Surface electronic structure of Ni-doped Fe3O4(001)

Magnetite $({\mathrm{Fe}}_{3}{\mathrm{O}}_{4})$ doped with earth-abundant metals has emerged as a promising catalyst material, with Ni-doped magnetite $(\mathrm{Ni}/{\mathrm{Fe}}_{3}{\mathrm{O}}_{4})$ being a cost-effective, durable, and highly active material for photocatalytic and electrochemical water oxidation. While previous studies have investigated the incorporation of Ni atoms into ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ single-crystalline surfaces using surface science characterization methods and density functional theory calculations, an experimental study is still required to understand the impact of Ni incorporation on the electronic structure of $\mathrm{Ni}/{\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ systems. To address this, we employed angle-resolved photoemission spectroscopy, analyzed within the one-step model of photoemission by a real-space multiple scattering code to investigate the electronic structure of the reconstructed magnetite surface. Moreover, the half-metal to semiconductor phase transition upon Ni incorporation is reflected in an almost complete disappearance of states near the Fermi level. Finally, we report on the systematic changes in the unoccupied states observed with the increasing amount of Ni dopant. These findings offer insights into the influence of Ni incorporation on the electronic structure of $\mathrm{Ni}/{\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$, which can link to an increased catalytic activity.