Department of Chemistry and Biochemistry , Texas Tech University , Lubbock , Texas 79409 , United States.
Department of Chemistry , University of Utah , Salt Lake City , Utah 84112 , United States.
Anal Chem. 2019 Jan 2;91(1):1049-1055. doi: 10.1021/acs.analchem.8b04390. Epub 2018 Dec 13.
Single layer graphene (SLG), with its angstrom-scale thickness and strong Raman scattering cross section, was adapted for measurement of the axial ( Z-direction) probe beam profile in confocal Raman microscopy depth-profiling experiments. SLG adsorbed to a glass microscope coverslip (SLG/SiO) served as a platform for the estimation of axial spatial resolution. Profiles were measured by stepping the confocal probe volume through the SLG/SiO interface while measuring Raman scattering from the sample. Using a high numerical aperture (1.4 NA) oil immersion objective, axial profiles were derived from the graphene 2D vibrational mode and fit to a Lorentzian instrument response function (IRF). Subsequently, the Z-direction spatial resolution in depth-profiling studies of polymer interfaces was estimated through convolution of the Lorentzian IRF with a step function representing the ideal junction separating the phases of interest. In the study of a bipolar polymer membrane, confocal Raman depth profiles of the AEM/CEM (anion exchange membrane/cation exchange membrane) interface show that the transition region is broader than the limiting response and are consistent with roughness at the boundary on the order of a few micrometers. Using ClO as a Raman active mobile ion probe, application of self-modeling curve resolution (SMCR) to spectral data sets within a profile showed ClO ions track the spatial distribution of the AEM phase. Finally, in measurements on a liquid-solid interface formed between 1-octanol and a polydimethylsiloxane (PDMS) membrane, the IRF derived from fitting the experimental profile was slightly narrower than those obtained from profiling SLG, indicating the potential to use polymer-liquid interfaces formed from widely available materials and reagents for estimation of axial spatial resolution in confocal Raman depth-profiling.
单层石墨烯（SLG）具有埃米级厚度和较强的拉曼散射截面，适用于共焦拉曼显微镜深度剖析实验中轴向（Z 方向）探针光束轮廓的测量。吸附在玻璃显微镜盖玻片上的 SLG（SLG/SiO）用作估计轴向空间分辨率的平台。通过在测量样品的拉曼散射时，将共焦探针体积穿过 SLG/SiO 界面进行扫描，从而测量轮廓。使用高数值孔径（1.4 NA）油浸物镜，从石墨烯 2D 振动模式得出轴向轮廓，并拟合洛伦兹仪器响应函数（IRF）。随后，通过将洛伦兹 IRF 与代表感兴趣相之间理想交界的阶跃函数卷积，估算聚合物界面深度剖析中 Z 方向的空间分辨率。在双极聚合物膜的研究中，AEM/CEM（阴离子交换膜/阳离子交换膜）界面的共焦拉曼深度轮廓显示，过渡区域比极限响应宽，与边界处的粗糙度一致，约为几个微米。使用 ClO 作为拉曼活性移动离子探针，在轮廓内的光谱数据集上应用自建模曲线分辨率（SMCR）表明，ClO 离子跟踪 AEM 相的空间分布。最后，在 1-辛醇和聚二甲基硅氧烷（PDMS）膜之间形成的液-固界面的测量中，从拟合实验轮廓得出的 IRF 略窄于从 SLG 轮廓得出的 IRF，这表明有可能利用广泛可用的材料和试剂形成的聚合物-液体界面来估计共焦拉曼深度剖析中的轴向空间分辨率。
