Ultra-low thermal conductivity of high-interface density Si/Ge amorphous multilayers

Owing to their phonon scattering and interfacial thermal resistance (ITR) characteristics, inorganic multilayers (MLs) have attracted considerable attention for thermal barrier applications. In this study, a-Si/a-Ge MLs with layer thicknesses ranging from 0.3 to 5 nm and different interfacial elemental mixture states were fabricated using a combinatorial sputter-coating system, and their thermal conductivities were measured via a frequency-domain thermo-reflectance method. An ultra-low thermal conductivity of κ = 0.29 ± 0.01 W K^-1 m^-1 was achieved for a layer thickness of 0.8 nm. The ITR was found to decrease from 8.5 × 10^-9 to 3.6 × 10^-9 m² K W^-1 when the interfacial density increases from 0.15 to 0.77 nm^-1.