Metal-insulator transition in crystalline V$_2$O$_3$ thin films probed at atomic-scale using emission Mössbauer spectroscopy

Microscopic understanding the metal-to-insulator transition (MIT) in strongly correlated materials is critical to the design and control of modern “beyond silicon” Mott nanodevices. In this work, the local MIT behaviors in single crystalline V$_2$O$_3$ thin films were probed on an atomic scale by online $^{57}$Fe emission Mössbauer spectroscopy (eMS) following dilute ($<10^{-3}$ at.%) implantation of $^{57}$Mn$^+$ (T$_{1/2}$ = 90 s). Both the epitaxial and the textured V$_2$O$_3$ thin films grown by direct current magnetron sputtering were studied. Three structural components were resolved and identified in the eMS spectra with parameters characteristic of Fe in the 2+ valence state, which are attributable to Fe in either lattice damage or structural defects and Fe in the intrinsic crystal structure of V$_2$O$_3$, respectively. The results prove that the oxygen vacancies are common in the V$_2$O$_3$ thin films. With co-existence of both the non-stoichiometry and epitaxial strain in the thin films, the epitaxial strain plays a dominant role in controlling the global MIT properties of the film. The atomic scale structural transition captured by the eMS affirms the early-stage dynamics of the MIT of V$_2$O$_3$ thin film reported previously. These results approve the feasibility to tune the electronic transport of the V$_2$O$_3$ thin films for the next-generation Mott nanodevices by the epitaxial strain via the sample growth parameters.