Atomically localized ingredient-dependent interface phonon in heterogeneous solids

Phonons are the primary heat carriers in non-metallic solids. In compositionally heterogeneous materials, the thermal properties are believed to be mainly governed by the disrupted phonon transport due to mass disorder and strain fluctuations, while the effects of compositional fluctuation induced local phonon states are usually ignored. Here, by scanning transmission electron microscopy electron energy loss spectroscopy and sophisticated calculations, we identify the vibrational properties of ingredient-dependent interface phonon modes in Al x Ga 1-x N and quantify their various contributions to the local interface thermal conductance. We demonstrate that atomic-scale compositional fluctuation has significant influence on the vibrational thermodynamic properties, highly affecting the mode ratio and vibrational amplitude of interface phonon modes and subsequently redistributing their modal contribution to the ITC. Our work provides fundamental insights into understanding of local phonon-boundary interactions in nanoscale inhomogeneities, which reveal new opportunities for optimization of thermal properties via engineering ingredient distribution. mode numbers and amplitude of those localized modes at the interface, subsequently contributing smaller to ITC. Besides to the well-established knowledge of effects of mass disorder and strain fluctuations on local thermal properties, this work suggests that the compositional interface also play an important role in the local thermal conductivity. The tunable interfacial thermal characteristics via compositional fluctuations tailoring interface phonon modes also provide new insights into the engineering of thermal properties in heat dissipation and energy conversion materials and devices.