Electron transport and spin phenomena in hybrid organic/inorganic systems

This thesis describes several experiments in hybrid organic/inorganic systems, in which electron transport and/or spin behavior is studied. The basic concepts of organic electronics and spintronics are given, to understand the described spin-valve experiments. The problems and obstacles for injecting a spin-polarized current into organic materials and the potential of using organic single-crystals in spintronic devices are discussed. Different methods for fabricating organic single-crystal FET devices with FM electrodes are explained. First, the growth of organic single-crystals is discussed. Then, the fabrication of FM electrodes with shadow masks, photo- and e-beam lithography is explained. The interface of fabricated FM electrodes and organic materials is investigated. UV photoemission spectroscopy and X-ray photoelectron spectroscopy are performed to study the energy level alignment. The effect of the lithography processes on the spin injection properties of the FM electrode and a cleaning step applied to the interfaces are investigated. Measurements on rubrene single-crystal FETs with FM/tunnel barrier electrodes are discussed. The critical spin-valve properties of these devices are investigated and it is shown that this FET has the potential of being used as a spin valve. The current flowing through the device can be fitted to a back-to-back Schottky model, which show that electrons are injected via a well-defined tunnel barrier fabricated on top of the FM electrodes. Transferring Au electrodes to organic single-crystals by soft elastomeric stamps, with and without the facilitation of organic molecules, is investigated. Measurements in the space-charged-limited-current regime and on FET devices are presented and discussed. FM nanoparticles (NPs), capped with organic ligands, are discussed. A systematic study of the annealing of these NPs in solution at relative low temperatures is described. The annealing is needed to obtain high magnetocrystalline anisotropy. The low-temperature annealing leaves the organic ligands intact, which can be used for patterning. Experiments are performed on two-dimensional organic spin systems to study the interaction of the spins with their environment. The system consists of a thin Au film covered with a monolayer of molecules containing an unpaired spin. The signature of the Kondo effect, a local resistance minimum as a function of temperature, is observed under certain conditions. The behavior of this effect in the presence of a magnetic field is also investigated.