Co_3O_4纳米片的简单热氧化法制备及其磁性能

Simple Thermal Oxidation Synthesis and Magnetic Properties of Co_3O_4 Nanoflakes

在空气气氛下,通过简单的电热板将氧化沉积在硅基片上的钴薄膜在553~723 K下加热24 h,制备出了大面积Co3O4纳米片,并对纳米片的形貌、晶体结构、生长机制及其磁性能进行了系统研究。结果表明：Co3O4纳米片垂直基片生长,其厚度约为25~80 nm,长度可达1μm,纳米片尺寸随热氧化温度升高而增加。与相应的块体材料对比,Co3O4纳米片的Néel转变温度TN显著降低,约为20 K。450℃热氧化形成的样品5 K时的磁滞回线具有明显交换偏置,交换偏置场约为9.6×10-3T。Co膜简单热氧化生成Co3O4纳米片的过程分为两步：首先在Co膜表面由里往外形成了Co O层和Co3O4层,随后Co3O4纳米片在外层的Co3O4氧化层上形核生长,并最终形成了未氧化的Co层/Co O层/Co3O4层/Co3O4纳米片层的多层结构。这种较低温度下热氧化生成Co3O4纳米片的生长过程是一种短程扩散生长机制,并受钴离子的向外扩散速率控制,生成的纳米片的形状与Co3O4晶体结构密切相关。

Large-area CO3O4 nanoflakes were synthesized by heating the Co film oxidation deposited on silicon substrate in air at 553 ~ 723 ℃ for 24 h, using a very simple hotplate technique. The morphologies, crystal structures, growth mechanism and magnetic properties of tbe nanoflakes were investigated. The results showed that single-crystal CO3O4 nanoflakes grew perpendicularly to the sub- strate with a thickness of 25 ~ 80 nm and a width up to 1 μm. The sizes of the nanoflakes increased with the temperature increasing. The Neel temperature （TN） of CO3O4 nanostructures was about 20 K, which was much lower than that of its bulk counterpart. Also, there was an exchange bias field of 9.6×10 -3 T existed at 5 K. The process for CO3O4 nanostructures growth via simple thermal oxida- tion of Co film included two steps： Co and CO3O4 layers formed on the Co film firstly, then CO3O4 nanostructures grew above the upper CO3O4 layer. And the multi-layer structures, Co/CO3O4/CO3O4-nanoflakes formed finally. A diffusion mechanism was responsible for the Co3O4 nanoflakes growth at relatively low temperatures, which was controlled by the diffusion of cobalt ions. And the Co3O4 nanoflake morphologies were closely related with the Co3O4 crystal structure.