Thermal transport in multilayer silicon carbide nanoribbons: reverse non-equilibrium molecular dynamics.

The heat conduction performance of materials has a crucial role in deciding their functional efficiency. For this purpose, the present study explores the structural and thermal properties of multilayer silicon carbide nanoribbons (SiCNRs). At first, we realize that the smallest values of cohesive energy correspond to the system with the largest interlayer distance due to vdW forces. The effects of stacking layers, their number, edge chirality, ribbon width, temperature (T) as well as coupling strength between the layers on the thermal conductivity, are all examined and discussed, using reverse nonequilibrium molecular dynamics. This results in an anisotropic trend of κ in terms of some parameters due to phonon scattering. By analyzing the various phonon properties, including phonon density of states, phonon dispersion relations as well as phonon mean free path, we gain critical insights into the mechanism of heat conduction in the systems. System size results reveal that thermal conductivities follow an increasing behavior with length and a decreasing trend with width as well as temperature, which is attributed to the phonon-phonon scattering rate. Furthermore, the thermal conductivities drift from the normal 1/T law and show an anomalous decreasing behavior above room temperature. Overall, these results offer a deep understating towards the thermal conductivity of n-SiCNRs and could promote their potential applications in thermoelectric and nanoelectronic devices.

Graphene-based SiC Van der Waals heterostructures: nonequilibrium molecular dynamics simulation study.

The structural properties and thermal conductivity of graphene-based SiC heterostructures are investigated using the reverse nonequilibrium molecular dynamics. The C/SiC/C heterostructure has the greatest value of cohesive energy due to the effect of vdW interactions between layers. The surfaces of heterostructures begin to ripple as a direct consequence of the plane fluctuations observed around T = 400 K. The thermal conductivity at room temperature is determined. The length and the armchair and zigzag orientations increase the magnitude of κ which decreases with increasing temperature. This change is attributed to the phonon Umklapp scattering and phonon cross-plane couplings. The impact of point vacancy, bi-vacancy and edge vacancy in a concentration range up to 2% is also discussed. The localization of low-frequency phonons around the vacancy induces a decaying characteristic of thermal conductivity. The effect depends on the type of vacancy and is more pronounced in heterostructures with point vacancy. The present results make pristine and defective heterostructures promising materials for various thermoelectric applications with tunable functionalities.

A signature index for third order topological insulators.

In this work, we develop an index signature characterising the third order topological phases in 3D systems. This index is an alternating sum of monomial signatures of Higgs triplet values at 3D corners. We extend our method to N-dimensional systems with open boundaries, and demonstrate that the topological invariant can be efficiently generalised to any space dimension including the second order topological insulators. Known results on lower dimensional systems are recovered and an interpretation in the Higgs space parameters is given.

DFT investigations of the hydrogenation effect on silicene/graphene hybrids.

We report here a study on the effect of hydrogenation on a new one-atom thick material made of silicon and carbon atoms (silicene/graphene (SG) hybrid) within density functional theory. The structural, electronic and magnetic properties are investigated for non-, semi- and fully hydrogenated SG hybrids in a chair configuration and are compared with their parent materials. Calculations reveal that pure SG is a non-zero band gap semi-conductor with stable planar honeycomb structure. So mixing C and Si in an alternating manner gives another way to generate a finite band gap in one-atom thick materials. Fully hydrogenation makes the gap larger; however half chemical modification with H reduces the gap in favor of ferromagnetism order. The findings of this work open a wide spectrum of possibilities for designing SG-based nanodevices with controlled and tuned properties.