Department of Chemistry, University of Wisconsin-Madison , 1001 University Avenue, Madison, Wisconsin 53706, United States.
ACS Appl Mater Interfaces. 2015 Jan 28;7(3):1720-5. doi: 10.1021/am507300x. Epub 2015 Jan 15.
X-ray photoelectron spectroscopy (XPS) is a nearly universal method for quantitative characterization of both organic and inorganic layers on surfaces. When applied to nanoparticles, the analysis is complicated by the strong curvature of the surface and by the fact that the electron attenuation length can be comparable to the diameter of the nanoparticles, making it necessary to explicitly include the shape of the nanoparticle to achieve quantitative analysis. We describe a combined experimental and computational analysis of XPS data for molecular ligands on gold nanoparticles. The analysis includes scattering in both Au core and organic shells and is valid even for nanoparticles having diameters comparable to the electron attenuation length (EAL). To test this model, we show experimentally how varying particle diameter from 1.3 to 6.3 nm leads to a change in the measured AC/AAu peak area ratio, changing by a factor of 15. By analyzing the data in a simple computational model, we demonstrate that ligand densities can be obtained, and, moreover, that the actual ligand densities for these nanoparticles are a constant value of 3.9 ± 0.2 molecules nm(-2). This model can be easily extended to a wide range of core-shell nanoparticles, providing a simple pathway to extend XPS quantitative analysis to a broader range of nanomaterials.
X 射线光电子能谱（XPS）是一种几乎普遍适用于表面上有机和无机层的定量特性描述的方法。当应用于纳米粒子时，分析变得复杂，因为表面具有强烈的曲率，并且电子衰减长度可以与纳米粒子的直径相当，这使得必须明确包括纳米粒子的形状才能实现定量分析。我们描述了一种针对金纳米粒子上分子配体的 XPS 数据分析的组合实验和计算分析。该分析包括 Au 核和有机壳中的散射，并且即使对于直径与电子衰减长度（EAL）相当的纳米粒子也是有效的。为了测试该模型，我们通过实验展示了如何通过将粒径从 1.3nm 变化到 6.3nm，导致测量的 AC/AAu 峰面积比发生变化，变化幅度为 15 倍。通过在简单的计算模型中分析数据，我们证明可以获得配体密度，而且，这些纳米粒子的实际配体密度为 3.9±0.2 个分子 nm(-2)。该模型可以很容易地扩展到广泛的核壳纳米粒子范围，为将 XPS 定量分析扩展到更广泛的纳米材料提供了一种简单的途径。
