AVS 47th International Symposium
    Organic Films and Devices Thursday Sessions
       Session OF+EL+SS-ThM

Paper OF+EL+SS-ThM6
Growth of Films of Thiophene Oligomers by Seeded Supersonic Beams to Improve Control on their Quality and Properties

Thursday, October 5, 2000, 10:00 am, Room 313

Session: Organic Thin Films
Presenter: S. Iannotta, CeFSA - Research Center CNR-ITC for the Physics of Aggregates, Italy
Authors: S. Iannotta, CeFSA - Research Center CNR-ITC for the Physics of Aggregates, Italy
T. Toccoli, CeFSA - Research Center CNR-ITC for the Physics of Aggregates, Italy
A. Boschetti, CeFSA - Research Center CNR-ITC for the Physics of Aggregates, Italy
P. Milani, INFM - Universit@aa a@ di Milano, Italy
S. Ronchin, INFM - Universit@aa a@ di Trento, Italy
A. Podest@aa a@, INFM - Universit@aa a@ Bicocca, Italy
Correspondent: Click to Email
The growing interest in pi-conjugated organic molecular materials and polymers, driven by wide potential technological impact in electronics and photonics, still faces severe limitations. Applications would be much more favored by improving control on morphology and structure in the solid state. Standard growth methods are based on the self-assembling of the molecules resulting more or less affected by the interaction with the substrate. Very often the resulting films show an inadequate ordering. These problems become severe as the thickness increases over a few monolayers. Fully considering the major role played by the initial state of the molecules at early stages of growth, we approached the problem combining a supersonic free jets that permit to control kinetic energy, momentum and flux with a UHV deposition apparatus. We perform the deposition and simultaneously control the initial state of the seeded organic molecules by varying the parameters of the supersonic expansion (dilution, temperature of the source, form and diameter of nozzle, etc) [P. Milani and S. Iannotta, Synthesis of Nanophase Materials by Cluster Beam Deposition, Springer, Berlin (1999)]. We have prepared a series of films of alpha quaterthiophene that are then characterized by optical measurement, TM-AFM and X-ray diffraction. We report an overall strong evidence of an unprecedented control on morphology, structure and optical response that correlate well to the beam's parameters. PL spectra at low temperature show the vibronic molecular structure very well resolved depending on the initial state of the oligomer in the beam. Films, several hundreds nm thick, show a high degree of ordering with surface morphologies characterized by layered structures of molecular height. X-ray diffraction confirms the high degree of ordering induced by the growth from highly supersonic beams. Correlation between morphology, degree of ordering and the optical response of these films will be discussed.