Si and Ge allotrope heterostructured nanowires: experimental evaluation of the thermal conductivity reduction

We have studied the thermal conductivity of Ge and Si allotrope heterostructured nanowires ( NWs) synthesized by phase transformation. The NWs are composed of successive hexagonal 2H and cubic diamond 3C crystal phases along the < 111 > axis. Using 3 omega-scanning thermal microscopy on NWs embedded in a silica matrix, we present the first experimental evidence of thermal conductivity reduction in such allotrope 2H/3C heterostructured NWs. In Ge heterostructured 2H/3C NWs, similarly to homogeneous 3C NWs, we show a thermal conductivity reduction when the NW diameter decreases. In addition, in Si and Ge NWs, we observe a reduced thermal conductivity due to the heterostructuration 2H/3C. We evidence that the temperature of phase transformation, which influences the size and the number of 2H domains, can constitute an efficient parameter to tune the thermal conductivity.