EFFECT OF HEXAGONALITY PERCENT ON THERMAL CONDUCTIVTY IN SILICON STRUCTURES.
Kessler, Samuel P
Kessler, Samuel P
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Abstract
Thermoelectric materials have the potential to be an extremely useful solid state power source and offer many benefits over traditional power sources; they have no moving parts, they are incredibly reliable, and most importantly clean. Their current limitation is poor energy conversion efficiency. Even the most efficient require very large temperature gradients just to provide small amounts of power, and do so at efficiencies less the 10%. However resent research developments have shown that nano-scale dimensions and interface boundaries have the potential to provide significant gains in efficiency by way of phonon scattering. This scattering has the effect of significantly reducing the thermal conductivity and in turn improving the thermoelectric figure of merit (ZT) in nano-scale materials such as silicon. This research explores the particular effect of extended regions of repeating twin boundary interfaces on the thermal conductivity of bulk silicon structures. Extended regions of twin boundaries are created by realizing that repeated twins have an identical cc’cc’cc’ stacking structure to the diamond-hexagonal stacking lattice structure of the silicon IV polytype, also known as 2H silicon. By modeling a 3C-2H silicon heterostructure different thicknesses of twin boundary regions were simulated using the molecular dynamics software LAMMPS (3C represents the diamond-cubic structure of the Si I polytype). These simulations calculated the thermo conductivities for the bulk 3C-2H silicon structure. It was expected that the thermal conductivities would develop a local minimum value as the 2H thickness increased, but results showed that varying the thickness of the twin boundary region had little effect on the thermal conductivity. Also undesired fluctuations in the temperature profiles across the bulk silicon structures ultimately resulted in a number of suggestions for creating an improved model.
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Date
2014-01-01