二维材料的电、磁性能调控及其微波吸收机制研究

In the field of electromagnetic wave absorbing materials, the wave absorbing performance of intrinsically non-magnetic nanomaterials is usually attributed to dielectric loss, and defect-induced static ferromagnetism as well as its effect on the dynamic magnetic losses is often neglected. Our group, for the first time, has found in previous researches that though bulk titanium nitride (TiN) is non-magnetic, nanostructure TiN can be endowed with weak static ferromagnetism through the manipulation of chemical composition and structural defect; and the as-obtained nanostructure TiN possesses a high dielectric loss towards electromagnetic wave as well as a high dynamic magnetic loss which does not match with the static ferromagnetism. In terms of the study of the electromagnetic wave transmission behavior and energy dissipation mechanism of nanomaterials, it needs to avoid the complexity of nanoparticles caused by their different composition and structure on the surface in comparison with those of the bulk counterparts. Therefore, graphene and h-BN, two kinds of two-dimensional materials with similar structure but considerably different electrical properties, are selected as the object of study in the present project. By manipulating the composition and structure of graphene and boron nitride through element doping and surface modification, this project is to endow the two kinds of materials with the electrical properties of conductor, semiconductor and insulator, as well as room temperature ferromagnetism with the assistance of structural design or defect inducing. Besides, the project is to investigate the structure-performance correlation among the chemical composition, structural defect and morphology of the two kinds of materials and their electrical properties, magnetism and electromagnetic wave absorbing performance. Furthermore, it is to elucidate the internal physical mechanisms that are responsible for the interactions between nanomaterials and electromagnetic waves, thereby providing a theoretical basis for and experimental guidance to the design and preparation of electromagnetic wave absorbing materials possessing excellent comprehensive properties.

在吸波材料领域，通常将非磁性纳米材料的吸波性能归因于其介电损耗，而忽略微观结构缺陷等诱导的静态铁磁性及其对动态磁损耗的影响。本课题组在前期研究工作中首次发现，通过调控纳米氮化钛的化学组成和结构缺陷，可使其具有弱静态铁磁性，同时表现出电磁波高介电损耗以及与静态铁磁性不匹配的高动态磁损耗。为了深入研究电磁波在纳米材料中的传输行为及损耗机制，避免因纳米颗粒表面和体相的组成和结构差异引起的问题复杂化，本项目拟以结构相似而电学性能迥异的石墨烯和六方氮化硼这两种二维材料作为研究对象；利用元素掺杂和表面改性等进行组成和结构调控，分别赋予其导体、半导体及绝缘体的电学性质，同时通过结构设计或缺陷诱导产生一定的室温铁磁性；研究其化学组成、结构缺陷、聚集形态等与电性能、磁性能及吸波性能之间的构效关系，阐明纳米材料与电磁波交互作用的内在物理机制；为设计、制备综合性能优异的电磁波吸收材料提供理论依据和实验指导。

本项目以结构相似而电学性能迥异的石墨烯和六方氮化硼（BN）这两种二维材料为研究对象，研究了不同组成、形态及宏观聚集结构等对RGO，BN阻抗匹配性能和电磁波耗散性能的影响。通过调控水热反应条件及反应体系，实现了RGO气凝胶孔道结构及石墨烯纳米片形态的调控。基于石墨烯纳米片大比表面积的优势，在添加量极低的条件下，复合材料即可表现出优异的介电损耗能力，从而实现了轻质高效吸波材料的设计制备。借助于原位复合制备得到系列不同种类石墨烯基复合材料，在提高RGO纳米片分散行为的同时，实现了不同种类特征异质界面的构筑。不同异质界面的引入不仅可以赋予材料更多的极化损耗机制及增强的有效介电损耗能力，同时也有利于实现材料的阻抗匹配性能优化及有效吸波频段范围的有效调控。进一步的，借助于异质元素掺杂也可以引入更多的缺陷位点和极化中心，赋予材料更多的高频极化损耗机制，实现RGO室温到高温范围吸波性能的优化。应用理论计算方法，建立单层RGO及氮原子掺杂模型，BN及O原子取代掺杂BN模型，从原子层面对掺杂态石墨烯和氮化硼局域晶体缺陷进行了深入分析。不同于纯相石墨烯，氮化硼电子密度的均匀周期性分布，掺杂后电荷分布不再平衡，有助于偶极子的形成，进而提升材料的介电性能。该项目研究了石墨烯，氮化硼化学组成、结构缺陷、聚集形态等与电性能、磁性能及吸波性能之间的构效关系，不仅有助于阐明二维材料与电磁波交互作用的内在物理机制，也为设计、制备轻质高效电磁波吸收材料提供理论依据和实验指导。