Multiple Optical Excitation Pathways at Fe₃O₄/Ag(100) Interface Enabled by Metal-Induced Gap State

Optical excitation in bulk oxide semiconductors predominantly proceeds via band-edge transitions, generating hot carriers near the conduction-band minimum (CBM). However, populating high-lying unoccupied states above the CBM is often less efficient because of energy-momentum constraints and weak transition dipole moments. Here, using a prototypical metal/oxide junction consisting of monolayer Fe₃O₄ on Ag(100), we show that a metal-induced gap state (MIGS) created by strong interfacial hybridization serves as the dominant electronic reservoir for accessing high-lying unoccupied conduction bands (CBs) and image potential (IP) states near vacuum level. Beyond hot-electron population of the CBM, the MIGS provides efficient pathways for MIGS→CB and MIGS→IP transitions, whereas valence-band contributions are secondary. These excitations establish pronounced spatial charge separation across the Fe₃O₄/Ag(100) interface, in contrast to isolated oxides where gap states typically act as recombination centers. Our results highlight interfacial electronic-structure engineering as an effective strategy to generate energetic carriers for photocatalysis and optoelectronic applications.