Adsorption study of thin films of terephthalic acid and substituted benzoic acids on HOPG studied by Metastable Induced Electron Spectroscopy and Ultraviolet Photoelectron Spectroscopy

The adsorption behavior of thin films of 4-alkoxybenzoic acids (with either hydroxy-, methoxy-, propoxy-, pentoxy- and decoxy-chains) and terephthalic acid, evaporated on a Highly Oriented Pyrolytic Graphite (HOPG) surface was studied. The orientation of the molecules was characterized by Metastable Induced Electron Spectroscopy (MIES) and Ultraviolet Photoelectron Spectroscopy (UPS(HeI)). On HOPG the 4-alkoxybenzoic acids and the terephthalic acid show a layer like growth at the beginning. Since the MIE spectra for the molecules on HOPG show all molecular orbitals, especially the π orbitals of the phenyl ring, a flat laying orientation on the graphite surface is assumed. The only exception is observed for 4-decoxy-benzoic acid. After a coverage of approximately 1 monolayer (ML) the spectrum is dominated by the spectral features of the alkyl structures.