Silicon nanowires turn heat into power

A newly discovered type of silicon nanowire could lead to personal 'power-jackets' that use heat from the human body to charge electronic devices.

The Lawrence Berkeley National Laboratory and the University of California at Berkeley revealed details of the far-ranging potential applications of these nanowires which they have synthesised using a new technique.

The nanowires demonstrate high performance thermoelectric properties even at room temperature when connected between two suspended heating pads.

"This is the first demonstration of high performance thermoelectric capability in silicon," said Arun Majumdar, a mechanical engineer and materials scientist with joint appointments at Berkeley Lab and UC Berkeley.

Peidong Yang, the other principal investigator behind this research, added: "We have shown that it is possible to achieve a large enhancement of thermoelectric energy efficiency at room temperature in rough silicon nanowires that have been processed by wafer-scale electrochemical synthesis."

Majumdar and Yang are the co-authors of a paper appearing in the 10 January edition of the journal Nature.

The paper describes a unique "electroless etching" method by which arrays of silicon nanowires are synthesised in an aqueous solution on the surfaces of wafers that can measure dozens of square inches in area.

The researchers explained that nearly all of the world's electrical power, approximately 10 trillion watts, is generated by gas or steam-powered turbines that convert heat to mechanical energy, which is then converted to electricity.

Much of this heat, approximately 15 trillion watts, is not converted but is released into the environment.

If even a small fraction of this lost heat could be converted to electricity, its impact on the energy situation would be enormous, the scientists claim.

"Thermoelectric materials, which have the ability to convert heat into electricity, could be used to capture much of the low-grade waste heat now being lost. This would result in massive savings on fuel and carbon dioxide emissions, " said Majumdar.

"The same devices can also be used as refrigerators and air conditioners and, because these devices can be miniaturised, it could make heating and cooling much more localised and efficient."