Seminar organised by CMT
 
Subject: Phonon Heat Transport in One-Dimensional Quantum-Dot Superlattices and Cross-Section Modulated Nanowires
Speaker: Prof. dr. V.M. Fomin, Institute for Integrative Nanosciences, IFW Dresden, Germany
 
Abstract:
 Theory of phonon heat transport is developed for Si-based acoustically mismatched one-dimensional (1D) quantum-dot superlattices [1] and cross-section modulated nanowires [2]. The phonon spectra are calculated in the framework of Face-centered cubic cell and Born – von Karman models of lattice dynamics. The phonon transport is analyzed using the Boltzmann transport equation.
In acoustically-mismatched Si-based 1D quantum-dot superlattices the phonon thermal conductivity can be suppressed by a factor of 5 to 30. The effect is explained by the removal of the high-energy and highvelocity  phonon modes from the heat flux due to their localization in quantum-dot superlattice segments and  the phonon scattering on the interfaces. For instance, in Si/Ge 1D quantum-dot superlattices a strong  reduction of the lattice thermal conductivity down to 0.5 W m^-1 K^-1 can be achieved depending on quantumdot  sizes and interface quality. These findings are in line with the recently measured values of the thermal conductivity in multilayered quantum-dot arrays [3].
Suppression of the thermal fluxes in the cross-section modulated nanowires as compared to the  homogeneous Si nanowire increases with temperature and reaches the values 1.5 to 5. Increase of the wide cross-section enhances the suppression of the thermal flux due to a rise in the number of the trapped highenergy  phonon modes, which do not carry heat in the cross-section modulated nanowires, and, correspondingly, to a drop in the phonon group velocities in cross-section modulated nanowires compared  with those of a homogeneous nanowire. The obtained results indicate that segmented and cross-section modulated nanowires are promising candidates for thermoelectric and thermoisolation applications.
References
1. D. L. Nika, E. P. Pokatilov, A. A. Balandin, V. M. Fomin, A. Rastelli, O. G. Schmidt, Physical Review B84, 165415 (2011).
2. D. L. Nika, A. I. Cocemasov, C. I. Isacova, A. A. Balandin, V. M. Fomin, O. G. Schmidt, Physical Review B, 85, 205439 (2012).
3. G. Pernot, M. Stoffel, I. Savic, F. Pezzoli, P. Chen, G. Savelli, A. Jacquot, J. Schumann, U. Denker, I. Monch, C. Deneke, O. G. Schmidt, J. M. Rampnoux, S. Wang, M. Plissonnier, A. Rastelli, S. Dilhaire, and N. Mingo, Nature Materials 9, 491 (2010).

When and where: Thursday, June 28, 2012 at 11.00 h in room U.024, Campus Groenenborger