Heat transfer across nanoscale metal/dielectric multilayers involves multiple thermal conduction mechanisms. Electron or phonon interface scattering can augment the thermal conductivity anisotropy in multilayer composites. Weak electron-phonon coupling and quasi-ballistic phonon transport normal to the metal film further increase the anisotropy for metal-dielectric multilayers with period shorter than the relevant free paths. This paper models these physical mechanisms using an approximate thermal resistor network with support from the Boltzmann transport equation. We measure the in- and cross-plane thermal conductivity of a Mo/Si (2.8 nm/4.1 nm) multilayer as 15.4 and 1.2 W/mK, respectively, which agree with the proposed theoretical model. This work introduces a criterion for the transition from electron to phonon dominated heat conduction in metal films bounded by dielectrics.

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