04 Mars – Thesis defense - Frédéric Dutin

14 h Amphi 3 - building A9 (Talence campus)

Linear and non-linear spectroscopy of conducting polymers on THz domain.

This thesis project aims to study transport mechanisms in conducting polymers PEDOT/PSS and PEDOT/PSTFSIK in the terahertz (THz) domain. These two polymers come from LCPO laboratory.
First of all, we studied intrinsics properties of these materials in the THz domain with a THz-TDS experiment. This drove us to show that their transmission is quasi-constant in the THz domain and that the intrinsic conductivity is larger for PEDOT/PSS than PEDOT/PSTFSIK. This last result has been obtained by using two differents fitting models of conduction. The first model, so-called Drude-Smith model, extend the Drude model by adding a trap parameter. It also possess only few fitting parameters. The second one, the Dyre model, take into account of the grain structure of polymers. Nevertheless, it has several fitting parameters. We obtained a direct current conductivity of polymers that is in excellent agreement with LCPO measurements.
Among these, we caracterized the behavior of PEDOT/PSS and PEDOT/PSTFSIK under a femtosecond pulse centered in the bipolaronic band. We also have the THz pulse. By using Drude-Smith and Dyre models, we were able to study the change of conductivity induced by the femtosecond pulse in the THz domain. In this case, we supposed that fitting parameters have to be a function of the delay between the femtosecond pulse and the THz pulse.
Finally, by studying PEDOT/PSS and PEDOT/PSTFSIK responses for differents pump intensity in a full optic experiment, where we pumped on the bipolaronic band and probed on the polaronic band, we were be able to give a possible scenario for the impact of the optical pump in these materials.

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