Lattice-matched ionic NaCl films were grown layer by layer on covalent Ge͑100͒ using cycles of two half reactions ͑HRs͒ that involved the alternative adsorption of Cl and Na. The Ge 3d photoemission spectra obtained after full cycles of growth resembled that of clean Ge͑100͒, but came to resemble that of the polar Cl-terminated surface after the subsequent half reaction of Cl adsorption. Concurrently, the Na and Cl core levels of the nanofilms shifted by ϳ1.7 eV between these two interface configurations. Our results demonstrate that reactions on the NaCl surface drive periodic electronic reconstructions at the NaCl-Ge interface.

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Solar-induced photothermal catalytic H2O splitting is a promising method for H2 production. On metal oxides, the interaction between H2O and the surface can lead to the formation of oxygen vacancies (VOs) and alter the reaction pathway for overall H2O splitting. Herein, the free energy profiles of two different pathways on the In2O3 (110) surface are calculated based on density functional theory, and the relation between surface VO formation and the reactivity of surface VOs reveals that surface VOs with a lower formation energy are more unfavorable for H2 evolution. Doping In2O3 with a transition metal can effectively enhance the electron transfer from the surface O atoms to the doped metal, benefitting the formation of surface VOs and causing the doped metal to become the active reaction center for H2O splitting.