Scanning tunneling microscopy and spectroscopy on surfaces, interfaces, and atomic clusters.

In this work we have studied the dependency of the properties of electrons on their confinement conditions. In order to obtain these different confined electron systems, we have investigated nanoparticles on both Au(111) and NaCl, adatoms on and vacancies in NaCl, and the 2-DEG formed at the NaCl/Au(111) interface.The study of confined electrons necessarily consisted of two parts: first we needed to determine the geometric structure of the entire system, and secondly the electronic properties of the system had to be measured. In order to address both criteria, this study was performed using scanning tunneling microscopy (STM) to determine the morphology of the systems under study, combined with scanning tunneling spectroscopy (STS) in order to simultaneously measure their electronic properties. Measurements were performed at low temperatures and under ultra-high vacuum conditions, in order to ensure cleanliness and to obtain high resolution results.In the first experimental part of this work, we demonstrated that on the nanoscale a system is more than the sum of its parts, as the catalytic activity of TiOx nanoparticles deposited onto Au(111) showed. Experimentally a mutual influence between the nanoparticles and the metallic surface was measured. It was demonstrated that the deposited TiOx nanoparticles are hemispherical and that they remained stable on the Au(111) surface at elevated temperatures, while the study of the electronic properties revealed an electron transfer from the nanoparticles to the Au(111). Taken together these results led us to a better understanding of the mechanism behind the catalytic activity of the combined system, i.e. cooperative effects between the TiOx and the Au(111).However, for the aim of this work, the investigation of individual systems of confined electrons, the cooperative effects could mask the intrinsic properties of the confined electron systems under study. Therefore, to minimize the influence of the substrate the second part of this work consisted of investigating a means to isolate the nanosystems from the metallic substrate.Thin layers of NaCl were chosen to fulfill this requirement, and their properties were studied in detail. Morphologically, the most obvious findings for this part of our work were that NaCl grows in flat stoichiometric layers on Au(111), and that the NaCl thickness could be controlled by post-annealing. Electronically, it was found that the interplay between the herringbone reconstructed Au(111) surface and the NaCl played an important role. Firstly, because it led to a tune ability of the NaCl/Au(111) interface state depending on the NaCl thickness. Secondly we showed that due to the interplay between the Au(111) surface reconstruction and the NaCl, both the Na and the Cl atoms of the NaCl could be imaged, something not done before.Finally, in the third part of this work individual nanosystems were studied using the NaCl as a substrate. This part built up from the smallest possible nanosystems, F-centers and adatoms, where electronic properties akin to molecular orbitals were observed, to Co clusters deposited onto trilayered NaCl films. The topography of all three systems under study was determined with atomic precision, which is essential if one wants to build devices based on the atomic understanding of small systems. The electronic properties of these systems were determined with the same precision, leading to a complete experimental picture of the confined electron systems.status: publishe