Study of electronic structure of carbon and silicon particles

The basic research on the properties of carbon and silicon is focused on the comprehension of the covalent bond which is one of the four types of bonds, among Van der Waals, metallic and ionic. The nature of the bond strongly affects the properties of the samples. However, the difference between carbon and silicon is object of intense investigation.
The peculiarity of carbon in forming a wide variety of bonds interests mostly organic chemists who consider the chemical behaviour of carbon fundamental for the development of the life. About fifty years ago, the scientific society started to investigate the physical properties of silicon and since then a wide range of technological applications in the microelectronics industry has been developed.
Although these two elements have been extensively studied, the interest of the scientific community has never diminished. In the last two decades the research on carbon and silicon has received a strong impulse since two discoveries have multiplied the perspectives of applications:
• The existence of pure carbon molecules in the form of hollow cages with highly symmetric structure – fullerenes.
• The luminescence of silicon particles. Both are results of experiments on particles, more precisely on atomic clusters.
These results confirm the expectation that properties of samples change with their dimensions. The research on clusters containing from two to several hundred atoms offer the possibility of studying the transition from molecules to crystalline solids. Along with the interest in the physical properties of atomic clusters, there is a corresponding interest in the chemical properties. In addition, there is a strong technological interest in clusters as unique small systems, for example, as catalysts or for making tailored optical materials. In the particular case of carbon clusters, fullerenes and the related carbon nanotubes have attracted the interest of chemists, physicists, and material scientists because of their promise as superconductors, molecular containers, templates for derivatives with tailormade electronic properties, and nanometer wide carbon fibers.
These clusters constitute a third form of elementary carbon (besides graphite and diamond) and afford a rich exohedral, endohedral, and cage-surface substitution chemistry, which makes them ideal candidates for building blocks of a carbon-based nanotechnology.
Silicon clusters do not show equilibrium symmetric fullerene structures like carbon [Nog97], but rather exhibit more compact geometries. Nevertheless silicon clusters of small and intermediate size have received a great deal of attention for the promising technological applications in optoelectronics. The present dissertation is focused on studies of physical properties of size-selected carbon and silicon clusters. The research work is experimental - the electronic structure of small clusters has been investigated employing photoelectron spectroscopy. Fragmentation spectroscopy has been performed as well for a better comprehension of the photoelectron results.