Site-Specific Charge-Transfer Screening at Organic/Metal Interfaces

Site-specific core hole screening effects at organic/metal interfaces were studied using core-level X-ray photoemission spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), and valence band ultraviolet photoemission spectroscopy (UPS). As model molecules, we chose zinc phthalocyanine (ZnPc) and its perfluorinated derivative ZnPcF(16) evaporated on Au(100). For the first molecular layer on the metal surface, we observe for both molecules a clear splitting of the Zn L(3)M(4,5)M(4,5) signal clue to strongly increased screening in the double-hole final states In contrast, F KL(2,3)L(2,3). Auger spectra do not show additional features at any stage of deposition. Site-dependent screening effects are discussed in terms of polarization and charge-transfer screening.