Abstract Inelastic electron tunneling spectroscopy (IETS) combined with scanning tunneling microscopy (STM) allows the acquisition of vibrational signals at surfaces. In STM-IETS, a tunneling electron may excite a vibration, and opens an inelastic channel in parallel with the elastic one, giving rise to a change in conductivity of the STM junction. Until recently, the application of STM-IETS was limited to the localized vibrations of single atoms and molecules adsorbed on surfaces. The theory of the STM-IETS spectrum in such cases has been established. For the collective lattice dynamics, i.e., phonons, however, features of STM-IETS spectrum have not been understood well, though in principle STM-IETS should also be capable of detecting phonons. In this review, we present STM-IETS investigations for surface and interface phonons and provide a theoretical analysis. We take surface phonons on Cu(1 1 0) and interfacial phonons relevant to graphene on SiC substrate as illustrative examples. In the former, we provide a theoretical formalism about the inelastic phonon excitations by tunneling electrons based on the nonequilibrium Green’s function (NEGF) technique applied to a model Hamiltonian constructed in momentum space for both electrons and phonons. In the latter case, we discuss the experimentally observed spatial dependence of the STM-IETS spectrum and link it to local excitations of interfacial phonons based on ab-initio STM-IETS simulation.

中文翻译：

---

固体表面和界面声子的 STM 非弹性电子隧穿光谱

摘要 非弹性电子隧道光谱 (IETS) 与扫描隧道显微镜 (STM) 相结合，可以采集表面的振动信号。在 STM-IETS 中，隧穿电子可能会激发振动，并打开与弹性通道平行的非弹性通道，导致 STM 结的电导率发生变化。直到最近，STM-IETS 的应用仅限于吸附在表面上的单个原子和分子的局部振动。在这种情况下，STM-IETS 频谱的理论已经建立。然而，对于集体晶格动力学，即声子，STM-IETS 光谱的特征还没有得到很好的理解，尽管原则上 STM-IETS 也应该能够检测声子。在这次审查中，我们展示了 STM-IETS 对表面和界面声子的研究，并提供了理论分析。我们以 Cu(1 1 0) 上的表面声子和 SiC 衬底上与石墨烯相关的界面声子为例。在前者中，我们基于非平衡格林函数 (NEGF) 技术提供了关于隧道电子的非弹性声子激发的理论形式，该技术应用于在动量空间中为电子和声子构建的模型哈密顿量。在后一种情况下，我们讨论了实验观察到的 STM-IETS 光谱的空间依赖性，并将其与基于 ab-initio STM-IETS 模拟的界面声子的局部激发联系起来。基于非平衡格林函数 (NEGF) 技术，我们提供了关于隧道电子的非弹性声子激发的理论形式，该技术应用于在动量空间中为电子和声子构建的模型哈密顿量。在后一种情况下，我们讨论了实验观察到的 STM-IETS 光谱的空间依赖性，并将其与基于 ab-initio STM-IETS 模拟的界面声子的局部激发联系起来。基于非平衡格林函数 (NEGF) 技术，我们提供了关于隧道电子的非弹性声子激发的理论形式，该技术应用于在动量空间中为电子和声子构建的模型哈密顿量。在后一种情况下，我们讨论了实验观察到的 STM-IETS 光谱的空间依赖性，并将其与基于 ab-initio STM-IETS 模拟的界面声子的局部激发联系起来。