National ESCA and Surface Analysis Center for Biomedical Problems, Department of Chemical Engineering, P.O. Box 351750, University of Washington, Seattle, Washington 98195, USA.
Anal Chem. 2011 Sep 1;83(17):6704-12. doi: 10.1021/ac201175a. Epub 2011 Jul 26.
Quantitative analysis of the 16-mercaptohexadecanoic acid self-assembled monolayer (C16 COOH-SAM) layer thickness on gold nanoparticles (AuNPs) was performed using simulation of electron spectra for surface analysis (SESSA) software and X-ray photoelectron spectroscopy (XPS) experimental measurements. XPS measurements of C16 COOH-SAMs on flat gold surfaces were made at nine different photoelectron emission angles (5-85° in 10° increments), corrected using geometric weighting factors and then summed together to approximate spherical AuNPs. The SAM thickness and relative surface roughness (RSA) in SESSA were optimized to determine the best agreement between simulated and experimental surface composition. On the basis of the glancing-angle results, it was found that inclusion of a hydrocarbon-contamination layer on top the C16 COOH-SAM was necessary to improve the agreement between the SESSA and XPS results. For the 16 COOH-SAMs on flat Au surfaces, using a SAM thickness of 1.1 Å/CH(2) group, an RSA of 1.05, and a 1.5 Å CH(2)-contamination overlayer (total film thickness = 21.5 Å) for the SESSA calculations provided the best agreement with the experimental XPS data. After applying the appropriate geometric corrections and summing the SESSA flat-surface compositions, the best fit results for the 16 COOH-SAM thickness and surface roughness on the AuNPs indicated a slightly thinner overlayer with parameters of 0.9 Å/CH(2) group in the SAM, an RSA of 1.06 RSA, and a 1.5 Å CH(2)-contamination overlayer (total film thickness = 18.5 Å). The 3 Å difference in SAM thickness between the flat Au and AuNP surfaces suggests that the alkyl chains of the SAM are slightly more tilted or disordered on the AuNP surfaces.
使用表面分析电子能谱模拟 (SESSA) 软件和 X 射线光电子能谱 (XPS) 实验测量对金纳米粒子 (AuNP) 上 16-巯基十六烷酸自组装单分子层 (C16COOH-SAM) 的厚度进行了定量分析。在九个不同的光电子发射角度 (以 10°的增量从 5°到 85°) 下对 Au 表面上的 C16COOH-SAM 进行了 XPS 测量，使用几何加权因子进行了修正，然后将它们加在一起以近似球形的 AuNP。在 SESSA 中优化了 SAM 厚度和相对表面粗糙度 (RSA)，以确定模拟和实验表面组成之间的最佳一致性。根据掠角结果，发现需要在 C16COOH-SAM 顶部包含一层碳氢化合物污染层，以提高 SESSA 和 XPS 结果之间的一致性。对于 Au 表面上的 16COOH-SAMs，使用 1.1 Å/CH(2) 组的 SAM 厚度、1.05 的 RSA 和 1.5 Å 的 CH(2)-污染覆盖层 (总膜厚 = 21.5 Å) 进行 SESSA 计算，与实验 XPS 数据提供了最佳的一致性。在应用适当的几何修正并对 SESSA 平面组成进行求和后，对于 AuNP 上的 16COOH-SAM 厚度和表面粗糙度，最佳拟合结果表明覆盖层略薄，SAM 中每个 CH(2) 组的参数为 0.9 Å，RSA 为 1.06 RSA，CH(2)-污染覆盖层为 1.5 Å (总膜厚 = 18.5 Å)。在平面 Au 和 AuNP 表面之间，SAM 厚度的 3 Å 差异表明，SAM 的烷基链在 AuNP 表面上稍微倾斜或无序。
