Étude par microscopie à sonde locale des propriétés électriques de monocouches auto-assemblées de molécules photo-commutables sur substrats ferromagnétiques

This thesis focuses on electrical transport through self-assembled monolayers (SAMs) of photoisomerisable compounds grafted on ferromagnetic materials (FMs) for applications at the frontier between molecular electronics and spintronics. These systems have been characterized by conductive atomic force microscopy under ambient conditions and ultra-high vacuum. FM-SAM/tip junctions are expected to show resistance photoswitching during irradiation cycles. The first FM-SAM couple consists of lanthanum strontium manganite (LSMO) and a diarylethene derivative (DDA). We show that the switch-off of LSMO-DDA after UV irradiation, characterized by a ratio 5 of current, does not result from DDA isomerization but rather from LSMO heating. Similarly, electric field and strain applied by the tip also lead to the switch-off of the LSMO. Nevertheless, this last effect is disrupted when LSMO is protected by a DDA SAM. The second system studied is an azobenzene derivative grafted on cobalt. Co-AzBT exhibits an ON/OFF current ratio up to 21 at +0,5 V, partially reversible. Tip-induced switch-off was also observed on air exposed cobalt but is quasi-absent when the substrate is protected by a SAM. Despite showing the difficulties inherent to the use of FMs, this work sheds light on new ways to realize hybrid opto-spintronics molecular devices, triggered by isomerization and spin-polarized transport. ; Ce manuscrit traite du transport à travers des monocouches auto-assemblées (self-assembled monolayers, SAMs) de molécules photoisomérisables greffées sur des matériaux ferromagnétiques (FMs) pour des applications à la frontière de l'électronique moléculaire et de la spintronique. Ces systèmes sont étudiés par le mode conductif du microscope à force atomique, à l'air et sous ultravide. Il est attendu que les jonctions FM-SAM/pointe présentent une photo-commutation de résistance au cours de cycles d'irradiation. Un premier couple FM-SAM allie le manganite de lanthane dopé au strontium (LSMO) à un dérivé de diaryléthène (DDA). Il est ...