Berlin 2005 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
O: Oberflächenphysik
O 36: Postersitzung (Elektronische Struktur, Grenzfl
äche fest-flüssig, Halbleiteroberfl
ächen und -grenzfl
ächen, Nanostrukturen, Oberfl
ächenreaktionen, Teilchen und Cluster, Struktur und Dynamik reiner Oberfl
ächen)
O 36.3: Poster
Montag, 7. März 2005, 15:00–18:00, Poster TU F
Ternary insulators: adsorption of water on MgSO4 · H2O(100) — •C. Tegenkamp1, V. Maslyuk1, T. Bredow2, and H. Pfnür1 — 1Institut für Festkörperphysik, Abteilung Oberflächen, Appelstr. 2 — 2Theoretische Chemie, Im Kleinen Felde 30, 30167 Hannover, Germany
The properties of the clean MgSO4 · H2O (100) surface (geometry, relaxation, electronic structure, stability) were investigated using ab initio and semi–empirical methods. Especially the influence of intrinsic water was compared to water molecules adsorbed onto the surface. Ab–inito calculations were performed both with density functional theory (DFT), using the Perdew–Wang exchange potential, and with Hartree–Fock (HF). Best agreement with the experimental band gap of 7.4 eV at the Γ–point of the Brillouin zone for the (100) surface was obtained by a linear combination of DFT and HF. The gap was determined with EELS at polycrystalline MgSO4 · H2O samples under UHV conditions.The valence band (VB) is formed mainly by the O2p–levels, whereas the S2p–states contribute mostly to the conduction band. A small electron density is located at the Mg atoms in the valence band region. The energetically preferred adsorption site of water within the unit cell of kieserite is above the Mg–atom. The electrostatic interaction between the Mg and the O–atoms of water is stabilized by two additional hydrogen bonds. The water induced changes of the density of states with respect to the separated systems were mainly limited to small energetic shifts towards lower binding energies (0.3eV). Similar results have been obtained for the chemically bound water, i.e. the DOS for MgSO4 · H2O and MgSO4 are almost identical in the energy range around the VB.