Chemistry at the Interface of α-Sexithiophene and Vapor-Deposited Ag, Al, Mg, and Ca: A Molecular View

Abstract

Interfacial chemistry of thiophene-based polymers and oligomers in contact with low work function metals is of interest for organic electronic devices. Herein, interfacial reactions of the model thiophene-based oligomer, α-sexithiophene (α-6T), in ultrathin (5 ML) films with vapor-deposited Ag, Al, Mg, and Ca are investigated using surface Raman spectroscopy and X-ray photoelectron spectroscopy under ultrahigh vacuum conditions. Although typically considered an electron donor, results indicate that α-6T is reduced by Al and Ca. The reduction product with Al is the tetrahydrothiophene, whereas complete degradation of the thiophene cores occurs with Ca with the formation of calcium sulfide. In contrast, for the higher work function Ag, contact doping from α-6T to Ag nanoparticles is observed, inducing the formation of polaron states at the interface. Inter-ring torsion by the C–C bond rotation is also induced by electron sharing between α-6T and Ag. Mg, which is expected to undergo electron transfer in a ma...