The adsorptions of polystyrene, poly(methoxystyrene), poly(acrylamide), and poly(acrylic acid) on aluminum oxide are investigated with inelastic electron tunneling spectroscopy. Comparison with infrared data for thin polymer films of the polymer samples gives insight into the adsorbed polymer configuration. Data indicate that poly(styrene) is weakly physisorbed to aluminum oxide, while poly(methoxystyrene), poly(acrylamide), and poly(acrylic acid) react to form strong bonds with the oxide surface. On the basis of this data, adsorption mechanisms are suggested for each of the polymers. Poly(acrylamide) adsorbs via a protonation of the amine group by the surface hydroxyl groups. Poly(4-methoxystyrene) forms a phenolate ion and can react further with the aluminum surface centers. Poly(acrylic acid) adsorbs to the oxide surface in a manner analogous to that of small organic acids such as the carboxylate ion.
Inelastic electron tunneling spectroscopy in molecular junctions showing quantum interference
