The Fabrication of Thermoelectric Materials Using Functionalised Silicon Nanoparticles

Ashby, Shane (2015) The Fabrication of Thermoelectric Materials Using Functionalised Silicon Nanoparticles. Doctoral thesis, University of East Anglia.

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Silicon nanoparticles (SiNPs) can be synthesised by a variety of methods. A one-pot synthesis
based on the chemical reduction of inverse micelles has been used to produce SiNPs with ligands
of varying alkyl chain length. These particles were characterised to determine how the chain
length affects the surface functionalities and particle size. The particles produced show optical
properties typical of SiNPs produced by solution methods.
Silicon based materials are a potential alternative to current thermoelectric materials (e.g.
Bi2Te3) due to their abundance and low toxicity. Phenylacetylene functionalised SiNPs have been
synthesised using a bottom up approach. A cold pressed pellet of this material displays an
electrical conductivity of 18.1 S m-1, in addition to a high Seebeck coefficient and a low thermal
conductivity. These properties combine to give a figure of merit (ZT) of 0.6 at 300 K. This ZT value
is significant for a silicon based material, and comparable to that of other thermoelectric materials
such as Mg2Si, PbTe and Si-Ge alloy.
To investigate the effects that the doping of ligands have on the thermoelectric properties of
such materials, terthiophene functionalised SiNPs were synthesised and subsequently doped using
varying levels of NOBF4. The electrical resistivity shows a decrease of 7 orders of magnitude
between the undoped and optimised material although the electrical resistivity is still higher than
required for application. In addition, the material produced displays a modest ZT of 0.08.
Top down methods allow control of the carrier concentration of the silicon core, as the
material is doped prior to being broken down. Phenylacetylene SiNPs were synthesised using
electrochemical etching followed by functionalisation via a two-step chlorination-alkylation
process. These particles were characterised and their thermal stability analysed, showing a
maximum operation temperature of 200oC.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Users 2259 not found.
Date Deposited: 19 Jun 2015 10:48
Last Modified: 19 Jun 2015 10:48

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