Wang Chiao-Tzu, Jiang Bei, Zhou Ya-Wei, Jiang Tian-Wen, Liu Jian-Hua, Zhu Guo-Dong, Cai Wen-Bin
Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Collaborative Innovation Center of Chemistry for Energy Materials, Department of Chemistry , Fudan University , Shanghai 200433 , People's Republic of China.
Department of Optical Science and Engineering , Fudan University , Shanghai , People's Republic of China.
Anal Chem. 2019 Aug 20;91(16):10541-10548. doi: 10.1021/acs.analchem.9b01554. Epub 2019 Jul 31.
The photothermally induced resonance AFM-IR technique (denoted as PTIR) is a promising and still developing analytical method that can provide nanoscale chemical and topographical information. Herein, by taking advantage of a customized PTIR system with either top-down or bottom-up incidence mode for a quantum cascade laser (QCL), we explore how the surface-enhanced IR absorption (SEIRA) effect due to the Au-coated AFM tip and/or substrate may affect the PTIR signals from 25 to 580 nm thick -nitrobenzoic acid (PNBA) samples, as a function of sample thickness, incidence mode, laser polarization, and Au film morphology. By analysis of the ν(NO) band intensity, it is revealed that the SEIRA effect may increase the PTIR signals by 1.5-8.3 times, with that from the Au-coated substrate being greater than that from the Au-coated tip. Nevertheless, the overall PTIR signal goes up monotonically over the entire thickness range for the top-down incidence mode, while it increases and then decreases with the sample thickness for the bottom-up incidence mode. The -polarized laser enhances the PTIR signal more than does the -polarized laser, especially on the Au-coated substrate. The significant loss of the PTIR signal of a PNBA sample corroborates the substantial loss of the SEIRA effect of an annealed Au film. The present work may promote the application of the SEIRA effect to the PTIR technique and provides hints for developing the PTIR technique into a more versatile analytical tool.
光热诱导共振原子力显微镜红外技术（简称为PTIR）是一种很有前景且仍在发展的分析方法，它能够提供纳米级的化学和形貌信息。在此，我们利用定制的PTIR系统，该系统针对量子级联激光器（QCL）具有自上而下或自下而上的入射模式，探讨由于涂金原子力显微镜探针和/或基底导致的表面增强红外吸收（SEIRA）效应如何影响厚度在25至580纳米之间的对硝基苯甲酸（PNBA）样品的PTIR信号，这是样品厚度、入射模式、激光偏振和金膜形态的函数。通过分析ν(NO)带强度发现，SEIRA效应可能会使PTIR信号增强1.5至8.3倍，涂金基底产生的增强效应大于涂金探针产生的。然而，对于自上而下的入射模式，整个厚度范围内的总体PTIR信号单调上升，而对于自下而上的入射模式，PTIR信号随样品厚度先增加后减小。与偏振激光相比，偏振激光对PTIR信号的增强作用更大，尤其是在涂金基底上。PNBA样品PTIR信号的显著损失证实了退火后金膜SEIRA效应的大幅损失。本工作可能会推动SEIRA效应在PTIR技术中的应用，并为将PTIR技术发展成为更通用的分析工具提供线索。
