Monolayers at solid–solid interfaces probed with infrared spectroscopy
Monolayers at solid–solid interfaces probed with infrared spectroscopy
复制标题
用红外光谱探测固-固界面处的单分子层
DOI：
10.1007/s00216-006-1010-4
复制
发表时间：
2007
影响因子：
4.3
通讯作者：
H. Hoffmann
中科院分区：
文献类型：
--
作者：
T. Lummerstorfer;J. Kattner;H. Hoffmann
采用高折射率的入射光介质，如红外透明固体材料，可以大大提高薄吸附层在透射、内反射或外反射下红外光谱的灵敏度。这种灵敏度的增加是由于夹在两种高折射率材料之间的低折射率薄层中的垂直电场的强烈增强。基于对一个假想样品层的模型计算，研究了入射角、样品层厚度和层间光学接触等实验参数的影响和优化。在优化的条件下，这种增强可以超过100的因素相比，传统的表面红外技术。此外，夹层样品层的光谱是由一个统一的表面选择规则，这样，只有垂直的振动分量得到增强，它们允许一个简单的，基板独立的表面取向分析。单层光谱的长链烃类化合物吸附到金和硅基板上，并与锗晶体作为入射介质接触的实验例子表明，这种三明治技术的简单的实验实现和前所未有的灵敏度，他们提供了新的见解的化学和结构的单层限制和压缩之间的两个固体表面。
图：夹在硅和锗之间的脂肪酸甲酯单层膜的红外反射光谱。
AbstractThe sensitivities of infrared spectra of thin adsorbate layers measured in either transmission, internal reflection or external reflection can be greatly increased if a light incidence medium with a high refractive index such as an IR-transparent solid material is used. This increase in sensitivity is due to the strong enhancement of the perpendicular electric field in a thin layer of low refractive index sandwiched between two high refractive index materials. Based on model calculations of a hypothetical sample layer, the influence and optimization of experimental parameters such as incidence angle, sample layer thickness and optical contact between layers are investigated. Under optimized conditions, this enhancement can exceed a factor of 100 when compared to conventional surface IR techniques. In addition, the spectra of sandwiched sample layers are governed by a uniform surface selection rule, such that only the perpendicular vibrational components are enhanced, and they permit a straightforward, substrate-independent analysis of surface orientations. Experimental examples of monolayer spectra of long-chain hydrocarbon compounds adsorbed onto gold and silicon substrates and contacted with a germanium crystal used as the incidence medium demonstrate the simple experimental realization and unprecedented sensitivity of this sandwich technique, and they offer novel insights into the chemistry and structure of monolayers confined and compressed between two solid surfaces.
FigureIR reflection spectrum of a monolayer of a fatty acid methyl ester sandwiched between silicon and germanium.