In this thesis work, we plan to study the spin injection via ferromagnetic electrodes and transport through organic materials in the form of thin layers, small molecules or even a single molecule. In order to achieve this, two original devices will be investigated:

- Systems based on break junctions, which consist in breaking a suspended bridge of a few 100 nm in widthand micrometer in length covered with a thin layer of organic materials. These nanostructures are defined on Kapton substrates which can be bent in order to generate a large strain in the bridge leading to breakage. We have recently proved that the system can be scaled down to a small number of polymers (providing a very diluted layer of polymers is deposited) and even possibly to a single organic molecule.

- Ferrite-based magnetic tunnel junctions consisted by two ferromagnetic electrodes separated by an organic thin layer: AFe2O4/organique/(Co, Fe?). Ferrites (Fe3O4, CoFe2O4?) are very attractive oxides for the generation of a highly spin-polarized current at room temperature.

Concerning the organic layers, we will study semi-conducting (Alq3, pentacene, rubrene?) or insulating molecules. In the second case, non-functionalized molecules such as polymers (PMMA?) or short molecules with a functionalization at the termination will be investigated.