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

本文描述了用纯净的水溶液进行铁氧体电镀的方法，以减少杂质颗粒的形成，这些杂质颗粒被合并到镀膜中，并降低其微结构和磁性能。为了实现超净溶液，1)用超纯水配制了反应液和氧化液，并通过直径为0.1微米的膜过滤器提供；2)在反应过程中，用氨水代替CH3COONH4，以保持反应的pH值；CH3COONH4与Fe2+和Gt；在玻璃衬底或聚合物微球上制备了磁性铁氧体(Fe3O4)和镍锌铁氧体薄膜，并以包覆铁氧体的聚合物微球为载体进行了酶免疫分析。铁氧体涂层是利用磁场收集颗粒所必需的。铁氧体涂层的厚度要求等于或小于50 nm，才能在水中获得良好的分散性能。在没有使用清洁溶液技术的方法中，由于溶液中形成的掺杂杂质颗粒导致了约100 nm的大颗粒，因此无法获得如此厚度的连续薄膜。在新方法中，在初始阶段观察到10-20 nm的细小颗粒。当涂层厚度为50 nm时，聚合物粒子被铁氧体涂层完全包裹，表面光滑，由均匀细小的颗粒组成。穆斯堡尔谱表明，涂层由磁铁矿组成。饱和磁化强度与体积值基本相同。包覆了50 nm厚磁铁矿的颗粒在水中表现出良好的分散性能，在40Oe的磁场下具有良好的磁选效率。这些性能均优于市场上市场上的酶免疫分析产品。

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.