Low thermal conductivity in nanoscale layered materials synthesized by the method of modulated elemental reactants

We report the roomerature, cross-plane thermal conductivities, and longitudinal speeds of sound of multilayer films [(TiTe2) 3 (Bi2 Te3) x (TiTe2) 3 (Sb2 Te3) y] i (x=1-5, y=1-5) and misfit-layer dichalcogenide films [(PbSe) m (T Se2) n] i (T=W or Mo, m=1-5, and n=1-5) synthesized by the modulated elemental reactants method. The thermal conductivities of these nanoscale layered materials fall below the predicted minimum thermal conductivity of the component compounds: two times lower than the minimum thermal conductivity of Bi2 Te3 for multilayer [(TiTe2) 3 (Bi2 Te3) x (TiTe2) 3 (Sb2 Te3) y] i films and five to six times lower than the minimum thermal conductivity of PbSe for misfit-layer dichalcogenides [(PbSe) m (TSe2) n] i. We attribute the low thermal conductivities to the anisotropic bonding of the layered crystals and orientational disorder in the stacking of layered crystals along the direction perpendicular to the surface.