Infrared (IR) spectroscopy is a powerful technique to characterize the chemical structure and dynamics of various types of samples. However, the signal-to-noise-ratio drops rapidly when the sample thickness gets much smaller than penetration depth, which is proportional to wavelength. This poses serious problems in analysis of thin films. In this work, an approach is demonstrated to overcome these problems. It is shown that a standard IR spectroscopy can be successfully employed to study the structure and composition of films as thin as 20 nm, when the layers were grown on porous substrates with a well-developed surface area. In contrast to IR spectra of the films deposited on flat Si substrates, the IR spectra of the same films but deposited on porous ceramic support show distinct bands that enabled reliable chemical analysis. The analysis of Zn-S ultrathin films synthesized by atomic layer deposition (ALD) from diethylzinc (DEZ) and 1,5-pentanedithiol (PDT) as precursors of Zn and S, respectively, served as proof of concept. However, the approach presented in this study can be applied to analysis of any ultrathin film deposited on target substrate and simultaneously on porous support, where the latter sample would be a reference sample dedicated for IR analysis of this film.

中文翻译：

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多孔AAO陶瓷载体上沉积Zn-S杂化和ZnS超薄膜的红外吸收研究

红外（IR）光谱是一种强大的技术，可表征各种类型样品的化学结构和动力学。但是，当样品厚度远小于与波长成比例的穿透深度时，信噪比迅速下降。这在薄膜分析中提出了严重的问题。在这项工作中，展示了一种克服这些问题的方法。结果表明，当将层生长在表面积充分发达的多孔基板上时，可以成功地使用标准的红外光谱研究薄至20 nm的膜的结构和组成。与沉积在平坦Si衬底上的薄膜的IR光谱相反，相同薄膜但沉积在多孔陶瓷载体上的IR光谱显示出不同的谱带，从而能够进行可靠的化学分析。通过原子层沉积（ALD）分别由二乙基锌（DEZ）和1,5-戊二硫醇（PDT）分别作为Zn和S的前体合成的Zn-S超薄膜的分析证明了这一概念。但是，本研究中介绍的方法可用于分析沉积在目标基材上并同时沉积在多孔载体上的任何超薄薄膜，后者的样品将是用于对该膜进行IR分析的参考样品。