Research progress of two-dimensional transition metal dichalcogenide phase transition methods

Following traditional semiconductors such as silicon and GaAs, in recent years the two-dimensional materials have attracted attention in the field of optoelectronic devices, thermoelectric devices and energy storage and conversion due to their many peculiar properties. However, the normal two-dimensional materials such as graphene, cannot be well used in the field of optoelectronics due to the lack of a band gap, and the black phosphorus is also greatly limited in practical applications due to its instability in the air. The two-dimensional transition metal dichalcogenides have attracted more attention due to the different atomic structures, adjustable energy band and excellent photoelectric properties. There are different crystal phases in transition metal dichalcogenides, some of which are stable in the ground state, and others are instable. Different phases exhibit different characteristics, some of which have semiconductor properties and others have like metal in property. These stable and metastable phases of transition metal dichalcogenides can be transformed into each other under some conditions. In order to obtain these metastable phases, thereby modulating their photoelectric performance and improving the mobility of the devices, it is essential to obtain a phase transition method that enables the crystal phase transition of the transition metal dichalcogenides. In this article, first of all, we summarize the different crystal structures of transition metal dichalcogenides and their electrical, mechanical, and optical properties. Next, the eight phase transition methods of transition metal dichalcogenides are listed, these being chemical vapor deposition, doping, ion intercalation, strain, high temperature thermal treatment, laser inducing, plasma treatment, and electric field inducing. After that, the research progress of these phase transition methods and their advantages and disadvantages are introduced. Finally, we sum up all the phase transition methods mentioned in this article and then list some of the problems that have not been solved so far. This review elaborates all of the presently existing different phase transition methods of transition metal dichalcogenides in detail, which provides a good reference for studying the phase transition of transition metal dichalcogenides in the future, the electrical performance regulated by different phases, and the applications of memory devices and electrode manufacturing.