Nano-FTIR spectroscopy based on Fourier transform infrared near-field spectroscopy allows for label-free chemical nanocharacterization of organic and inorganic composite surfaces. The potential capability for subsurface material analysis, however, is largely unexplored terrain. Here, we demonstrate nano-FTIR spectroscopy of subsurface organic layers, revealing that nano-FTIR spectra from thin surface layers differ from that of subsurface layers of the same organic material. Further, we study the correlation of various nano-FTIR peak characteristics and establish a simple and robust method for distinguishing surface from subsurface layers without the need of theoretical modeling or simulations (provided that chemically induced spectral modifications are not present). Our experimental findings are confirmed and explained by a semi-analytical model for calculating nano-FTIR spectra of multilayered organic samples. Our results are critically important for the interpretation of nano-FTIR spectra of multilayer samples, particularly to avoid that geometry-induced spectral peak shifts are explained by chemical effects.

基于傅立叶变换红外近场光谱的纳米FTIR光谱技术可实现有机和无机复合材料表面的无标记化学纳米表征。但是，地下材料分析的潜在能力在很大程度上是未开发的地形。在这里，我们展示了地下有机层的纳米FTIR光谱，揭示了来自薄表面层的纳米FTIR光谱不同于同一有机材料的地下层的纳米FTIR光谱。此外，我们研究了各种纳米FTIR峰特征的相关性，并建立了一种简单而鲁棒的方法来区分表面和地下层，而无需进行理论建模或模拟（前提是不存在化学诱导的光谱修饰）。我们的实验结果得到了用于计算多层有机样品的纳米FTIR光谱的半分析模型的证实和解释。我们的结果对于解释多层样品的纳米FTIR光谱至关重要，特别是要避免由几何效应解释由几何引起的光谱峰移。