X-ray and electron induced oligomerization of condensed 3-hexylthiophene

MgK alpha X-ray and low energy electron irradiation of thick physisorbed layers of 3-hexylthiophene condensed on clean gold at 145 K results in formation of an organic film that does not desorb when the sample is warmed to room temperature. Cls and S2p X-ray photoelectron spectra of the X-ray and electron-formed films are similar to those of chemically synthesized poly(3-hexylthiophene). Ultraviolet photoelectron spectroscopy indicates the presence of thiophene ring electronic states, consistent with retention of conjugation. Comparison of the valence spectra with condensed monomer and poly(3-hexylthiophene) indicates that the X-ray and electron-formed films are oligomeric rather than polymeric, in contrast to related studies on condensed thiophene. This difference suggests that the aliphatic side chain reduces monomer mobility during the polymerization process, leading to shorter chains. Electron bombardment with 5 keV electrons results in films of micron thickness, as determined by profilometry. The ability to lithographically oligomerize the monomer is demonstrated by forming a dot with an electron beam. FTIR spectroscopy of electron-formed films shows vibrations consistent with the formation of linearly oligomerized 3-hexylthiophene.