Nanoscale island manipulation and construction of heterojunctions by mechanical collision of 2D materials

Controllable phase transitions between distinct polymorphs in transition metal dichalcogenides (TMDs) hold great significance for applications in nanoscale electronics. Currently, constructing nanoscale heterojunctions with the desired TMD phase remains challenging due to insufficient control. In this study, we provided a new strategy of phase transitions by controllable mechanical collision of TMD islands containing over thousands of atoms. Using an <i>in situ</i> scanning tunneling microscopy (STM) tip manipulation technique, we can precisely control the fixed-axis rotation of nanoscale NbSe₂ islands. Through mechanically colliding T- and H-NbSe₂ with each other, we successfully triggered a phase transition from Mott insulator T-NbSe₂ to semi-metal H-NbSe₂, thereby creating a high-quality heterojunction. We further unveiled the unusual electronic properties of this heterojunction, and provided new insights into the phase transition mechanisms in TMDs and their potential applications in nanoscale electronics.