Optical and chemical properties of polythiophene films produced via surface polymerization by ion-assisted deposition

Polythiophene films are produced via surface polymerization by ion-assisted deposition (SPIAD), in which 55-200 eV thiophene ions and alpha-terthiophene (3T) neutrals are co-deposited on surfaces. These SPIAD polythiophene films display unique optical properties in their photoluminescence and UV/vis absorption compared with films prepared by either 3T or direct thiophene ion deposition only. The optical properties of SPIAD polythiophene depend on the deposited ion-to-neutral ratio and ion energy. Ion-to-neutral ratios of 1/100 cause a red shift in the photoluminescence of SPIAD films compared with 3T films whereas ratios of similar to1/400 cause a blue shift. Ion energies at 100 eV showed the most enhanced photoluminescence and UV/vis absorption compared with 3T films. Mass spectrometry indicates that a variety of higher molecular weight oligomers with some masses exceeding [3T](3) are formed by SPIAD. UV/vis spectra and X-ray photoelectron spectroscopy support the formation of a distribution of oligomers, while the latter method reveals elemental content consistent with polythiophene.