Thermally induced structural transformation of 2D materials opens unique avenues for generating other 2D materials by physical methods. Imaging these transitions in real time provides insight into synthesis routes and property tuning. We have used in situ transmission electron microscopy (TEM) to follow thermally induced structural transformations in layered CoSe₂. Three transformation processes are observed: orthorhombic to cubic-CoSe₂, cubic-CoSe₂ to hexagonal-CoSe, and hexagonal to tetragonal-CoSe. In particular, the unit-cell-thick orthorhombic structure of CoSe₂ transforms into cubic-CoSe₂ via rearrangement of lattice atoms. Cubic-CoSe₂ transforms to hexagonal-CoSe at elevated temperatures through the removal of chalcogen atoms. All nanosheets transform to basal-plane-oriented hexagonal 2D CoSe. Finally, the hexagonal to tetragonal transformation in CoSe is a rapid process wherein the layered morphology of hexagonal-CoSe is broken and islands of tetragonal-CoSe are formed. Our results provide nanoscopic insights into the transformation processes of 2D CoSe₂ which can be used to generate these intriguing 2D materials and to tune their properties by modifying their structures for electro-catalytic and electronic applications.

2D材料的热诱导结构转变为通过物理方法生成其他2D材料开辟了独特的途径。实时对这些过渡进行成像，可以深入了解合成路线和特性调整。我们已经使用原位透射电子显微镜（TEM）来跟踪分层CoSe _2中的热诱导结构转变。观察到三种转化过程：正交晶体到立方CoSe ₂，立方晶体CoSe ₂到六方CoSe，以及六方晶体到四方CoSe。特别地，COSE的晶胞厚的正交结构₂变换成立方COSE ₂经由晶格中的原子的重新排列。立方CoSe ₂通过去除硫属元素原子在高温下转变为六方CoSe。所有纳米片都转变为面向基面的六边形二维CoSe。最后，在CoSe中从六角形到四角形的转变是一个快速过程，其中六角形CoSe的分层形态被破坏，并形成了四角形CoSe的岛。我们的结果为2D CoSe ₂的转化过程提供了纳米的见解，可用于生成这些引人入胜的2D材料并通过修改其结构以用于电催化和电子应用来调整其性能。