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We report ab initio calculations of spin-dependent transport in single atomic carbon chains bridging two zigzag graphene nanoribbon electrodes. Our calculations show that carbon atomic chains coupled to graphene electrodes are perfect spin-filters with almost 100 % spin polarization. Moreover, carbon atomic chains can also show a very large bias-dependent magnetoresistance up to 10 6 % as perfect spin-valves. These two spin-related properties are independent on the length of carbon chains. Our report, the spin-filter and spin-valve are conserved in a single device simultaneously, opens a new way to the application of all-carbon composite spintronics.Due to the ballistic quantum transport and remarkable long spin-coherence times and distances in carbon-based nanostructures, all-carbon nanodevices have attracted considerable attention for their possible application in electronics or spintronics.1,2 Recently, all-carbon graphene nanoribbon (GNR) based field-effect transistors (FETs) are experimentally fabricated by Ponomarenko et al., which make all-carbon electronics devices becoming realization.3 In order to get semiconducting GNRFETs, sub-10-nm GNRs is necessary but difficult to get due to the limitation of the current lithography technique.4 Very recently, linear carbon atomic chains have been carved out from graphene with a high energy electron beam in two groups.5,6 Such ground-breaking experiments pave a wave for novel allcarbon FETs with many merits compared with GNR-or carbon nanotube-(CNT) based one. The reason is that carbon atomic chains are identical and can be considered as extremely narrow GNRs or thin CNTs. Therefore, they eliminate the need for sorting through a pile of different chiral GNRs and CNTs. Motivated by experiments, Shen et al:and Chen et al: theoretically studied the electron transport properties of carbon chain-graphene junctions and discussed their potential applications in electronics.7,8Spintronics is an emerging technology that exploits the intrinsic spin degree of freedom of the electron. Several carbon-based materials are proposed for spintronics applications, such as graphene and carbon nanotubes. Graphene can be used as a spin valleytronics device by adjusting of its band valley9 and Zigzag edged GNRs are predicted to be half-metallic under electrical field, which can be used as a spintronics device.10 Tombros et al: experimentally studied spin-diffusion in graphene device and observed long spin flip time/length.11 Kim et al: theoretically predicted a very large values of magnetoresistance in a GNR-based all-carbon FET as a spin valve.12-14 Karpan et al: predicted graphene as a perfect spin filter when bridging ferromagnetic leads.15 The narrowest GNRs, carbon atomic chains, also have been theoretically studied as perfect spin filters between nonmagnetic Au electrodes or spin-valves bridging Al electrodes under magnetic fields.16,17 Moreover, modified carbon chains have been predicted as spin-filters or spin-valves. For example, Yang et al: proposed half-metallic properties of c...

Silicene is a monolayer of silicon atoms arranged in honeycomb lattice similar to graphene. We study the thermal transport in silicene by using non-equilibrium molecular dynamics simulations. We focus on the effects of tensile strain and isotopic doping on the thermal conductivity, in order to tune the thermal conductivity of silicene. We find that the thermal conductivity of silicene, which is shown to be only about 20% of that of bulk silicon, increases at small tensile strains but decreases at large strains. We also find that isotopic doping of silicene results in a U-shaped change of the thermal conductivity for the isotope concentration varying from 0% to 100%. We further show that ordered doping (isotope superlattice) leads to a much larger reduction in thermal conductivity than random doping. Our findings are important for the thermal management in silicene-based electronic devices and for thermoelectric applications of silicene.

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We investigated effects of hydrogen passivation of edges of armchair graphene nanoribbons (AGNRs) on their electronic properties using first-principles method. The calculated band gaps of the AGNRs vary continually over a range of 1.6 eV as a function of a percentage of sp3-like bonds at the edges. This provides a simple way for band gap engineering of graphene as the relative stability of sp2 and sp3-like bonds at the edges of the AGNRs depends on the chemical potential of hydrogen gas, and the composition of the sp2 and sp3-like bonds at the edges of the AGNRs can be easily controlled experimentally via temperature and pressure of H2 gas.

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Understanding the grain size-dependent failure behavior of polycrystalline graphene is important for its applications both structurally and functionally. Here we perform molecular dynamics simulations to study the failure behavior of polycrystalline graphene by varying both grain size and distribution. We show that polycrystalline graphene fails in a brittle mode and grain boundary junctions serve as the crack nucleation sites. We also show that its breaking strength and average grain size follow an inverse pseudo Hall-Petch relation, in agreement with experimental measurements. Further, we find that this inverse pseudo Hall-Petch relation can be naturally rationalized by the weakest-link model, which describes the failure behavior of brittle materials. Our present work reveals insights into controlling the mechanical properties of polycrystalline graphene and provides guidelines for the applications of polycrystalline graphene in flexible electronics and nano-electronic-mechanical devices.