Cross-Sectional Observing Bias-Induced Phase Transformation of Multilayer TiSe2 Devices via In Situ Transmission Electron Microscopy

Over the past few decades, two dimensional transition metal dichalcogenides (TMDs) have attracted much attention due to their promising applications in electronics, optoelectronics, and catalysis. Titanium diselenide (TiSe₂), a notable member of the Group IV TMDs family, has attracted significant attention in both bulk form and its emerging two-dimensional form due to its interesting physical properties, such as charge density waves (CDW) and unconventional superconductivity. In this research, the device behaviors of TiSe₂ cross-sectional samples are revealed <i>via</i> in-situ biasing experiments and recorded by transmission electron microscope (TEM). Furthermore, we measured the <i>ex-situ </i>current-voltage curve as temperature changed and demonstrated the presence of titanium-rich regions on the surface of multilayer 2H-TiSe₂ in both<i> ex-situ</i> measurements and<i> in-situ </i>induced biasing using atomically resolved scanning transmission electron microscopy (STEM). During bias-induced phase changes, we also observed extreme current changes during applied voltage bias. In addition, we discussed how different thicknesses of 2H-TiSe₂ affect the maximum current value, noting that as the thickness increases, the voltage required for the phase change also increases. Herein, the electronic structure of the titanium-rich surface produced after biasing was probed by electron energy loss spectroscopy (EELS). It can be clearly seen that the valence states of both Ti and Se elements have changed significantly. This study clarifies the detailed mechanism behind the phase transformation process and explores the structural and electrical properties of Group IV TMDs. Furthermore, it highlights their additional application value and establishes a groundwork for future developments in this field.