New approaches in the characterization of surface-enhanced Raman scattering-active substrates
New approaches in the characterization of surface-enhanced Raman scattering-active substrates
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DOI：
10.1002/(sici)1097-4555(199808)29:8
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发表时间：
1998-08
影响因子：
2.5
通讯作者：
N. Félidj;J. Aubard;G. Lévi
中科院分区：
文献类型：
--
作者：
N. Félidj;J. Aubard;G. Lévi
本文发展了一种新的表征表面增强拉曼散射(SERS)衬底的银胶和金胶的形貌的方法。由于电磁SERS理论和化学SERS理论都预测拉曼增强很大程度上依赖于表面粗糙度特征，因此要更好地理解SERS光谱和优化增强因子，就需要了解金属溶胶颗粒和团簇的尺寸和形状分布。为此，我们研究了两种原位技术。第一个涉及胶体金属颗粒的机械振动带(也称为声模)；如果表面等离子体共振激发增强，则可以在很低的拉曼波数移动(约10 cm-1)下观察到该带。这些声学模式的实验是在银胶和金胶上进行的，在几个激光激发波长下，在各种可极化分子(吡啶、吖啶、苯甲酸)或卤离子的存在下进行。由于这些声带的波数和形状与胶体颗粒的形态有关，因此使用先前开发的模型来计算声模分布，以接近引起SERS增强的粗糙度特征的尺寸和形状分布。由于金属胶体的消光、散射和吸收带是由表面等离子体共振激发产生的，因此紫外可见光谱也是分析胶体光学性质的有力工具。从观察到的银和金胶体的消光分布，用与低喇曼波数散射实验中使用的相同的探针分子聚集，试图获得各种聚集体的尺寸和/或形状分布。由上述两种方法得到的分布与透射电子显微镜(TEM)得到的分布的比较表明，SERS效应起始处的粒子或团簇的大小超过几个数量级。因此，SERS效应主要是由耦合在小于可见光区的小突起的等离子体本征模的共振引起的。©1998 John Wiley&Sons，Ltd.
This paper develops new approaches to characterize the morphology of silver and gold colloids used as substrates underlying surface-enhanced Raman scattering (SERS). Since both electromagnetic and chemical SERS theories predict that the Raman enhancement depends strongly on surface roughness features, a better understanding of the SERS spectra and an optimization of the enhancement factor require the knowledge of the size and shape distributions of the particles and clusters of the metal sols. For this purpose, we have investigated two in situ techniques. The first deals with the mechanical vibration band (also called acoustic mode) of the metallic particles of the colloidal sols; this band can be observed at very low Raman wavenumber shifts (approximately 10 cm-1) provide it is enhanced by surface plasmon resonance excitation. The experiments on these acoustic modes were carried out on silver and gold colloids, at several laser excitation wavelengths and in the presence of various polarizable molecules (pyridine, acridine, benzoic acid) or halide ions. Since the wavenumber and the shape of these acoustic bands are related to the morphology of the colloidal particles, a previously developed model was used which permits the calculation of the acoustic mode profiles, to approach the size and shape distributions of the roughness features giving rise to the SERS enhancement. Since extinction, scattering and absorption bands of metal colloids arise from surface plasmon resonance excitation, UV–visible spectroscopy is also a powerful tool for analyzing the optical properties of colloids. From the observed extinction profiles of silver and gold colloids, aggregated with the same probe molecules as those used in the low Raman wavenumber scattering experiments, attempts were made to obtain the size and/or the shape distributions of the various aggregates. The comparison between the distributions deduced from both of the above-mentioned methods along with those obtained by transmission electron microscopy (TEM) suggests that the particles or clusters at the origin of the SERS effect are sized over several orders of magnitude. It is therefore concluded that the SERS effect arises mainly from the resonance of plasmon eigenmodes of small protrusions coupled over regions smaller than the visible wavelength. © 1998 John Wiley & Sons, Ltd.