Dresden 2006 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 3: Poster Session

DF 3.8: Poster

Montag, 27. März 2006, 09:30–17:00, P1

Ferroelectric properties of Langmuir-Blodgett PVDF-Copolymer films — •Raphael Tadros-Morgane and Herbert Kliem — Institute of Electrical Engineering Physics, Saarland University, D66123 Saarbruecken Campus, Germany

Langmuir-Blodgett films are designed as a stack of mono-molecular layers piled up sequentially onto a solid substrate. These layers are transferred from surface active agents trapped at the interface between two dissimilar phases, either liquid-liquid or liquid-gas [1]. However, the P(VDF-TrFE) copolymer is not well suited to this technique. Nevertheless, it is possible to realize ferroelectric thin films using this method. To reach this goal, transfers on a glass substrate were realized for a surface pressure of the interface ranging from 0.5 mN/mm to 5 mN/mm and for concentrations of the copolymer from 0.1 g/l to 0.0001 g/l. For a given number of transfers, here 30, the optimal pressure is about 3mN/mm with a concentration of 0.01 g/l. These samples show true ferroelectric properties like hysteresis loops and switching of the polarization. Films of P(VDF-TrFE) with thicknesses ranging from 2.7 nm to 64 nm prepared by a Langmuir-Blodgett technique at the Institute of Crystallography in Moscow, were electrically characterized. It is found that the coercive fields increase with decreasing sample thickness following a power law. The switching of the polarization yields stretched exponential functions with time constants t dependent on thickness and temperature. t increases with decreasing thickness and is thermally activated [2]. Also the initial polarization curves obtained from the unpolarized state are thickness and temperature dependent.