Surface phonon polaritons (SPhPs) are coupled photon-phonon excitations that emerge at the surfaces of nanostructured materials. Although they strongly influence the optical and thermal behavior of nanomaterials, no technique has been able to reveal the complete three-dimensional (3D) vectorial picture of their electromagnetic density of states. Using a highly monochromated electron beam in a scanning transmission electron microscope, we could visualize varying SPhP signatures from nanoscale MgO cubes as a function of the beam position, energy loss, and tilt angle. The SPhPs’ response was described in terms of eigenmodes and used to tomographically reconstruct the phononic surface electromagnetic fields of the object. Such 3D information promises insights in nanoscale physical phenomena and is invaluable to the design and optimization of nanostructures for fascinating new uses.

表面声子极化子（SPhPs）是耦合的​​光子-声子激发，出现在纳米结构材料的表面。尽管它们强烈影响纳米材料的光学和热行为，但尚无技术能够揭示其电磁态的完整三维（3D）矢量图像。在扫描透射电子显微镜中使用高度单色的电子束，我们可以可视化来自纳米级MgO立方体的变化的SPhP标记，这些特征是束位置，能量损失和倾斜角的函数。SPhPs的响应以本征模式进行描述，并用于以断层摄影法重建对象的声子表面电磁场。