Stepped NaCl films grown epitaxially on Si-precovered vicinal Ge(100)

Low energy electron diffraction (LEED) and programmed thermal desorption sp ectroscopy (TDS) techniques have been used to characterize the morphology a nd modifications of the desorption kinetics of stepped NaCl(100) films whic h have been grown epitaxially on the vicinal Ge(100) surfaces with misorien tations up to 5.4 degrees in [011] direction. Even at this high misorientat ion the Ge surface contains about 60% steps of monoatomic height. The numbe r D-B of steps with double atomic height, however, can be significantly inc reased by adsorption of 0.5 ML Si at 470 K. At room temperature NaCl grows as a rough him with non-polar NaCl steps along the [010] and [001] directio ns, respectively. Growth of NaCl films at surface temperatures at or below 200 K, however, produces polar steps which most likely consist of pairs of alternating Na+ and Cl- terminated steps. No significant influence on the e lectronic structure by either type of step could be detected with ultraviol et photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). Adsorbed species like water and CO, do not dissociate on the stepped NaCl surfaces, but are bound more strongly than on flat surfaces. For CO, the non-polar NaCl steps produced a new desorption peak located at 115 K corresponding to a desorption energy of 38 kJ/mol, close to that found for adsorption at F centers (40 kJ/mol). (C) 2000 Elsevier Science B.V. All rights reserved.