decreases. Moreover, by applying an electrical field to bilayer C2N, the band gap decreases and a semiconductor-to-metal transition can occur. Our results also confirm that uniaxial and biaxial strain can effectively alter the band gap of C2N monolayer. Furthermore, we show that the electronic and magnetic properties of C2N can be modified by the adsorption and substitution of various atoms. Depending on the species of embedded atoms, they may induce semiconductor (O, C, Si and Be), metal (S, N, P, Na, K, Mg and Ca), dilute-magnetic semiconductor (H, F, B), or ferro-magnetic-metal (Cl, Li) character in C2N monolayer. It was also found that the inclusion of hydrogen or oxygen impurities and nitrogen vacancies, can induce magnetism in the C2N monolayer. These extensive calculations can be useful to guide future studies to modify the electronic/optical properties of two-dimensional materials. (C) 2019 Elsevier Ltd. All rights reserved.

Abstract: Using evolutionary algorithm for crystal structure prediction, we present a new stable two-dimensional (2D) carbon allotrope composed of polymerized as-indacenes (PAI) in a zigzag pattern, namely PAI-graphene whose energy is lower than most of the reported 2D allotropes of graphene. Crucially, the crystal structure realizes a nonsymmorphic layer group that enforces a nontrivial global topology of the band structure with two Dirac cones lying perfectly at the Fermi level. The absence of electron/hole pockets makes PAI-graphene a pristine crystalline topological semimetal having anisotropic Fermi velocities with a high value of 7.0 x 10(5) m/s. We show that while the semimetallic property of the allotrope is robust against the application of strain, the positions of the Dirac cone and the Fermi velocities can be modified significantly with strain. Moreover, by combining strain along both the x- and y-directions, two band inversions take place at G leading to the annihilation of the Dirac nodes demonstrating the possibility of strain-controlled conversion of a topological semimetal into a semiconductor. Finally we formulate the bulk-boundary correspondence of the topological nodal phase in the form of a generalized Zak-phase argument finding a perfect agreement with the topological edge states computed for different edge-terminations. (C) 2020 The Author(s). Published by Elsevier Ltd.

Abstract: Hyperbolic polaritons in ultra thin materials such as few layers of van derWaals heterostructures provide a unique control over light-matter interaction at the nanoscale and with various applications in flat optics. Natural hyperbolic surface plasmons have been observed on thin films of WTe2 in the light wavelength range of 16-23 mu m (similar or equal to 13-18 THz) [Nat. Commun. 11, 1158 (2020)]. Using time-dependent density functional theory, it is found that carbon doped monolayer phosphorene (beta-allotrope of carbon phosphide monolayer) exhibits natural hyperbolic plasmons at frequencies above similar or equal to 5 THz which is not observed in its parent materials, i.e. monolayer of black phosphorous and graphene. Furthermore, we found that by electrostatic doping the plasmonic frequency range can be extended to the mid-infrared. (C) 2021 Elsevier Ltd. All rights reserved.

Abstract: Methods used to strengthen metals generally also cause a pronounced decrease in ductility and electrical conductivity. In this work a bioinspired strategy is applied to surmount the dilemma. By assembling copper submicron flakes cladded with in-situ grown graphene, graphene/copper matrix composites with a nanolaminated architecture inspired by a natural nacre have been prepared. Owing to a combined effect-from the bioinspired nanolaminated architecture and improved interfacial bonding, a synergy has been achieved between mechanical strength and ductility as well as electrical conductivity in the graphene/copper matrix composites. With a low volume fraction of only 2.5% of graphene, the composite shows a yield strength and elastic modulus similar to 177% and similar to 25% higher than that of unreinforced copper matrix, respectively, while retains ductility and electrical conductivity comparable to that of pure copper. The bioinspired nanolaminated architecture enhances the efficiencies of two-dimensional (2D) graphene in mechanical strengthening and electrical conducting by aligning graphene to maximize performance for required loading and carrier transporting conditions, and toughens the composites by crack deflection. Meanwhile, in-situ growth of graphene is beneficial for improving interfacial bonding and structural quality of graphene. The strategy sheds light on the development of composites with good combined structural and functional properties. (C) 2017 Elsevier Ltd. All rights reserved.