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A5: Nanoscale and low dimensional effects

Effects of particle size on the thermal diffusivity of SPS pressed silicon powders.

Shane P. Ashby1, Yimin Chao1, Huanpo Ning2 and Michael J. Reece2
1. Energy Materials Laboratory, School of Chemistry, University of East Anglia, UK2. Nanoforce Technology Ltd., Queen Mary, University of London UK

The production of nanostructured bulk materials from silicon powders has been described as being on way of bringing down the thermal conductivity of silicon while still maintaining its high power factor. This reduction of thermal conductivity is predicted to lead to significant increases in ZT[1].

The starting size of the particles has a major effect on the nanostructuring of silicon based materials. Using particles of differing size and distribution we have investigated the effects this has had on the temperature dependant thermal diffusivity of a pellet pressed using spark plasma sintering (SPS).

Results show a significant lowering in the thermal diffusivity as the particle size in the powders is decreased. As the particle size deceases from 1um to 60 nm we see a 10 fold decrease in the thermal conductivity at 300 K from 20 mm2S-1 to 2 mm2S-1 of a pellet of comparable density. Both of these show a significant a decrease from the thermal diffusivity of 90 mm2S-1 observed bulk silicon[2]. Further decreases would be expected when the particle size is decrease from 60 nm to the sub 10 nm particle size observed in silicon quantum dots.

[1]Bux, S. K.; Blair, R. G.; Gogna, P. K.; Lee, H.; Chen, G.; Dresselhaus, M. S.; Kaner, R. B.; Fleurial, Adv. Funct. Mater. 2009, 19, 2445-2452.

[2] Shanks, H. R., P. D. Maycock, P. H. Sidles, and G. C. Danielson, Phys. Rev. 1963, 130, 1743-1748.