Polyatomicity and kinetic energy effects on surface polymerization by ion-assisted deposition

Various techniques are used to probe surface polymerization by ion-assisted deposition (SPIAD) of films prepared from 100 and 200 eV non-mass-selected thiophene ions and evaporated α-terthiophene (3T) neutrals. C4H4S+, C4D4S+ (and fragments thereof), and Ar+ ions are compared to elucidate polymerization mechanisms in SPIAD. Desorption ionization on oxidized silicon mass spectrometry is used to probe the nature of the polymerized products of SPIAD as well as ion incorporation into the film. Mass spectra, Fourier transform infrared spectra, and X-ray diffraction all indicate higher molecular weight species and less fragmentation of 3T for 100 eV thiophene ions. Mass spectra indicate thiophene ions behave both as catalysts and reagents in polymerization. Despite obvious differences in film chemistry, quartz crystal microbalance measurements show SPIAD film thicknesses are the same for both the polyatomic and atomic ions at both ion energies. UV-vis absorption and photoluminescence are found to depend upon the differing chemical composition and structure of the films which in turn are controlled by the polyatomicity and kinetic energy of the incident ions.