Paper EN+AS+EM+SE-TuM13
The Effect of Particle Size and Surface Termination of n-Si on Thermal and Electrical Conductivity
Tuesday, November 11, 2014, 12:00 pm, Room 315
| Session: |
Fuel Formation and Thermal Transport |
| Presenter: |
Thomas Lopez, University of California - Riverside |
| Authors: |
T. Lopez, University of California - Riverside
L. Mangolini, University of California - Riverside
S. Bux, California Institute of Technology
J.P. Fleurial, California Institute of Technology
|
| Correspondent: |
Click to Email |
A discussion of synthesis and characterization of bulk nanocrystalline silicon with grain sizes of around 20 nm and thermal conductivities as small as 100 mW/cmK at room temperature, will be presented. Nanostructured materials have great potential for thermoelectric applications because of the reduction in thermal conductivity due to phonon scattering at grain boundaries [1] and silicon is a well-understood, cheap, earth-abundant material. Other silicon nanostructures, such as nanowires [2], are being investigated as viable thermoelectric materials. We have used, for the first time, the combination of a non-thermal plasma process for the synthesis of silicon nanocrystals with hot pressing to produce bulk nanostructured silicon samples. The non-thermal plasma synthetic route has been proposed for the production of photo-luminescent silicon quantum dots with narrow size distribution (3 +/- 0.5 nm) [3]. The same reactor has been scaled up to produce silicon nanocrystals at a rate of hundreds of milligrams per hour. Silicon powder with sizes between 5 nm and 15 nm has been produced using either silane (SiH4) or silicon tetrachloride (SiCl4), which are low-cost silicon precursors. Results have shown surface termination of the non-thermal plasma synthesized particle, i.e. H or Cl, play a role in densification kinetics. Hot pressing is a high pressure, high temperature process that allows for the production of samples with bulk like densities while limiting grain growth. In this study we have produced bulk (12 mm diameter, 2-4 mm in thickness) samples of nanocrystalline silicon with relative densities exceeding 95%. Characterization by XRD and TEM confirms that grain sizes are around 30 nm. The effects of surface termination of nano-silicon on grain growth and grain boundary conditions will be extensively discussed. 1. Dresselhaus, M.S., et al., Advanced Materials, 2007. 19(8): p. 1043-1053.
2. Hochbaum, A.I., et al., Nature, 2008. 451(7175): p. 163-U5.
3. Mangolini, L., et al., Nano Letters, 2005. 5(4): p. 655-659.