Realization of crystal silicon with world’s smallest thermal conductivity
-Novel thermoelectric material for reuse of waste heat-

Ecofriendly and low-cost thermoelectric materials with high performance are needed for the use of thermoelectric conversion as safe and clean energy source in human society. A key point to obtain high thermoelectric performance is to achieve low thermal conductivity in materials. We achieved anomalously low thermal conductivity in nanometer-sized structure composed of nanodot crystals of ubiquitous element, Si. This structure exhibited 1/200 times reduction in thermal conductivity compared with macroscopic crystal Si. This result can be evolved to development of ecofriendly and low-cost thermoelectric material. Furthermore, because Si is an electronic device material, this result can bring the possibility to realize the Si electronic devises with function of thermoelectric conversion from a low-temperature waste heat of personal computer or server into electrical energy.