Accurate and simple measurements of the thermal conductivity of thin films deposited on high thermal conductivity substrates have been recently enabled by the development of an AC hot-wire method, the 3ω method. Recent progress in the measurement and understanding of heat transport in ultra-thin films (1 μm thick) and multilayers is reviewed, and the possibility of using solid-solid interfaces on nanometer length scales to control heat transport in thin film materials is explored. The finite thermal conductance of solid-solid interfaces becomes important when considering heat transport in single layer films < 100 nm thick. Through the use of multilayer films-for example, epitaxial superlattices of crystalline semiconductors or nanometer-thick layers of amorphous and microcrystalline oxides-we can study materials with an extremely high and controllable density of internal interfaces, and evaluate the effect of these interfaces on heat transport. For the case of Si-Ge superlattices, the relatively large mismatch of the vibrational properties of silicon and germanium creates a larger reduction in thermal conductivity than for GaAs-AlAs superlattices. Surprisingly, heat conduction in multilayers of disordered oxides is essentially unchanged by a high interface density.
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Cahill et al. (2000) studied this question.