Renaud Demadrille

Pi-Conjugated Molecular Nanowire Stacks Investigated by Frequency-Modulation Atomic Force Microscopy in the qPlus Configuration

Self-assembled pi-conjugated nanowire stacks were imaged using a tuning-fork probe mounted in the qPlus configuration in frequency modulation mode under ultrahigh vacuum. High resolution topographic and dissipation images demonstrate the applicability of such probes to soft conjugated materials, with sub-molecular resolution achieved perpendicular to the stacking axis. A new insight is gained from the damping contrast into the local mechanical properties of edge-on pi-conjugated stacks.

Comparative study of optoelectronic properties of various Europium complexes used in organic electroluminescent structures

In order to obtain a red emission with organic electroluminescent device, we realized multilayer structures using various Europium complexes as emitting layer. The multilayer structures were obtained with the emitting layer deposited on a ITO substrate; a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) layer was used as hole blocking layer and a tris-(8-hydroxyquinoline) aluminium (Alq3) layer as electron transport layer. Cathode of the devices was realized with a calcium layer covered with an protective aluminium layer. Two different europium complexes have been tested: Eu (TTA)3 phen (TTA = thenoyltrifluoroacetone), Eu (DTP)3 (dipphen) (DTP = 1,3-di(2-thienyl)propane-1,3-dione, dipphen = 4,7-Diphenyl-1,10-phenanthroline) The Europium complexes were inserted in a poly-9-vinylcarbazole (PVK) matrix and the spin-coating process was used to obtain the emitting layers. The maximum emission of the OLEDs are centered around 610 nm according to the 5D0 → 7F2 transition of the rare earth. Europium complexes absorption spectra in chloroform and electroluminescence spectra are presented. Current-voltage and luminance-voltage characteristics are also presented and we discuss about the results obtained with various molar concentration of Europium complexes in the PVK matrix.