Characterization of high-quality NTCDA films on metal substrates

The bonding of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) to the single crystal substrates Ag(111) and Cu(100) and its molecular orientation were investigated by photoelectron (XPS, UPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Vapour deposited NTCDA films exhibit high orientational order in the mono- and multilayer regime, respectively. NTCDA monolayers are strongly bound to the metal substrates via the conjugated pi-system of the naphthalene core which leads to a parallel orientation of the molecular plane with respect to the substrate. In multilayers the molecular orientation strongly depends on the substrate temperature during deposition. Film preparation at 285 K results in upright standing molecules beyond the monolayer, whereas substrate temperatures below about 200 K yield an uniform molecular orientation with the molecular plane parallel to the substrate. (C) 1998 Elsevier Science B.V. All rights reserved.