Optical in Situ Study of InP(100) Surface Chemistry: Dissociative Adsorption of Water and Oxygen

Semiconductors designated for solar water-splitting need to be simultaneously stable and efficient in the charge transfer over the interface to the aqueous electrolyte. Although InP(100) has been employed as photocathode for several decades, no experimental data on its initial interaction with water is available. We study reaction mechanisms of well-defined surfaces with water and oxygen employing photoelectron and in situ reflection anisotropy spectroscopy. Our findings show that reaction path and stability differ significantly with atomic surface reconstruction. While the mixed-dimer In-rich surface exhibits dissociative water adsorption featuring In-O-P rather than unfavorable In-O-In bond topologies, the H-terminated, P-rich surface reconstruction is irreversibly removed. Oxygen exposure attacks the In-rich surface more efficiently and additionally modifies, unlike water exposure, bulk-related optical transitions. Hydroxyl is not observed, which suggests a dehydrogenation of adsorbed species already at ambient temperature. Our findings may benefit the design of InP(100) surfaces for photo-electrochemical water splitting.