用化学镀法制备 Pd/Ag 膜时膜厚和组成的控制

 研究了不同 Pd2+含量的镀液在多孔陶瓷载体上的化学沉积规律, 发现当 Pd 沉积层厚度达到约 5 μm 后, 即使镀液中反应物的消耗比例很小, 膜厚增长也明显变缓, 沉积反应主要受膜层表面的催化活性位控制; 当镀液中 Pd2+含量只能沉积形成小于 4 μm 的 Pd 膜时, 在 323 K 化学镀 180 min 后, 镀液中 Pd2+的转化率高于 90%. 与之相似, 当 Ag 镀液中的 Ag+含量等于 0.5~2 μm 的 Ag 膜层所需量时, 在 333 K 化学镀 120 min 后, Ag+的转化率可达 95%. Ag+的高转化率与 Ag 颗粒的择向生长特性有关. 根据 Pd 和 Ag 的化学镀沉积规律, 通过调节镀液中金属离子的含量能够预先设计和精确控制超薄 Pd/Ag 膜的膜厚和组成.

Control of Thickness and Composition of Pd/Ag Membrane during Layer-by-Layer Electroless Plating

The deposition rules of Pd were investigated during electroless plating in baths with different amounts of Pd²⁺. It was demonstrated that the Pd deposition rate was controlled by the auto-catalytic activity of the metal layer surface when the deposited Pd layer became thicker than 5 μm even if Pd²⁺ in the plating baths was far from being consumed. When the Pd²⁺ amount in the bath was kept lower than that necessary for reaching the Pd layer thickness (e.g. corresponding to 1–4 μm Pd), the Pd²⁺ conversion in the bath was higher than 90% after reaction for 180 min. Furthermore, the same was found during Ag deposition from silver plating baths with a low amount of Ag⁺, i.e. Ag⁺ conversion was higher than 95% after plating for 120 min in baths containing Ag⁺ sufficient for thick Ag layer of 0.5–2 μm. It was proved by scanning electron microscopy measurements that the higher conversions of Ag⁺ were related to the special growth properties of Ag particles. According to the deposition rules of Pd and Ag, the thickness and metal composition of ultra-thin Pd/Ag membranes prepared by layer-by-layer electroless plating could be pre-designed as well as accurately controlled by preparing relevant plating bath with low amounts of metal.