Role of crystal structure and junction morphology on interface thermal conductance

Abstract

We argue that the relative thermal conductance between interfaces with different morphologies is controlled by crystal structure through M_min/M_c > 1, the ratio between the <i>minimum mode</i> count on either side M_min, and the <i>conserving modes</i> M_c that preserve phonon momentum transverse to the interface. Junctions with an added homogenous layer, “uniform,” and “abrupt” junctions are limited to M_c, while junctions with interfacial disorder, “mixed,” exploit the expansion of mode spectrum to M_min. In our studies with cubic crystals, the largest enhancement of conductance from “abrupt” to “mixed” interfaces seems to be correlated with the emergence of voids in the conserving modes, where M_c = 0. Such voids typically arise when the interlayer coupling is weakly dispersive, making the bands shift rigidly with momentum. Interfacial mixing also increases alloy scattering, which reduces conductance in opposition with the mode spectrum expansion. Thus the conductance across a “mixed” junction does not always increase relative to that at a “uniform” interface.