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

MgK alpha X-ray and low energy electron irradiation of thick physisorbed la yers of 3-hexylthiophene condensed on clean gold at 145 K results in format ion of an organic film that does not desorb when the sample is warmed to ro om temperature. Cls and S2p X-ray photoelectron spectra of the X-ray and el ectron-formed films are similar to those of chemically synthesized poly(3-h exylthiophene). Ultraviolet photoelectron spectroscopy indicates the presen ce of thiophene ring electronic states, consistent with retention of conjug ation. Comparison of the valence spectra with condensed monomer and poly(3- hexylthiophene) indicates that the X-ray and electron-formed films are olig omeric rather than polymeric, in contrast to related studies on condensed t hiophene. This difference suggests that the aliphatic side chain reduces mo nomer mobility during the polymerization process, leading to shorter chains . Electron bombardment with 5 keV electrons results in films of micron thic kness, as determined by profilometry. The ability to lithographically oligo merize 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.