Sodium chloride (NaCl) films were grown on an Si(100)-(2 × 1) surface at near room temperature by molecular beam epitaxy (MBE). The atomic structure and growth mode of the prototypical ionic materials on the covalent bonded semiconductor surface is examined by synchrotron core-level x-ray photoemission spectrum (XPS), scanning tunneling microscopy (STM), and first-principles calculations. The Si 2p, Na 2p, and Cl 2p core-level spectra together indicate that adsorbed NaCl molecules at submonolayer coverage [i.e., below 0.4 monolayer (ML)] partially dissociate and form Si-Cl species, and that a significant portion of the dangling-bond characteristics of the clean surface remains after NaCl deposition of 1.8 MLs. The deposition of 0.65-ML NaCl forms a partially ordered adlayer, which includes NaCl networks, Si-Cl species, adsorbed Na species, and isolated dangling bonds. The STM results revealed that the first adlayer consists of bright protrusions which form small c(2 × 4) and (2 × 2) patches. Above 0.65 ML, the two-dimensional NaCl double-layer growth proceeds on top of the first adlayer.

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.

This work investigates the adsorption of diatomic interhalogens (XY = ICl and IBr) and hydrogen halides (HX = HBr and HCl) on Si(100) and Ge(100) surfaces by synchrotron radiation core-level photoemission and scanning tunneling microscopy (STM). It was found that mixed adsorbates (X and Y) or (H and X) each terminate a surface dangling bond while preserving the dimer structure. The coverage ratios of Cl/I and Br/I are slightly below the stoichiometric value of 1 for Si(100):ICl (the ICl-passivated Si(100) surface) and Si(100):IBr, respectively, but ∼1.4 for Ge(100):ICl. The X/H coverage ratios for HCl and Si(100):HBr are also less than 1. The mixed adsorbate system form well-ordered or partially ordered structures for chlorine-contained molecules on Si(100), but no adsorbate ordering is observed for bromide-contained molecules. In a sequel paper, we will present ab initio calculations for the energetics for the Si(100) surface with two mixed adsorbates to provide a more in-depth understanding of the experimental findings presented here.