Johns Hopkins University, Baltimore, USA
Engineering the thermal properties of semiconductors can benefit a wide range of applications. In particular, the performance of thermal management and thermoelectric generators could be enhanced by greater control over the thermal conductivity of materials. Such a control is possible via the nanostructure, which influences phononic properties. In this context, this seminar will present several studies of amorphous/crystalline silicon nanostructures. In amorphous materials, due to disorder, the vibrational contribution to thermal conductivity is different from that of crystals, and it is possible to distinguish the propagative or ballistic contribution from the diffusive contribution. These different contributions can be studied individually, in particular using a wave-packet approach on molecular dynamics models. In a first study, this categorization is applied to nanocomposites composed of crystalline nanoinclusions in an amorphous matrix. In particular, it is shown that while it is possible to manipulate the propagative contribution via the shape and interconnection of the inclusions, the diffusive contribution is more difficult to control. In a second step, the influence of an amorphous outer layer on a crystalline nanowire is studied by combining a molecular dynamics approach and a continuous media approach. It appears that the addition of the outer layer has little effect on the flux at the amorphous-crystalline interface, but does influence the heat flux at the center of the nanowire.