Entanglement and the nonlinear elastic behavior of forests of coiled carbon nanotubes

Helical or coiled nanostructures have been object of intense experimental and theoretical studies due to their special electronic and mechanical properties. Recently, it was experimentally reported that the dynamical response of foamlike forest of coiled carbon nanotubes under mechanical impact exhibits a nonlinear, non-Hertzian behavior, with no trace of plastic deformation. The physical origin of this unusual behavior is not yet fully understood. In this work, based on analytical models, we show that the entanglement among neighboring coils in the superior part of the forest surface must be taken into account for a full description of the strongly nonlinear behavior of the impact response of a drop-ball onto a forest of coiled carbon nanotubes.Comment: 4 pages, 3 figure

Mechanical properties of Graphene Nanoribbons

Herein, we investigate the structural, electronic and mechanical properties of zigzag graphene nanoribbons upon the presence of stress applying Density Functional Theory within the GGA-PBE approximation. The uniaxial stress is applied along the periodic direction, allowing a unitary deformation in the range of +/- 0.02%. The mechanical properties show a linear-response within that range while the non-linear dependence is found for higher strain. The most relevant results indicate that Young's modulus is considerable higher than those determined for graphene and carbon nanotubes. The geometrical reconstruction of the C-C bonds at the edges hardness the nanostructure. Electronic structure features are not sensitive to strain in this linear elastic regime, being an additional promise for the using of carbon nanostructures in nano-electronic devices in the near future.Comment: 30 pages. J. Phys.: Condens. Matter (accepted

Molecular Dynamics Simulations of Carbon Nanotubes as Gigahertz Oscillators

Recently Zheng and Jiang [PRL 88, 045503 (2002)], based on static models, have proposed that multiwalled carbon nanotubes could be the basis for a new generation of nanooscilators in the several gigahertz range. In this work we present the first molecular dynamics simulation for these systems. Different nanotube types were considered in order to verify the reliability of such devices as gigahertz oscillators. Our results show that these nanooscillators are dynamically stables when the radii difference values between inner and outer tubes are of ~ 3.4 A. Frequencies as large as 38 GHz were observed, and the calculated force values are in good agreement with recent experimental investigations. Moreover, our results contradict some predictions made by Zheng and Jiang.Comment: 4 pages, 6 figure

Magnetic Properties of Single Transition-Metal Atom Absorbed Graphdiyne and Graphyne Sheet

The electronic and magnetic properties of single 3d transition-metal(TM) atom (V, Cr, Mn, Fe, Co, and Ni) adsorbed graphdiyne (GDY) and graphyne (GY) are systematically studied using first-principles calculations within the density functional framework. We find that the adsorption of TM atom not only efficiently modulates the electronic structures of GDY/GY system, but also introduces excellent magnetic properties, such as half-metal and spin-select half-semiconductor. Such modulation originates from the charge transfer between TM adatom and the GDY/GY sheet as well as the electron redistribution of the TM intra-atomic s, p, and d orbitals. Our results indicate that the TM adsorbed GDY/GY are excellent candidates for spintronics.Comment: 8 pages, 7 figure

Initial stages of graphene oxide cracking in basic media

Despite the increasing interest in graphene oxide (GO) and its properties, currently there is no consensus on its structure. In the recently proposed two-component model, the GO structure consists of slightly oxidized graphene sheets and small organic molecules physisorbed on them. The formation of these molecules has been later attributed to the GO rupture caused by basic treatment under heating. In this work, we studied the initial stages of the GO rupture in hydroxyl chains by using first principles electronic calculations. Possible routes to cracking originated from different configurations of hydroxyl chains and under possible reactions in basic media were analyzed. Resulting from successive hydroxide ion attacks, cracks were observed for chains with hydroxyls arranged in armchair and zigzag configurations. Bond breaking due to the presence of ketones located at opposite sides of the basal plane was shown to play a role on cracking initiation and propagation. Cracking driven by structural deformations was also observed for chains comprised of parallelly orientated vicinal diols142217223FAPESB – Fundação de Amparo á Pesquisa Do Estado Da Bahia2010/50646-6; 2016/01736-