Large reduction in thermal conductivity for Ge quantum dots embedded in SiO2 system

Thermal conductivity (k(T)) of Ge quantum dots (QDs) embedded in SiO2 was investigated at T = 100–400 K. The Ge QD/SiO2 system appears to have much lower k(T) than their counterparts of bulk Ge and SiO2, and the reduction factor increases with the surface-to-volume ratio of the QD in SiO2. Attendant to reduced magnitude includes delayed Umklapp decline and weaker dependence on temperature for k(T). Effective medium analysis suggests the reduction in k primarily comes from the decreased group velocity thanks to the QD inclusion that induces interfacial stress on SiO2, phonon confinement, and boundary scatterings.