表面声子的三维矢量成像
Three dimensional vectorial imaging of surface phonons
摘要：
虽然声子和它们的相关性质已经在块体材料中得到了全面的研究，但对纳米级物体表面声子的透彻理解仍然是难以捉摸的。使用光子或电子的红光成像方法存在，可以将这些振动激发映射到单个原子尺度。然而，到目前为止，还没有技术能够直接揭示纳米结构物体的声子电磁态密度的完整三维矢量图。在扫描透射电子显微镜中使用高度单色化的电子束，我们可以将来自纳米级MgO立方体的不同声子签名可视化为束位置、能量损失和倾斜角的函数。的振动响应被描述在定义良好的本征模式，并被用来断层重建的声子表面场的对象，揭示了传统的映射不可见的效果。表面声子的应用主要依赖于电磁场的空间和矢量形状，强烈影响材料的光学，热和电子行为。因此，这种3D信息有望在纳米级物理现象的新见解，是非常宝贵的纳米结构的设计和优化迷人的新用途。
英文摘要：
While phonons and their related properties have been studied comprehensively in bulk materials, a thorough understanding of surface phonons for nanoscale objects remains elusive. Infra-red imaging methods with photons or electrons exist, which can map these vibrational excitations down to the individual atom scale. However, no technique so far was able to directly reveal the complete three-dimensional vectorial picture of the phononic electromagnetic density of states from a nanostructured object. Using a highly monochromated electron beam in a scanning transmission electron microscope, we could visualize varying phonon signatures from nanoscale MgO cubes both as a function of the beam position, energy-loss and tilt angle. The vibrational responses were described in terms of well-defined eigenmodes and were used to tomographically reconstruct the phononic surface fields of the object, disclosing effects invisible by conventional mapping. Surface phonon applications rely critically on the way the electromagnetic field is spatially and vectorially shaped, strongly influencing the optical, thermal and electronic behavior of the materials. Such 3D information therefore promises novel insights in nanoscale physical phenomena and is invaluable to the design and optimization of nanostructures for fascinating new uses.
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