PRECOVERAGE-DEPENDENT MOLECULAR-ORIENTATION OF BIG ORGANIC ADSORBATES- NDCA ON NI(111) AND O NI(111)/

The orientation and chemical bonding of big organic adsorbates may str ongly depend on the properties of the surface, e.g. on the precoverage . This is demonstrated for the planar molecule naphthalene-(1,8)-dicar bonic acid anhydride (NDCA) on a clean and oxygen p[2 X 2] precovered Ni(111) surface by TPD and NEXAFS experiments. On clean Ni(lll) NDCA l ies flat on the surface and bonds via the naphthalene pi system, where as on the O-precovered substrate an upright orientation with bonding v ia the anhydride group is observed. Arguments are given for the reason for this drastic change of adsorbate geometry which has some implicat ions for 'tailoring' organic/inorganic interfaces.