The rise and fall of an oxide: insights into the phase diagram of bismuth oxide on Au(111)

Bismuth oxide (Bi${}_2$O${}_3$) is a polymorphic material of considerable technological interest, with applications spanning from heterogeneous catalysis to next-generation nanoelectronics. Despite its relevance, systematic investigations of Bi${}_2$O${}_3$ thin films remain scarce. Here, we report a comprehensive, multi-technique study of bismuth oxide grown on Au(111). By combining synchrotron-based x-ray photoelectron spectroscopy and diffraction with low-energy electron diffraction and scanning tunneling microscopy, we elucidate the structural evolution of the surface during controlled oxidation and subsequent annealing. We find that Bi deposition induces well-defined surface reconstructions, whereas oxidation triggers the formation of a complex sequence of Bi${}_2$O${}_3$ domains. High-resolution spectroscopic and diffraction data enable us to propose a structural model consistent with the $(201)$ surface of $\beta$-Bi${}_2$O${}_3$. In addition, work function measurements reveal substantial electronic modifications at the interface. These results provide benchmark structural and electronic insights into the Bi oxide/Au(111) system and establish a framework for integrating Bi${}_2$O${}_3$ in devices in combination to two-dimensional semiconductors exploiting its low contact resistance.