新型半导体型 MXenes 的合成及物性研究

Two dimensional transition metal carbides (MXenes) with graphene like structure were generally produced by selective of Al sublayer from corresponding ternary layered MAX phases in fluoride-containg solution. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, biosensors, and catalysis. However, it is very difficult to develop Sc, Y, Gd, and Lu –containing 2D carbides through this traditional method since the corresponding ternary MAX phases precursors are unable to form. To date, experimentally synthesized MXenes are all metallic, and it is still a great challenge to realize the synthesis of semiconducting or magnetic MXenes. This project is aimed to develop Sc and Y containg semiconductor-type two-dimensional carbide with novel chemical conposition and crystal structure. A green etching method is proposed through the structural design and synthesis of novel Al-C containing layered precursor with tunable sublayer property and weakened interfacial bonding. Combining with DFT-based calculations, the compositional, structural, and physical properties of the as obtained 2D carbides will be thoroughly investigated. The influence of valence electron structure, atomic lattice arrangement, and surface chemical states on the intrinsic physical properties would be revealed. We expect to provide a theoretical basis for materials chemistry and structural diversity of 2D transition metal carbides, and to expand their potential applications in the area of next generation of flexible transparent devices with excellent performance.

具有类石墨烯结构的二维过渡金属碳化物（MXenes）由含氟溶液中刻蚀层状MAX相中Al亚层而获得，其组成丰富、性质可调，在储能、电磁干扰屏蔽、复合材料、吸附及传感等领域极具应用前景。但过渡金属Sc、Y、Gd、Lu等难形成M-Al-C组分的MAX相，且与氟亲和性极强，无法通过传统方法获得相应MXenes。目前实验报道的MXenes均呈金属性，半导体型及磁性MXenes的合成仍是很大挑战。本课题将设计合成含Al-C亚层新型层状前驱体，可控调谐亚层物性并弱化亚层界面，发展不含氟绿色方法以合成具有新颖组成、结构及半导体性质的ScC、(Scx,Gd1-x)C、YC等二维碳化物，结合理论计算探索其结构、组成及物性，阐明不同过渡金属外层电子结构、原子尺度排布及表面官能团对其本征物性的作用机制，为拓展MXenes材料化学、结构多样性及在下一代柔性透明器件等领域的应用提供理论基础。

具有类石墨烯结构的二维过渡金属碳化物（MXenes）由含氟溶液中刻蚀层状MAX相中Al亚层而获得，其组成丰富、性质可调，在储能、电磁干扰屏蔽、复合材料、吸附及传感等领域极具应用前景。但过渡金属Sc、Y、Gd、Lu等难形成M-Al-C组分的MAX相，且与氟亲和性极强，无法通过传统方法获得相应MXenes。目前实验报道的MXenes均呈金属性，半导体型及磁性MXenes的合成仍是很大挑战。本项目设计合成了含Al-C亚层的新型层状前驱体ScAl3C3，发展了不含氟有机碱液绿色刻蚀方法，合成了具有新颖结构及组成的直接带隙半导体(2.5 eV)型Sc系二维材料ScCxOH,结合理论计算探索了其结构、组成及物性。以剥离态的几层结构ScCxOH片层制作了光探测器件，发现其在紫外可见光区域具有良好的光电响应性(0.125A/W，10V，360nm)及高量子效率，该工作为拓展MXenes材料化学、结构多样性及在下一代柔性透明器件等领域的应用提供了基础。申请人受到启发，进一步探索了全新硼系二维材料的合成，通过选择性刻蚀面内有序的四元层状硼化物Mo4/3Sc2/3AlB2 及 Mo4/3Y2/3AlB2的Sc/Y及Al元素，并通过进一步插层剥离，实现了首个单层二维硼化物Mo4/3B2-xTz (Tz = O, F, OH)的合成。在以上工作基础上，申请人进一步拓展探索了四元硼化物Ti4MoSiB2的绿色刻蚀，通过温和氯化锌熔盐中的选择性刻蚀，获得了具有4.1 eV带隙的二维半导体材料TiOxCly。此外，申请人将高熵概念引入到MAX相及MXene材料体系中，基于固相反应合成了Ti1.0V0.7Cr0.05Nb1.0Ta1.0AlC3 高熵MAX相，并通过选择性刻蚀合成了相应的二维高熵MXene, Ti1.1V0.7CrxNb1.0Ta0.6C3Tz (Tz = -F, -O, -OH), 并探索了其作为电容器电极材料的应用。