Precise thermal characterization of confined nanocrystalline silicon by a 3ω method

Due to a strong quantum confinement effect, the thermal conductivity and heat capacity per unit volume of a nanocrystalline silicon (nc-Si) layer prepared by electrochemical anodization are extremely lowered in comparison to those of single crystal silicon (c-Si). Based on this high contrast between the thermal properties of nc-Si and c-Si, we have developed novel thermally induced ultrasound emitter devices. The thermal insulating properties of the nc-Si layer play a key role in this case. This paper concerns precise measurements of the thermal conductivity and heat capacity per unit volume of the nc-Si layer using a dynamic approach called the 3 omega method. The measured thermal conductivity is 1.08 +/- 0.2 W/(m center dot K) in good agreement with that reported previously as measured by conventional techniques. The obtained heat capacity per unit volume of the nc-Si layer is, on the other hand I considerably smaller than that estimated from the porosity of the sample. These results provide useful information for designing an efficient ultrasound emitter.