Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, China.
International Center for Quantum Materials, Peking University, Beijing, China.
Nature. 2021 Nov;599(7885):399-403. doi: 10.1038/s41586-021-03971-9. Epub 2021 Nov 17.
The breakdown of translational symmetry at heterointerfaces leads to the emergence of new phonon modes localized at the interface. 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 device. Although related theoretical work began decades ago, 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.
异质界面上平移对称性的破坏导致新的声子模式在界面处出现。这些模式在器件的热和电输运性质中起着重要作用，特别是在微型器件中，界面可能主导整个器件的响应。尽管相关的理论工作始于几十年前，但由于实现探测局域模式所需的空间、动量和光谱分辨率的综合挑战，实验研究完全是空白。在这里，我们使用四维电子能量损失谱技术，直接测量外延立方氮化硼/金刚石异质界面的局域振动谱和界面声子色散关系。除了体声波模式外，我们还观察到局域在界面上的模式和与界面隔离的模式。这些特征仅出现在界面附近约一纳米范围内。这里观察到的局域模式预计会极大地影响界面热导率和电子迁移率。我们的发现为异质界面上的晶格动力学提供了新的见解，所展示的实验技术应该在热管理、电气工程和拓扑声子学中有用。
