Theoretical analysis of the electronic structure of the stable and metastable c(2x2) phases of Na on Al(001): Comparison with angle-resolved ultra-violet photoemission spectra

Using Kohn-Sham wave functions and their energy levels obtained by density-functional-theory total-energy calculations, the electronic structure of the two c(2x2) phases of Na on Al(001) are analysed; namely, the metastable hollow-site structure formed when adsorption takes place at low temperature, and the stable substitutional structure appearing when the substrate is heated thereafter above ca. 180K or when adsorption takes place at room temperature from the beginning. The experimentally obtained two-dimensional band structures of the surface states or resonances are well reproduced by the calculations. With the help of charge density maps it is found that in both phases, two pronounced bands appear as the result of a characteristic coupling between the valence-state band of a free c(2x2)-Na monolayer and the surface-state/resonance band of the Al surfaces; that is, the clean (001) surface for the metastable phase and the unstable, reconstructed "vacancy" structure for the stable phase. The higher-lying band, being Na-derived, remains metallic for the unstable phase, whereas it lies completely above the Fermi level for the stable phase, leading to the formation of a surface-state/resonance band-structure resembling the bulk band-structure of an ionic crystal.Comment: 11 pages, 11 postscript figures, published in Phys. Rev. B 57, 15251 (1998). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Untersuchungen zur Abwassereinleitung: Statistik wichtiger industrieller und gewerblicher Branchen zur Bewertung der Umweltgefaehrlichkeit von Stoffen

In this project for the German Federal Environmental Agency new statistical values for wastewater and production were ascertained. A comprehensive questionnaire was sent to companies in the branches of paper making, textile finishing and leather production. These values are used to check standard figures in the EU for risk assessment of substances in the aquatic compartment, e.g. the volume flows through sewage works or the dilution factors of receiving water. A return between 60-78%, depending on the branch, was achieved. This high rate of return was due to the careful preparation of the questionnaires, support from the associations and persistent enquiries. Different values were collected in order to be able to apply all the different methods of chemical evaluation. The values were analysed against the number of bussinesses and, for the purpose of comparison only, against the production and wastewater quantities. These analyses were carried out in consultion with the project sponsor. The volume flows of the industrial sewage works of the facilities in all three branches which discharge their wastewater directly to the receiving waters were determined. The 10 percentile score of these facilities amounted to only to a quarter of the EU standard figure of 2,000 m"3/d. The analyses of the entire branch in each case yield dilution factors of 20-70% of the EU standard value of 10. Only the full tanning leather companies yielded a dilution factor of 10. The volume flows of the sewage treatment plants of the facilities discharging to the sewer system exceeds 2000 m"3/d in all cases. (orig.)SIGLEAvailable from TIB Hannover: RN 8908(98-018) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekUmweltbundesamt, Berlin (Germany); Bundesministerium fuer Umwelt, Naturschutz und Reaktorsicherheit, Bonn (Germany)DEGerman