ICT2014 Abstracts

Engineering heat conduction through nanoscale devices via manipulation of phonons is of practical interest,  especially for designing highly efficient thermoelectric devices. In particular, nanoscale devices can be engineered such that the phonon transport is blocked/reduced while the electron transport is less interrupted, which results in higher thermoelectric conversion efficiency. However, the fundamental atomicity of the underlying material and the complex nature of the phonon modes demand a full quantum mechanical treatment of thermal transport in these nanoscale systems.

In this work, using first principles Density Functional Theory (DFT) calculations coupled with the Green’s function approach and the Landauer formalism, we have studied the coherent electron/phonon conductance and the thermoelectric properties of [111]-oriented Si/Ge core-shell nanowires having diameters from 0.55 nm to 1.36 nm. In these structures, the DFT-based study of coherent nature of phonon conductance becomes important when the fundamental atomicity of the underlying lattice cannot be ignored, a fact that has recently been verified experimentally [1]. Our detailed analysis of phonon modes shows that thermal conductance due to selective phonon modes of Si/Ge core/shell nanowires can be suppressed by engineering the ratio of core/shell atoms (that is, chemical composition of the structure), while keeping the electron transport less interrupted. Furthermore, our current efforts and results on studying the effects of phonon-phonon scattering on the thermal conductance (by solving the Boltzmann transport equation using a Monte Carlo approach enabled by the DFT derived microscopic bandstructure parameters)  will be presented at the conference.

[1] M. N. Luckyanova et al., “Coherent phonon heat conduction in superlattices”, Science, 338, 936, (2012).