Atom probe tomography analysis of poly(3-alkylthiophene)s

Pulsed-laser atom-probe tomography is used to compare the field-evaporation mass spectrum and spatial distribution of molecular fragments from various poly(3-alkylthiophene) films deposited on sharpened aluminium specimen carriers using two different deposition methods. Films deposited via a modified solution-cast methodology yield small fragments with a uniform structural morphology whereas films deposited via an electrospray ionization methodology yield a wide range of fragments with a very non-uniform structural morphology. The main field-evaporated chemical species identified for both deposition types were, in order of typical relative abundance, C₂H₅⁺, CH₃⁺, C₂H₄⁺, followed by C₃H₇,₈⁺/SC⁺ and SCH⁺. Thick electrospray depositions allowed investigation of the influence of laser-pulse energy on the analysis. Evidence is presented supporting the presence of a critical laser-pulse energy whereby changes in film morphology are signalled by the appearance of a new mass fragment at 190 Da.