Adsorption analysis of thin films of terephthalic acid on Au and Al studied by MIES, UPS and XPS

Highlights: • Adsorption study of terephthalic acid (TPA) with MIES. • Flat adsorption of the molecules on gold. • Upright adsorption of the TPA molecules on oxidized aluminum. - Abstract: The adsorption behavior of thin films of terephthalic acid (TPA) evaporated on a gold surface as well as on an aluminum foil was studied. The orientation of the molecules was characterized by metastable induced electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS). To make sure that the evaporation of TPA is nondestructive, additional X-ray photoelectron spectroscopy (XPS) was performed. These measurements also exclude any radiation damage. TPA on the gold surface shows a well-ordered layer growth up to 7.5 nm. Since the MIES spectra show both the acid structure and the phenyl group, a flat-laying orientation is assumed. In contrast, the phenylic carbon structure could not be observed while evaporating TPA on the oxidized aluminum foil. The MIES/UPS spectra only show the COOH group. To exclude a random arrangement of the molecules we also performed low temperature measurements. It can be concluded from these measurements, in addition to the fact that the work function increases during the evaporation, that TPA has a perpendicular arrangement on the aluminum foil