Adsorbate-induced one-dimensional long-range modulation of an epitaxial insulator film

Using low-energy electron diffraction and scanning tunneling micrsocopy, we found that epitaxial NaCl films grown on Ge(100) with thicknesses up to (at least) 15 monolayers can be modulated with a period of six lattice constants and an amplitude directed mainly normal to their surface. The $\text{(6×1)}$ periodicity on the NaCl films is induced by a preadsorbed Na layer at very low coverages $\text{(Θ≈0.06),}$ that form chain structures with a sixfold periodicity in one dimension. At 10 monolayers thickness of NaCl a modulation amplitude of 0.28 Å was obtained.