Nanoparticle formation in nanoporous structures and applications

In the recent years the scientific community demonstrates an increasing interest in the study of nanoparticles and their properties, such as interaction with a surface and the adsorption/desorption characteristic. The latte properties, as well the formation and growth of nanoparticles, can be controlled by a proper light source. On the other hand having a much larger specific surface to increase the adsorbed amount of atoms, is a desirable characteristic of the system. That is on of the reason of the large exploitation of nanoporous material in many different research fields. Porous glass presents a wide variety of benefits: thermal and chemical stability, low production cost, easiness of handling and large value of specific surface area, which can be of the order tens square meters per grams. This thesis work falls into the context described above, in particular it aims to investigate the adsorption/desorption process of alkali atoms onto different randomly oriented pores structures, as well the formation of aggregates in the pores of the adsorbed atoms by using different external light sources. The control of the desorption process as well as the formation and the desorption of nanoparticles make use of two light induced process: Light Induced Atomic Desorption or LIAD and the Surface Plasmon Induced Desorption. The main difference between these two effects, beside the physics behind the two effects is intrinsically different, is that for the latter is required a resonant light source resonant with the plasmonic oscillation while for the LIAD it is not needed any resonant wavelength. The main and newer part of the work is done in a chamber were is present an Ultra High Vacuum regime. Most of the studies on this topic were performed in vapor filled cells. The use of an Ultra High Vacuum regime for this work is done to overcome some drawback of the vapor cells, such as the impossibility to change atomic species once that a cell is built or the difficult controlling of the atomic density. Indeed in this apparatus the loading process is done with an externally removable dispenser controlled by a current flowing into it. Hence the loading process is no more continuous an can be switched off by switching off the flowing current. Once the UHV regime is reached, the first step is the loading of the porous sample. Then the adsorption properties at different wavelengths are studied as well as that eventual desorption of the atomic specimen. The formation of nanoparticles in the porous structures are induced by an external light source under different condition of intensity and illumination time. Similar studies are also performed in alkali vapor filled cells, in order to compare the results. There were performed simultaneously measurements by on the optical signal and electric signal by means of a channeltron. The measurements performed in this work showed that by using porous glass, with different average pores size and under an appropriate illumination, it is possible to exploit the LIAD effect to enhance the aggregation of Rb nanoparticles in UHV regime. The most satisfying sample revealed to be a film of nanoporous alumina of 300 nm thickness.