Enhanced thermal conductance at interfaces between gold and amorphous silicon and between gold and amorphous silica

Heat transfer at the interface between two materials is becoming increasingly important as the size of electronic devices shrinks. Most studies concentrate on the interfacial thermal conductance between either crystalline-crystalline or amorphous-amorphous materials. Here, we investigate the interfacial thermal conductance at crystalline-amorphous interfaces using nonequilibrium molecular dynamics simulations. Specifically, gold and two different materials, silicon and silica, in both their crystalline and amorphous structures, have been considered. The findings reveal that the interfacial thermal conductance between amorphous structures and gold is significantly higher as compared with crystalline structures for both planar and rough interfaces ($\ensuremath{\approx}152\phantom{\rule{4pt}{0ex}}\mathrm{MW}/({\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ for gold-amorphous silicon and $\ensuremath{\approx}56\phantom{\rule{4pt}{0ex}}\mathrm{MW}/({\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ for gold-crystalline silicon). We explain this increase by two factors: the relative commensurability between amorphous silicon or silica and gold leads to enhanced bonding and cross correlations of atomic displacements at the interface, contributing to enhance phonon elastic transmission. Inelastic phonon transmission is also enhanced due to the relative larger degree of anharmonicity characterizing gold-amorphous silicon or silica. We also show that all the vibrational modes that participate to interfacial heat transfer are delocalized and use the Ioffe-Regel (IR) criterion to separate the contributions of propagating (propagons) and nonpropagating modes (diffusons). In particular, we demonstrate that, while at gold-amorphous silicon interfaces elastic phonon scattering involves propagons and inelastic phonon scattering involves a mixture of propagons and diffusons, in gold-amorphous silica, all modes transmitting energy at the interface are diffusons. This study calls for the systematic experimental determination of the interfacial thermal conductance between amorphous materials and metals.