Thermoelectric efficiency breakthrough in Si nanowires

C&I Issue 2, 2008

Heat energy that is currently wasted could one day be harnessed by engineering silicon at the nanoscale, turning people into walking batteries and making power stations much more efficient.

Two US teams report two slightly different methods of turning silicon into a thermoelectric material comparable with the best commercial materials. Currently these materials are made using exotic and expensive elements like bismuth and tellurium. The thermoelectric effect occurs when a material is heated and electrons flow from the hot to cold. This requires a material with strange characteristics – good electrical conductivity and poor heat conductivity so that the heat gradient can be maintained.

Silicon normally conducts heat much too well to be any use as a thermoelectric material. To overcome this, the two groups produced nanoscale silicon wires, reducing silicon’s conductivity one hundred-fold. As the wires are so tiny a combination of the roughness of the wires and their tiny diameter cut heat flow substantially but still allowed electrons to flow (Nature 2008, 451, 163-7 ; 168-171).

Silicon would be an ideal thermoelectrics candidate as it is cheap and a substantial infrastructure is already in place for handling and manufacturing it compared with current thermoelectric materials.

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