Unoccupied electronic states in ordered PTCDA and H2Pc thin films grown onInAs and InSb: a resonance HREELS study

Citation
Pj. Unwin et al., Unoccupied electronic states in ordered PTCDA and H2Pc thin films grown onInAs and InSb: a resonance HREELS study, SURF SCI, 482, 2001, pp. 1222-1227
Citations number
22
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
SURFACE SCIENCE
ISSN journal
0039-6028 → ACNP
Volume
482
Year of publication
2001
Part
2
Pages
1222 - 1227
Database
ISI
SICI code
0039-6028(20010620)482:<1222:UESIOP>2.0.ZU;2-X
Abstract
High resolution electron energy loss spectroscopy has been used to investig ate the unoccupied electronic states of ordered thin films of perylene-3,4, 9,10-tetracarboxylic dianhydride (PTCDA) and free-base phtlialocyanine (H2P c) grown on InAs and InSb substrates. Measurement of the vibrational excita tion functions over a wide range of electron beam energies shows that both molecules exhibit strong resonant behaviour due to temporary negative ion f ormation. For PTCDA/InAs(1 1 1)A, there is no mode selectivity and all the vibrational modes of the molecule are resonantly enhanced at 2.2 eV. By con trast, two resonances are observed for H2Pc/InSb(1 0 0) at 0.8 and 7.0 eV r espectively, with the higher energy resonance demonstrating mode selectivit y. Identification of the resonant states is assisted by comparison to previ ous near edge X-ray absorption fine structure measurements for PTCDA and Pc films. (C) 2001 Elsevier Science B.V. All rights reserved.