Wang Xiaolong, Santschi Christian, Martin Olivier J F
Nanophotonics and Metrology Laboratory, Swiss Federal Institute of Technology (EPFL), CH-1015, Lausanne, Switzerland.
Small. 2017 Jul;13(28). doi: 10.1002/smll.201700044. Epub 2017 May 24.
Silver (Ag) nanostructures and thin films are advantageous plasmonic materials as they have significantly lower losses than gold (Au). Unfortunately, Ag nanostructures suffer from poor chemical and thermal stability, which limit their applications. Here, the mechanisms leading to the deterioration of Ag nanostructures are clarified. It is first shown that oxygen alone cannot oxidize Ag nanostructures. Then, experiments using X-ray photoelectron spectroscopy reveal that the amount of sulfur in ambient air is too low for efficient tarnishing of the Ag surface. Finally, water is found to be the most critical factor for the degradation of Ag nanostructures and thin films. At high relative humidity, adsorbed water forms a thin film enabling the migration of Ag ions at the Ag/air interface, which deteriorates the Ag nanostructures. A dehydration treatment is developed which alters the morphology of the deposited silver, leading to an improved chemical and thermal stability of the Ag nanostructures and films, which then remain stable for more than 14 weeks under ambient laboratory conditions. In addition, dehydration also improves significantly the root-mean-square roughness for Ag thin films deposited on a glass substrate.
银（Ag）纳米结构和薄膜是具有优势的等离子体材料，因为它们的损耗比金（Au）低得多。不幸的是，Ag纳米结构的化学和热稳定性较差，这限制了它们的应用。在此，阐明了导致Ag纳米结构劣化的机制。首先表明，仅氧气不能氧化Ag纳米结构。然后，使用X射线光电子能谱的实验表明，环境空气中的硫含量过低，无法有效使Ag表面变暗。最后，发现水是Ag纳米结构和薄膜降解的最关键因素。在高相对湿度下，吸附的水形成一层薄膜，使Ag离子在Ag/空气界面迁移，从而使Ag纳米结构劣化。开发了一种脱水处理方法，该方法改变了沉积银的形态，提高了Ag纳米结构和薄膜的化学和热稳定性，在实验室环境条件下，它们可保持稳定超过14周。此外，脱水还显著改善了沉积在玻璃基板上的Ag薄膜的均方根粗糙度。
