Enhancement of thermal transport properties of asymmetric Graphene/hBN nanoribbon heterojunctions by substrate engineering

Two-dimensional heterostructures offer a new route to manipulate phonons at the nanoscale. By performing non-equilibrium molecular dynamics simulations we address the thermal transport properties of structurally asymmetric graphene/hBN nanoribbon heterojunctions deposited on several substrates: graphite, Si(100), SiC(0001), and SiO2. Our results show a reduction of the interface thermal resistance in coplanar G/hBN heterojunctions upon substrate deposition which is mainly related to the increment on the power spectrum overlap. This effect is more pronounced for deposition on Si(100) and SiO2 substrates, independently of the planar stacking order of the materials. Moreover, it has been found that the thermal rectification factor increases as a function of the degree of structural asymmetry for hBN-G nanoribbons, reaching values up to similar to 24%, while it displays a minimum (is an element of[0.7, 2.4]) for G-hBN nanoribbons. More importantly, these properties can also be tuned by varying the substrate temperature, e.g., thermal rectification of symmetric hBN-G nanoribbon is enhanced from 8.8% to 79% by reducing the temperature of Si(100) substrate. Our investigation yields new insights into the physical mechanisms governing heat transport in G/hBN heterojunctions, and thus opens potential new routes to the design of phononic devices. (C) 2017 Elsevier Ltd. All rights reserved

Doping engineering of thermoelectric transport in BNC heteronanotubes

BNC heteronanotubes are promising materials for the design of nanoscale thermoelectric devices. In particular, the structural BN doping pattern can be exploited to control the electrical and thermal transport properties of BNC nanostructures. We here address the thermoelectric transport properties of (6,6)-BNC heteronanotubes with helical and horizontal BN doping patterns. For this, we use a density functional tight-binding method combined with the Green's function technique. Our results show that the electron transmission is reduced and the electronic bandgap increased as a function of the BN concentration for different doping distribution patterns, so that (6,6)-BNC heteronanotubes become semiconducting with a tunable bandgap. The thermal conductance of helical (6,6)-BNC heteronanotubes, which is dominated by phonons, is weakly dependent on BN concentration in the range of 30-80%. Also, the Seebeck coefficient is enhanced by increasing the concentration of helical BN strips. In particular, helical (6,6)-BNC heteronanotubes with a high BN concentration (>20%) display a larger figure of merit compared to other doping distributions and, for a concentration of 50%, reach values up to 2.3 times and 3.4 times the corresponding values of a CNT at 300 K and 800 K, respectively. Our study yields new insights into the parameters tuning the thermoelectric efficiency and thus provides a starting point for designing thermoelectric devices based on BNC nanostructures