Nanostructured Interfaces for Thermoelectrics

Temperature drops at the interfaces between thermoelectric materials and the heat source and sink reduce the overall efficiency of thermoelectric systems. Nanostructured interfaces based on vertically aligned carbon nanotubes (CNTs) promise the combination of mechanical compliance and high thermal conductance required for thermoelectric modules, which are subjected to severe thermomechanical stresses. This work discusses the property require- ments for thermoelectric interface materials, reviews relevant data available in the literature for CNT films, and characterizes the thermal properties of vertically aligned multiwalled CNTs grown on a candidate thermoelectric material. Nanosecond thermoreflectance thermometry provides thermal property data for 1.5-μm-thick CNT films on SiGe. The thermal interface resistances between the CNT film and surrounding materials are the dominant barriers to thermal transport, ranging from 1.4 m2 K MW−1 to 4.3 m2 K MW−1. The volumetric heat capacity of the CNT film is estimated to be 87 kJ m−3 K−1, which corresponds to a volumetric fill fraction of 9%. The effect of 100 thermal cycles from 30°C to 200°C is also studied. These data provide the groundwork for future studies of thermoelectric materials in contact with CNT films serving as both a thermal and electrical interface.