In recent years, TMDs have extensive application prospects in the fields of nanoelectronic devices, optoelectronic devices, energy and catalysis due to their unique structure and novel physical properties. However, the structural evolution mechanism of TMDs materials has hardly been explored. 

In this work, the scanning transmission electron microscopy (STEM) was used to study the structural evolution in PtSe2 and MoS2. By performing in situ experiments in an atomic resolution STEM, it is found that 2H  1T and 2H  N phase transition can be observed in bilayer PtSe2 under electron beam irradiation. The phase transition can be tracked in real time which enables in-depth analysis the transformation mechanism. The stacking sequences and twist angle in bilayer PtSe2 was also fully investigated by atomic resolution in situ STEM. The results show the diverse and dynamic features of bilayer PtSe2 structures which can be observed and directly tuned under electron beam illumination. This work revealed the phase transition and interlayer structure transition mechanisms of PtSe2 at atomic scale, which may have guiding significance for the use of structural engineering to control the performance of PtSe2. In addition, the structural transformation and stability of 1T'-MoS2 were studied. Moreover, the microstructure of MoS2 wrinkles and its effects on electrical properties were studied, which is helpful to understand the properties of MoS2 nanostructures and is of great significance to the structural design in the electronic field.

Dr Junjie Qi is the full Professor of University of Science & Technology Beijing, China. She received her Ph.D. degree from Department of Materials Science at University of Science & Technology Beijing in 2002. From Jan. 2003 to Dec. 2004, she had been with the Tsinghua University, where she was a Post-Doctoral researcher. She joined the Device Research Laboratory in Electrical Engineering Department at University of California, Los Angeles as a visiting scholar through Dec. 2013 to Dec. 2014. She is the author of more than 150 publications including “Nature Communications”, “Advanced Materials”. Her current research interests include semiconductor nanomaterials, electronic and opto-electronic properties and devices of low-dimensional materials.