Abstract EN:

One of the most urgent tasks in the field of molecular electronics is to understand and tune the contact between molecules and a metal lead. Scanning tunneling microscopy and spectroscopy (STM and STS) represent a unique tool to correlate electronic and structural properties at the nanoscale, such as the impact of geometry on the spin-transport through a single molecule. In this perspective, the work presented here employs STM/STS as well as spin-polarized STM/STS to focus on key phenomena of the conductance of nanoscaled objects, e. G. Metallic islands, single atoms and molecules, the results always being compared to theoretical calculations. After a brief introduction of the STM/STS techniques employed, Chapter 1 provides some technical details regarding the sample and tip preparation. Chapter 2 is dedicated to the characterization of the Cu(111) surface and of cobalt islands grown on this surface. Chapter 3 focuses on individual atoms adsorbed on cobalt islands. The polarization of the local density of states (LDOS) above the atoms is discussed in relation with the polarization of the surface. Surface induced states and atomic resonances are shown to determine the LDOS above the atom, as well as the spin-polarization around the Fermi energy. In the last two chapters, results are obtained on Cobalt-Phthalocyanine and C60, both molecules being model systems for future molecular electronic devices. Molecular conductance channels and the spin-polarization of a single molecule (Chapter 4), as well as a negative differential conductance, which originates from an energy-dependent match and mismatch of molecular orbitals and electronic tip states (Chapter 5), are revealed.