For decades, infrared (IR) spectroscopy has advanced on two distinct frontiers: enhancing spatial resolution and broadening spectroscopic information. Although atomic force microscopy (AFM)-based IR microscopy overcomes Abbe’s diffraction limit and reaches sub-10 nm spatial resolutions, time-domain two-dimensional IR spectroscopy (2DIR) provides insights into molecular structures, mode coupling and energy transfers. Here we bridge the boundary between these two techniques and develop AFM-2DIR nanospectroscopy. Our method offers the spatial precision of AFM in combination with the rich spectroscopic information provided by 2DIR. This approach mechanically detects the sample’s photothermal responses to a tip-enhanced femtosecond IR pulse sequence and extracts spatially resolved spectroscopic information via FFTs. In a proof-of-principle experiment, we elucidate the anharmonicity of a carbonyl vibrational mode. Further, leveraging the near-field photons’ high momenta from the tip enhancement for phase matching, we photothermally probe hyperbolic phonon polaritons in isotope-enriched h¹⁰BN. Our measurements unveil an energy transfer between phonon polaritons and phonons, as well as among different polariton modes, possibly aided by scattering at interfaces. The AFM-2DIR nanospectroscopy enables the in situ investigations of vibrational anharmonicity, coupling and energy transfers in heterogeneous materials and nanostructures, especially suitable for unravelling the relaxation process in two-dimensional materials at IR frequencies.

几十年来，红外 (IR) 光谱在两个不同的领域取得了进展：提高空间分辨率和拓宽光谱信息。尽管基于原子力显微镜 (AFM) 的红外显微镜克服了阿贝衍射极限并达到了 10 nm 以下的空间分辨率，但时域二维红外光谱 (2DIR) 提供了对分子结构、模式耦合和能量转移的深入了解。在这里，我们弥合了这两种技术之间的界限并开发了 AFM-2DIR 纳米光谱学。我们的方法提供了 AFM 的空间精度以及 2DIR 提供的丰富光谱信息。这种方法以机械方式检测样品对尖端增强飞秒红外脉冲序列的光热响应，并通过 FFT 提取空间分辨光谱信息。在原理验证实验中，我们阐明了羰基振动模式的非谐性。此外，利用尖端增强的近场光子高动量进行相位匹配，我们对富含同位素的 h ¹⁰ BN 中的双曲声子极化激元进行光热探测。我们的测量揭示了声子极化子和声子之间以及不同极化子模式之间的能量转移，这可能是通过界面处的散射来辅助的。 AFM-2DIR 纳米光谱能够对异质材料和纳米结构中的振动非谐性、耦合和能量转移进行原位研究，特别适合揭示红外频率下二维材料的弛豫过程。