Preparation of oxide thim films by ultra-clean ferrite plating and their magnetic properties

本报告描述了用纯净的水溶液压缩铁氧体电镀形成的杂质颗粒，这些杂质颗粒被纳入电镀膜中并降低其微观结构和磁性能。为了实现超净溶液，1)用超纯水制备反应溶液和氧化溶液，并通过孔径为0.1 μ m的膜过滤器供应；2)用氨溶液代替反应过程中的CH_3COONH_4，以保持pH值，而CH_3COONH_4与Fe^<2+>离子混合形成杂质颗粒。在玻璃衬底或聚合物球上合成了磁铁矿（Fe_3O_4）和镍锌铁氧体薄膜。采用铁氧体包覆的聚合物微球作为酶免疫分析的载体颗粒。铁氧体涂层是利用磁场收集颗粒所必需的。为了在水中获得良好的分散性能，要求铁氧体涂层的厚度等于或小于50nm。在不使用清洁溶液技术的方法中，由于在溶液中形成的杂质颗粒掺入导致的100 nm左右的大颗粒，因此无法获得这种厚度的连续薄膜。在新方法中，在初始阶段观察到10-20 nm的小颗粒。当层厚为50 nm时，聚合物颗粒被铁氧体涂层完全包裹，表面光滑，颗粒均匀细小。穆斯堡尔谱显示涂层由磁铁矿组成。饱和磁化强度与体积值基本一致。50 nm厚的磁铁矿包覆颗粒在水中表现出优异的分散性能和40 Oe磁场下的磁选效率。这些性能优于市场上的酶免疫测定产品。

This report describes the ferrite plating using purified clean aqueous solutions to compress the formation of impurity particles, which are incorporated in plated films and degrade their microstructure and magnetic properties. To realize the ultra-clean solutions, 1) a reaction solution and an oxidizing one were prepared using ultrapure water and supplied through membrane filters of 0.1 mum in pore diameter, 2) an ammonia solution was supplied to keep a pH value during the reaction instead of CH_3COONH_4 that forms impurity particles by mixing with Fe^<2+> ions. Magnetite (Fe_3O_4) and Ni-Zn ferrite films were synthesized on glass substrates or polymer spheres.The polymer microspheres with ferrite coatings are used as carrier particles for enzyme immunoassay. The ferrite coatings are necessary for collecting the particles using magnetic field. Thickness of the ferrite coatings is required to be equal or less than 50 nm to obtain a good dispersion performance in water. In methods without using the clean solution technique, continuous films with such thickness were not obtained due to large grains of around 100 nm, which were caused by incorporated impurity particles formed in the solution. In the new method, small grains of 10-20 nm were observed in the initial stage. When the layer thickness was 50 nm, the polymer particles were fully encapsulated with ferrite coatings, which have smooth surface and were composed of uniform and small grains. Mossbauer spectra showed that the coatings are composed of magnetite. The saturation magnetization was almost the same as the bulk value. The particles coated with 50 nm-thick magnetite exhibited the excellent dispersion performance in water and efficiency of magnetic separation by the magnetic field of 40 Oe. These performances were superior to those of the product in the market for enzyme immunoassay.