Impact of vacancies on the thermal conductivity of graphene nanoribbons: A molecular dynamics simulation study

Equilibrium molecular dynamics simulation using 2nd generation Reactive Bond Order interatomic potential has been performed to model the thermal transport of nanometer sized zigzag defected graphene nanoribbons (GNRs) containing several types of vacancies. We have investigated the thermal conductivity of defected GNRs as a function of vacancy concentration within a range of 0.5% to 5% and temperature ranging from 300K to 600K, along with a comparative analysis of those for pristine GNRs. We find that, a vacancy concentration of 0.5% leads to over 90% reduction in the thermal conductivity of GNRs. At low defect concentration, the decay rate is faster but ceases gradually at higher defect concentration. With the increasing temperature, thermal conductivity of defected GNRs decreases but shows less variation in comparison with that of pristine GNRs at higher temperatures. Such comprehensive study on several vacancy type defects in GNRs can provide further insight to tune up the thermal transport characteristics of low dimensional carbon nanostructures. This eventually would encourage the characterization of more stable thermal properties in thermal devices at an elevated temperature as well as the potential applicability of GNRs as thermoelectrics

Equilibrium Molecular Dynamics (MD) Simulation Study of Thermal Conductivity of Graphene Nanoribbon: A Comparative Study on MD Potentials

The thermal conductivity of graphene nanoribbons (GNRs) has been investigated using equilibrium molecular dynamics (EMD) simulation based on Green-Kubo (GK) method to compare two interatomic potentials namely optimized Tersoff and 2nd generation Reactive Empirical Bond Order (REBO). Our comparative study includes the estimation of thermal conductivity as a function of temperature, length and width of GNR for both the potentials. The thermal conductivity of graphene nanoribbon decreases with the increase of temperature. Quantum correction has been introduced for thermal conductivity as a function of temperature to include quantum effect below Debye temperature. Our results show that for temperatures up to Debye temperature, thermal conductivity increases, attains its peak and then falls off monotonically. Thermal conductivity is found to decrease with the increasing length for optimized Tersoff potential. However, thermal conductivity has been reported to increase with length using 2nd generation REBO potential for the GNRs of same size. Thermal conductivity, for the specified range of width, demonstrates an increasing trend with the increase of width for both the concerned potentials. In comparison with 2nd generation REBO potential, optimized Tersoff potential demonstrates a better modeling of thermal conductivity as well as provides a more appropriate description of phonon thermal transport in graphene nanoribbon. Such comparative study would provide a good insight for the optimization of the thermal conductivity of graphene nanoribbons under diverse conditions

ZIM cover for improvement of the bandwidth and gain of patch antenna

A new zero-index metasurface (ZIM) structure is proposed to improve the bandwidth and gain of the microstrip patch antenna. A single-sided 8 × 8 set of metasurface elements is embedded over the radiating patch to enhance the performance of a coaxial probe fed slotted circular patch antenna. The proposed ZIM cover-assimilated antenna were designed on a high permittivity (ϵr = 15) ceramic-filled bio-plastic sandwich structured dielectric substrate and fabricated for experimental verification of the performance characteristics. A significant improvement of bandwidths and gains of the proposed antenna were observed by incorporating the metasurface cover over the radiating patch with the gap of 10 mm. The experimental results showed that the bandwidths of the proposed metasurface-covered antenna widened by 54.5%, 68.5% and 61.1% and gains also improved by 133.40%, 73.30% and 72.06% at three resonant frequencies, namely, 3.7 GHz, 8.95 GHz and 10.3 GHz, respectively, compared to the patch alone. The performance characteristics of the proposed ZIM cover-incorporated antenna make it suitable for ultra-wideband (3.4-4 GHz, 6.45-8.2 GHz and 10.0-10.9 GHz) applications