磁性共振氧化物纳米球设计与合成

Magnetic resonance is the prerequisite for electromagnetic metamaterials. Simultaneously, the interaction between magnetic and electric resonance can give rise to the directional transmission of electromagnetic waves at nanoscale. Unfortunately, there are no nature materials that can support magnetic resonances in optical region. The development of artificial magnetic materials has therefore attracted extensive research interest. To date, the artificial magnetic materials include circle-shaped noble metal nanostructures and high-refractive-index dielectric nanomaterials. However, noble metals have very high Ohmic loss in optical region, and high-refractive-index dielectric nanomaterials have difficulty in their controllable preparation. In this proposal, we intend to develop a new type of magnetic materials in optical region, which is based on facile synthesized metal oxide nanospheres. We will study magnetic resonance and directional scattering properties of the prepared metal oxide nanospheres as well as metamaterial properties based on the magnetic resonances of the metal oxide nanospheres. In our studies, the metal oxides that can have strong magnetic resonance in their nanospheres will first be identified by systematical theoretical calculations and simulations. The facile chemical methods will then be developed to prepare the identified metal oxide nanospheres with controlled size and shapes. The magnetic resonance and the directional scattering properties of the prepared nanospheres will be studied in single-particle level. The metamaterial properties of thin film composited with the metal oxide nanospheres will be further investigated. The success of this proposal can achieve non-metal, facile synthesized artificial magnetic materials in optical region, which paves the way for the development of metamaterials and nanoantenna in optical region.

人工光频磁性共振材料是实现电磁超材料和光学定向纳米天线的基础,引起了国内外研究者的广泛兴趣。针对金属人工光频磁性共振材料的高损耗和高折射率人工光频磁性共振材料合成困难等瓶颈问题，本项目首次提出采用中等折射率的氧化物，实现光频波段无损耗、易合成的人工磁性共振材料，并对其定向散射性质和在超材料中的应用进行研究。将通过理论计算和数值模拟的方法，确定出纳米球在光频波段具有优异磁性共振性质的氧化物，发展这些氧化物纳米球可控合成的湿化学方法。采用暗场散射技术,在单个颗粒尺度上对氧化物纳米球的磁共振性质和定向散射性进行系统地研究，最终设计出具有超级定向散射性质的光学纳米天线。同时，采用旋涂法或提拉法，制备氧化物纳米球的二氧化硅和高分子复合物薄膜，并对复合物薄膜的电磁超材料性质进行研究。本研究有望实现非金属、易合成的人工光频磁性共振纳米材料，为光频超材料和定向纳米光学天线的发展提供理论依据和技术积累。

本项目针对金属人工光频磁性共振材料的高损耗和高折射率人工光频磁性共振材料合成困难等瓶颈问题，首先采用米氏理论对球形介质纳米材料的电磁共振进行了系统地研究，揭示了介质纳米球的电磁共振对纳米球的介电函数和尺寸的依赖关系。随着介电函数和尺寸的增加，纳米球中的所有电磁共振模式均红移，但是每种模式的红移速率不一致。当纳米球的尺寸为200 nm时，折射率大于1.7时，介质纳米就可以在可见光波段产生明显的电磁共振；折射率在1.7~3.0时，介质纳米球的电偶极和磁偶极共振位置较近，在光谱上显示出一个散射峰；当折射率大于3.0是，电偶极和磁偶极共振位置相差较大，在光谱上形成两个散射峰。随后对介质纳米球的定向光散射性质进行了研究，结果表明介质纳米球的定向光散射性质依赖于电和磁共振模式的重叠程度和相对强度。当电和磁共振位置重叠且强度相当，介质纳米球就有优异的定向光散射性质。根据理论计算结果，筛选出折射率在1.7~3.0的氧化物半导体主要有Cu2O、Fe2O3和TiO2等。分别采用是化学法和超声喷雾法制备了Cu2O、Fe2O3和TiO2纳米结构，并对其电磁共振性质和定向光散射性质进行了研究。结果表明这三种材料的纳米结构均在光频波段具有强的电磁共振性质和良好的定向光学散射性质，实现了基于氧化物介质纳米结构的定向纳米天线和超材料。