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SUMMARY:Observation of a distinct surface molecular orientation in films o
 f a high mobility conjugated polymer - Dr. Chris McNeill\, Monash Universi
 ty\, Australia
DTSTART:20130220T143000Z
DTEND:20130220T153000Z
UID:TALK43081@talks.cam.ac.uk
CONTACT:Dr. Girish Lakhwani
DESCRIPTION:The molecular orientation and microstructure of films of the h
 igh-mobility semiconducting polymer poly(N\,N-bis 2-octyldodecylnaphthalen
 e-1\,4\,5\,8-bis\ndicarboximide-2\,6-diyl-alt-5\,5-2\,2-bithiophene) (P(ND
 I2OD-T2)) are probed using a combination of grazing-incidence wide-angle x
 -ray scattering\n(GIWAXS) and near-edge x-ray absorption fine-structure (N
 EXAFS) spectroscopy. In particular a novel approach is used whereby the bu
 lk molecular orientation and surface molecular orientation are simultaneou
 sly measured on the same sample using NEXAFS spectroscopy in an angle-reso
 lved transmission experiment. Furthermore\, the acquisition of bulk-sensit
 ive NEXAFS data enables a direct comparison of the information provided by
  GIWAXS and NEXAFS. By comparing the bulk-sensitive and surface-sensitive 
 NEXAFS data a distinctly different molecular orientation is observed at th
 e surface of the film compared to the bulk. While a more 'face-on' orienta
 tion of the conjugated backbone is observed in the bulk of the film\, cons
 istent with the lamella orientation observed by GIWAXS\, a more 'edge-on'\
 norientation is observed at the surface of the film with surface-sensitive
  NEXAFS spectroscopy. This distinct edge-on surface orientation explains t
 he high in-plane mobility that is achieved in top-gate P(NDI2OD-T2) field-
 effect transistors (FETs)\, while the bulk face-on texture explains the hi
 gh out-of-plane mobilities that are observed in time-of-flight and diode m
 easurements. These results also stress that GIWAXS lacks the surface sensi
 tivity required to probe the microstructure of the accumulation layer that
  supports charge transport in organic FETs and hence may not be appropriat
 e for correlating film microstructure and FET charge transport.
LOCATION:Kapitza Building Seminar Room\, Cavendish Laboratory\, Department
  of Physics
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