Electronic reconstruction at a buried ionic-covalent interface driven by surface reactions

Lattice-matched ionic NaCl films were grown layer by layer on covalent Ge 100 using cycles of two half reactions HRs that involved the alternative adsorption of Cl and Na. The Ge 3d photoemission spectra obtained after full cycles of growth resembled that of clean Ge 100 , 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 1.7 eV between these two interface configurations. Our results demonstrate that reactions on the NaCl surface drive periodic electronic reconstructions at the NaCl-Ge interface.