The role of atomic vacancies and boundary conditions on the ballistic thermal transport in graphene nanoribbons

P. SCURACCHIO; S. COSTAMAGNA; F. M. PEETERS; A. DOBRY

Zurich

Workshop; CECAM Workshop on graphene's strain engineering: Establishing connections between Condensed Matter Physics, Relativistic Quantum Field Theory, and Computational Mechanics; 2014

CECAM - Centro Europeo de Calculo atomico y molecular

We study theoretically the quantum thermal transport in graphene nanoribbons under the presence of single atomic vacancies and subjected to different edge conditions. We start with a full comparison of the phonon polarizations and energy dispersions, at low energy, as given by a fifth nearest neighbor force constant model (5FNNCM) [1] and the elasticity theory of continuum membranes [2,3]. In particular, we discuss the behavior of an additional acoustic edge-localized flexural mode, named fourth acoustic branch (4ZA), which appears at finite energy through the 5FNNCM for both, armchair (ARM) and zig-zag (ZZ) ribbons. Then, by means of the non equilibrium Green's function technique (NEGF) we obtain results for the ballistic thermal conductance and identify the contribution of every single phonon mode at low energy for the case of ZZ ribbons [4]. The main results are the following. While edge and central located single atomic vacancies do not affect the transmission function of in-plane phonon modes, they reduce considerably contributions from flexural modes. We found that boundary conditions have also strong impact on the thermal transport properties. Different to what occurs in free-standing, clamped ribbons have a sample size dependent energy gap in the phonon spectrum. This energy gap is particularly large for in-plane phonon modes which implies that at low temperatures the thermal transport is dominated only by flexural phonon modes. These findings could open a route to design graphene based devices where it is possible discriminate the relative contribution of polarized phonons and govern thus the thermal transport on the nanoscale [5]. References [1] K. H. Michel and B. Verberck. Phys. Rev B 78, 085424 (2008). [2] P. Scuracchio and A. Dobry. Phys. Rev. B 87, 165411 (2013). [3] S. Costamagna and A. Dobry. Phys. Rev. B 83, 233401 (2011). [4] Z. Huang, T. S. Fisher, and J. Y. Murthy. Journal of Applied Physics 108, 094319 (2010). [5] E. Pop, V. Varshney, and A. K. Roy. MRS Bulletin, Vol. 37 (2012).