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 strongly depend on the properties of the surface, e.g. on the precoverage. This is demonstrated for the planar molecule naphthalene-(1,8)-dicarbonic acid anhydride (NDCA) on a clean and oxygen p[2 × 2] precovered Ni(111) surface by TPD and NEXAFS experiments. On clean Ni(111) NDCA lies flat on the surface and bonds via the naphthalene π system, whereas on the O-precovered substrate an upright orientation with bonding via the anhydride group is observed. Arguments are given for the reason for this drastic change of adsorbate geometry which has some implications for ‘tailoring’ organic/inorganic interfaces.