The breakdown of translational symmetry at heterointerfaces leads to the emergence of new phonon modes localized at the interface¹. These modes have an essential role in thermal and electrical transport properties in devices, especially in miniature ones wherein the interface may dominate the entire response of the device². Although related theoretical work began decades ago^1,3,4,5, experimental research is totally absent owing to challenges in achieving the combined spatial, momentum and spectral resolutions required to probe localized modes. Here, using the four-dimensional electron energy-loss spectroscopy technique, we directly measure both the local vibrational spectra and the interface phonon dispersion relation for an epitaxial cubic boron nitride/diamond heterointerface. In addition to bulk phonon modes, we observe modes localized at the interface and modes isolated from the interface. These features appear only within approximately one nanometre around the interface. The localized modes observed here are predicted to substantially affect the interface thermal conductance and electron mobility. Our findings provide insights into lattice dynamics at heterointerfaces, and the demonstrated experimental technique should be useful in thermal management, electrical engineering and topological phononics.

异质界面处平移对称性的破坏导致出现在界面¹处的新声子模式。这些模式在器件中的热和电传输特性中具有重要作用，尤其是在其中界面可能支配器件²的整个响应的微型器件中。虽然相关的理论工作始于几十年前^1,3,4,5，由于在实现探测局部模式所需的组合空间、动量和光谱分辨率方面存在挑战，因此完全没有实验研究。在这里，我们使用四维电子能量损失光谱技术，直接测量外延立方氮化硼/金刚石异质界面的局部振动光谱和界面声子色散关系。除了体声子模式外，我们还观察到位于界面处的模式和与界面隔离的模式。这些特征只出现在界面周围大约一纳米的范围内。预计此处观察到的局部模式将显着影响界面热导率和电子迁移率。我们的研究结果提供了对异质界面晶格动力学的见解，