Real-Space Observation of an In Situ-Built Schottky Junction in a Two-Dimensional MXene Layer

Two-dimensional (2D) Ti 3 C 2 MXene-based metal has attracted much attention due to its capability of in situ-built Schottky junctions via oxidization of Ti and the formation of TiO 2 on the MXene surface. The real space observation of such a junction has not yet been explored to precisely understand the growth mechanism. In this study, direct observation of the evolution of electronic structures across 2D metal–semiconductor interfaces has been revealed in the in situ-grown Ti 3 C 2 –TiO 2 system using scanning tunneling microscopy (STM) and conductive atomic force microscopy (CAFM). From scanning tunneling spectroscopy (STS) and correspondingly the density of states (DOS) spectra, we mapped band edges across the differently time-aged layers in the air and at room temperature. Moreover, the band mapping across the oxidized layer reveals a Schottky-type band structure in the layer adjacent to the interface. Schottky junction formation was further confirmed by current–voltage characteristics and conductance mapping across the junction through CAFM. This study demonstrates the direct visualization of interfacial band mapping across the in situ-built 2D metal–semiconductor junction.