Theory of Midinfrared Absorption Microspectroscopy: I. Homogeneous Samples
Theory of Midinfrared Absorption Microspectroscopy: I. Homogeneous Samples
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DOI：
10.1021/ac902067p
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发表时间：
2010-05-01
影响因子：
7.4
通讯作者：
Bhargava, Rohit
中科院分区：
文献类型：
--
作者：
Davis, Brynmor J.;Carney, P. Scott;Bhargava, Rohit
中红外 (IR) 显微光谱广泛应用于空间局部光谱分析。然而，之前尚未提出该技术的综合理论模型。在本文中，通过使用麦克斯韦方程来模拟光束传播，提出了红外吸收显微光谱学的严格理论。考虑聚焦效应、材料色散和样品的几何形状来预测均匀样品的光谱响应。使用光刻胶的傅里叶变换红外 (FT-IR) 显微光谱检查对预测进行了实验验证。结果强调，对红外显微光谱数据的有意义的解释必须涉及对与样品、基材特性和显微镜配置相关的耦合光学效应的理解。模拟通过量化记录数据的失真为开发实验方法和未来仪器设计提供指导。对于透反射模式和安装在某些基板上的样品来说，畸变尤其严重。最后，该模型概括为严格考虑聚焦的影响。虽然光谱分析的范围从检查总体光谱特征到使用先进的化学计量学评估细微特征，但数据采集中的这些影响对可用信息造成的限制尚不清楚。失真效应被证明比现代光谱仪中看到的噪声水平更大。因此，该模型提供了一个量化光谱失真的框架，这些失真可能会限制信息的准确性或在显微光谱学中出现混杂效应。
Midinfrared (IR) microspectroscopy is widely employed for spatially localized spectral analyses. A comprehensive theoretical model for the technique, however, has not been previously proposed. In this paper, rigorous theory is presented for IR absorption microspectroscopy by using Maxwell's equations to model beam propagation. Focusing effects, material dispersion, and the geometry of the sample are accounted to predict spectral response for homogeneous samples. Predictions are validated experimentally using Fourier transform IR (FT-IR) microspectroscopic examination of a photoresist. The results emphasize that meaningful interpretation of IR microspectroscopic data must involve an understanding of the coupled optical effects associated with the sample, substrate properties, and microscopy configuration. Simulations provide guidance for developing experimental methods and future instrument design by quantifying distortions in the recorded data. Distortions are especially severe for transflection mode and for samples mounted on certain substrates. Last, the model generalizes to rigorously consider the effects of focusing. While spectral analyses range from examining gross spectral features to assessing subtle features using advanced chemometrics, the limitations imposed by these effects in the data acquisition on the information available are less clear. The distorting effects are shown to be larger than noise levels seen in modern spectrometers. Hence, the model provides a framework to quantify spectral distortions that may limit the accuracy of information or present confounding effects in microspectroscopy.