The Fabrication of Thermoelectric Materials Using Functionalised Silicon Nanoparticles

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.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2015

Author dc:creator

• Ashby, Shane

Language dc:language

en