| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Monday Sessions |
| Session TF+NM-MoE |
| Session: | Nanostructures, Graphene, and Magnetism |
| Presenter: | Yosuke Ayako, The University of Electro-Communications (UEC-Tokyo) and JST-CREST, Japan |
| Authors: | Y. Ayako, The University of Electro-Communications (UEC-Tokyo) and JST-CREST, Japan A. Akaishi, The University of Electro-Communications (UEC-Tokyo) and JST-CREST, Japan J. Nakamura, The University of Electro-Communications (UEC-Tokyo) and JST-CREST, Japan |
| Correspondent: | Click to Email |
Thermoelectric materials have attracted much attention because of their promising applications in power generation. Recently, we have shown that the superlattices consisting of zigzag graphene nanoribbons (GNRs) and BN nanoribbons (BNNRs) have giant Seebeck coefficients [1]. Such giant Seebeck coefficients of the superlattice models stem from the so-called pudding-mold band with a finite energy gap [2]. Although such types of superlattices have great fascination with thermoelectricity, the experimental synthesiss of these two-dimensional structures may be an extremely-challenging task.
In the present study, we suggest more easy-to-make, practical one-dimensional structures possessing the pudding-mold band. We propose the graphene/h-BN hybrid nanoribbons with zigzag edges (hereafter referred to as “nano-composites”), in which both edges of GNRs are terminated with BNNRs. In this study, we specify the models using integer n and m, which are the numbers of dimer lines of GNRs and BNNRs, respectively. The Seebeck coefficients of nano-composites have been evaluated on the basis of the Bolzmann transport theory. Electronic band structures have been calculated using the first-principles calculations within the framework of the density functional theory. We have also employed the armchair nano-composites for comparison.
We have shown that the pudding-mold bands have been confirmed for the zigzag nano-composites, but not for the armchair ones. The Seebeck coefficients for the zigzag nano-composites decrease monotonically with increasing n. Their maximum values become higher than those for graphene and GNRs, though not to the extent of the superlattices [1]. On the other hand, the Seebeck coefficients for the armchair nano-composites do not become higher compared with those for the pristine armchair GNRs, since the mechanism of the enhancement based on the pudding-mold band does not work for these composites. Here, we should not overlook that the Seebeck coefficients for the armchair nano-composites show the oscillatory-decreasing behavior with increasing n, and their dependence on n can be classified into three categories of 3n, 3n+1, and 3n+2, being analogous to the electronic structure of the zigzag carbon nanotubes [3]. Nevertheless, the Seebeck coefficients shows the universal dependence on the band gaps: the maximal, absolute Seebeck coefficient depends only on the bandgap irrespective of the structural category of nano-composites.
[1]Y. Yokomizo and J.Nakamura, Appl. Phys. Lett. 103, 113901 (2013).
[2]K. Kuroki et al., J. Phys. Soc. Jpn. 76, 083707 (2007).
[3]R. Saito et al., Physcal Properties of Carbon Nanotubes (Imperial College Press, 1998).