中文摘要：

用Nd∶YAG脉冲激光器1064nm激发光在二次去离子水中制备了Pd胶体。此体系中Pd颗粒表面不存在杂质离子,为“化学纯净”。刻蚀后将Pd胶体沉积在铝基底上形成一层Pd岛膜。紫外-可见吸收光谱表明Pd胶体在200～800nm测量范围内没有出现特征吸收峰,说明Pd胶体的吸收光谱并不能反映Pd胶体中Pd颗粒的粒径分布等信息。SEM显示Pd岛膜由Pd纳米颗粒组成,其平均粒径在200nm左右。以10^-3mol·L^-1的4-巯基吡啶（4MPY）为探针分子对Pd胶体和Pd岛膜的表面增强拉曼散射（SERS）进行了研究。结果显示,在Pd胶体中没有获得4MPY的SERS信号;Pd岛膜是一种非常高效的活性增强基底,从实验数据估算得出其增强因子约为8.7×10^4。SERS光谱分析显示4MPY分子通过S原子以倾斜的方式吸附于Pd岛膜表面;与Pd岛膜表面相比,4MPY分子在Ag岛膜上更趋于采用垂直于表面的吸附取向。

英文摘要：

Palladium colloid was obtained via laser ablation under 1 064 nm excitation from an Nd∶YAG laser in redistilled deionized water. The Pd colloid consisted of ＂chemically pure＂ Pd nanoparticles, which were free from extraneous ions or other chemicals since no chemical reaction was involved in the preparation. There was no characteristic peak in UV/Vis spectrum of Pd colloid in the region of 200-800 nm. Hence, in contrast to the Au and Ag nanoparticles, the average size and the size distribution of the Pd nanoparticles could not be estimated from their UV/Vis adsorption spectral features. After the laser ablation, one drop （50 μL） of Pd colloid was deposited on the aluminum plate and dried naturally to form the Pd island films. This method resulted in the formation of a rough surface with a large number of separated Pd islands 20 μm in diameter. According to the SEM measurement, Pd nanoparticles with the average diameter of ～200 nm formed Pd island films. Surface-enhanced Raman scattering （SERS） activity of Pd colloid and Pd island films was evaluated by using 4-mercaptopyridine （4MPY） as a probe molecule. The SERS study revealed that Pd island film was a highly efficient SERS-active substrate while there was no SERS signal observed from Pd colloid. The surface enhancement factor of Pd island films for 4MPY was estimated, which could reach values as high as 8.7×10^4 under 632.8 nm excitation. This value was comparable with the largest value of 10^4 cited in the literature. The SERS spectra of 4MPY molecules adsorbed on Pd surface showed that 4MPY molecules probably tilted from the Pd nanoparticle surface-via sulphur. By contrast, SERS spectrum of 4MPY adsorbed on Ag island films was recorded and analysed. From SERS data it was inferred that 4MPY molecules assumed the standing up orientation on the silver nanoparticle surface. It could be concluded that the 4MPY molecules were more perpendicular to the silver nanoparticle surface than to the Pd nanoparticle surface.