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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。
In the air atmosphere, cobalt films oxidized and deposited on the silicon substrate were heated at 553 ~ 723 K for 24 h by a simple hot plate to prepare a large area of Co3O4 nanosheets. The morphology, crystal structure, Growth mechanism and magnetic properties of a systematic study. The results showed that the vertical growth of Co3O4 nanosheets with the thickness of 25-80 nm and the length of up to 1 μm increased with the increase of thermal oxidation temperature. Compared with the corresponding bulk materials, the Néel transformation temperature TN of Co3O4 nanosheets decreased significantly, about 20K. The hysteresis loop at 5 K formed by thermal oxidation at 450 ℃ has obvious exchange bias and the exchange bias field is about 9.6 × 10-3T. The process of simple Co-thermal oxidation of Co to Co3O4 nanosheets is divided into two steps: firstly CoO layer and Co3O4 layer are formed from the inside to the outside of Co film, and then the Co3O4 nanosheets nucleate and grow on the Co3O4 oxide layer of the outer layer and finally A multi-layered structure of unoxidized Co layer / CoO layer / Co3O4 layer / Co3O4 nanosheet layer was formed. The growth of Co3O4 nanosheets at lower temperatures is a kind of short-range diffusion growth mechanism controlled by the outward diffusion rate of cobalt ions. The shape of the resulting nanosheets is closely related to the crystal structure of Co3O4.