Newsletter 107 - October 2011 - (pdf - 0.6 MB) - Psi-k

Thermal conductivity of Si nanostructures containing defects:
Methodology, isotope effects, and phonon trapping
T. M. Gibbons 1 , By. Kang 1 , and S. K. Estreicher 1 , and Ch. Carbogno 2
1 Texas Tech University, Lubbock, Texas 79409-1051, USA
2 Fritz-Haber-Institut der Max-Planck-Gesellschaft,
Faradayweg 4–6, 14195 Berlin, Germany
Abstract
A first-principles method to calculate the thermal conductivity in nanostructures that
may contain defects or impurities is described in detail. The method mimics the so-called
laser-flash technique to measure thermal conductivities. It starts with first-principles densityfunctional
theory and involves the preparation of various regions of a supercell at slightly
different temperatures. The temperature fluctuations are minimized without using a thermostat
and, after averaging over random initial conditions, temperature changes as small as
5 K can be monitored (from 120 to 125 K). The changes to the phonon density of states and
the specific heat induced by several atomic percent of impurities are discussed. The thermal
conductivity of Si supercells is calculated as a function of the temperature and of the
impurity content. For most impurities, the drop in thermal conductivity is unremarkable.
However, there exist narrow ranges of impurity parameters (mass, bond strength, etc.) for
which substantial drops in the thermal conductivity are predicted. These drops are isotope
dependent and appear to be related to the vibrational lifetime of specific impurity-related
modes.
(Phys. Rev. B 84, 035317 (2011))
Contact person: Christian Carbogno (carbogno@fhi-berlin.mpg.de)
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