Vibrational structure of ultrathin 8-hydroxyquinoline aluminum films studied by high-resolution electron-energy-loss spectroscopy

High-resolution electron-energy-loss spectra have been measured from submonolayer- and monolayer-thick 8-hydroxyquinoline aluminum (Alq) layers vacuum-deposited on metal substrates. Vibrational structures are different in the two cases. But no significant difference is found between the energy-loss spectrum of monolayer-thick Alq and the Fourier-transform infrared spectrum of bulk Alq. This seems to indicate that although there exists some weak bonding between the discretely adsorbed Alq molecules and the substrate, van der Waals interaction predominates upon the formation of a continuous Alq film. The structures in the loss spectrum are tentatively assigned. ©1999 The American Physical Society.