Characterization of laser-ablated and chemically reduced silver colloids in aqueous solution by UV/VIS spectroscopy and STM/SEM microscopy
Characterization of laser-ablated and chemically reduced silver colloids in aqueous solution by UV/VIS spectroscopy and STM/SEM microscopy
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DOI：
10.1007/s00340-002-1024-3
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发表时间：
2002-11-01
影响因子：
2.1
通讯作者：
Kleinermanns, K
中科院分区：
文献类型：
--
作者：
Brause, R;Möltgen, H;Kleinermanns, K
采用不同的扫描显微镜技术和UV/维斯光谱对水溶液中的银胶体进行了研究。银胶体是通过化学还原或纳秒激光烧蚀从水中的固体银箔产生的。激光功率和烧蚀时间的变化导致不同尺寸的金属团簇在水中的溶液。我们用紫外/维斯光谱表征了团簇的电子吸收。STM（扫描隧道显微镜）成像的金属胶体显示原子分辨率的棒或榫状银团簇的长度可达10 nm的激光烧蚀形成。然而，我们的扫描电子显微镜测量表明，也形成了大得多的银胶体，长度可达5-μ m，这是不可见的STM由于其粗糙度。我们将它们与多峰UV/维斯光谱的长波长尾部相关联。通过化学还原得到的银胶体通常较大，并且与激光烧蚀的团簇相比，它们的电子光谱发生红移。在532 nm和355 nm处用适当能量密度的纳秒激光脉冲照射胶体溶液最初减小胶体尺寸。然而，在355 nm下更长的照射导致再次形成更大的胶体。似乎有一个临界的较低的颗粒尺寸，其中银簇在水溶液中变得不稳定，并开始凝聚。
Silver colloids in aqueous solution were studied by different scanning microscopy techniques and UV/VIS spectroscopy. The silver colloids were produced either by chemical reduction or by nanosecond laser ablation from a solid silver foil in water. Variation of laser power and ablation time leads to solutions of metal clusters of different sizes in water. We characterized the electronic absorption of the clusters by UV/VIS spectroscopy. STM (scanning tunneling microscope) imaging of the metal colloids shows atomic resolution of rod- or tenon-like silver clusters up to 10-nm length formed by laser ablation. Our scanning electron microscope measurements, however, show that much larger silver colloids up to 5-mum length are also formed, which are not visible in the STM due to their roughness. We correlate them with the long-wavelength tail of the multimodal UV/VIS spectrum.. The silver colloids obtained by chemical reduction are generally larger and their electronic spectra are red-shifted compared to the laser-ablated clusters. Irradiation of the colloid solution with nanosecond laser pulses of appropriate fluence at 532 nm and 355 nm initially reduced the colloid size. Longer irradiation at 355 nm, however, leads to the formation of larger colloids again. There seems to be a critical lower particle size, where silver clusters in aqueous solution become unstable and start to-coagulate.