Zou S, Weaver M J
Dept of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393.
Anal Chem. 1998 Jun 1;70(11):2387-95. doi: 10.1021/ac9800154.
Procedures are outlined for the electrodeposition of ultrathin films of Pt-group transition metals onto gold that provide intense surface-enhanced Raman scattering (SERS) for adsorbates bound to the overlayers yet (unlike earlier reports) are sufficiently "pinhole-free" to avoid significant spectral and chemical interferences from the underlying substrate. Constant-current electrodeposition of Pd, Rh, Pt, and Ir from perchloric acid and/or phosphate electrolytes yields essentially layer-by-layer growth, so that near-ideal pinhole-free electrochemical and spectral characteristics are achieved for film thickness of ∼2 monolayers or more. The desired film uniformity is diagnosed from the voltammetric oxide formation-removal behavior and, especially, from the absence of the characteristic C-O stretching (ν(CO)) SERS band at 2110-2120 cm(-)(1) due to CO binding to Au surface sites. Carbon monoxide is also employed as a surface environment-sensitive adsorbate to probe the electrochemical SERS characteristics as a function of the transition-metal film thickness. The Raman enhancement was observed to decrease by 2-fold every 10-20 Å or so, exhibiting a "spacer distance" dependence that is weaker than (but functionally similar to) recently reported organic insulator films. The practical value of the present films for obtaining rich vibrational spectra for diverse adsorbates on transition metals is pointed out and briefly illustrated for benzonitrile on a Pt film electrode. The more general promise of this overlayer film SERS strategy as a versatile vibrational technique for characterizing other types of chemically important surface materials is also noted.
本文概述了将铂族过渡金属超薄膜电沉积到金表面的方法，该方法可为吸附在覆盖层上的吸附质提供强烈的表面增强拉曼散射（SERS），而且（与早期报道不同）具有足够的“无针孔”特性，以避免来自底层基底的显著光谱和化学干扰。从高氯酸和/或磷酸盐电解质中恒电流电沉积钯、铑、铂和铱，可实现基本上逐层生长，因此对于约2个单层或更厚的膜厚度，可实现近乎理想的无针孔电化学和光谱特性。通过伏安法氧化形成-去除行为，尤其是通过不存在由于一氧化碳与金表面位点结合而在2110 - 2120 cm⁻¹处出现的特征性C - O伸缩（ν(CO)）SERS带，来诊断所需的膜均匀性。一氧化碳也被用作对表面环境敏感的吸附质，以探测作为过渡金属膜厚度函数的电化学SERS特性。观察到拉曼增强每10 - 20 Å左右下降2倍，呈现出“间隔距离”依赖性，这种依赖性比最近报道的有机绝缘膜弱（但功能相似）。指出了本研究薄膜对于获得过渡金属上各种吸附质丰富振动光谱的实际价值，并以苯甲腈在铂膜电极上为例进行了简要说明。还提到了这种覆盖层薄膜SERS策略作为一种用于表征其他类型化学重要表面材料的通用振动技术的更广泛前景。
