Peak force infrared (PFIR) microscopy is an emerging atomic force microscopy (AFM)-based infrared microscopy that bypasses Abbe's diffraction limit on spatial resolution. The PFIR microscopy utilizes a nanoscopically sharp AFM tip to mechanically detect the tip-enhanced infrared photothermal response of the sample in the time domain. The time-gated mechanical signals of cantilever deflections transduce the infrared absorption of the sample, delivering infrared imaging and spectroscopy capability at sub 10 nm spatial resolution. Both the infrared absorption response and mechanical properties of the sample are obtained in parallel while preserving the surface integrity of the sample. This review describes the constructions of the PFIR microscope and several variations, including multiple-pulse excitation, total internal reflection geometry, dual-color configuration, liquid-phase operations, and integrations with simultaneous surface potential measurement. Representative applications of PFIR microscopy are also included in this review. In the outlook section, we lay out several future directions of innovations in PFIR microscopy and applications in chemical and material research.

中文翻译：

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峰值力红外显微镜原理及应用

峰值力红外 (PFIR) 显微镜是一种新兴的基于原子力显微镜 (AFM) 的红外显微镜，它绕过了阿贝对空间分辨率的衍射极限。PFIR 显微镜利用纳米级锐利的 AFM 尖端机械检测样品在时域中的尖端增强红外光热响应。悬臂偏转的时间门控机械信号可转换样品的红外吸收，提供低于 10 nm 空间分辨率的红外成像和光谱能力。同时获得样品的红外吸收响应和机械性能，同时保持样品的表面完整性。这篇综述描述了 PFIR 显微镜的结构和几种变体，包括多脉冲激发、全内反射几何、双色配置、液相操作以及与同时表面电位测量的集成。本综述还包括 PFIR 显微镜的代表性应用。在展望部分，我们列出了 PFIR 显微镜的几个未来创新方向以及在化学和材料研究中的应用。