Nanostructures Studied by Atomic Force Microscopy : Ion Tracks and Nanotextured Films

The work presented in this thesis concernes two sorts of nanostructures: energetic-ion-impact-induced surface tracks and gas-deposited WO3 nanoparticles. Our aims to characterise these nanostuctures and understand the physical principles behind their formation are of general interests for basic science as well as of the field of nanotechnology. AFM studies of irradiated organic surfaces showed that individual ion impacts generate craters, most often accompanied by raised plastically deformed regions. Crater sizes were measured as a function of ion stopping power and incidence angle on various surfaces. Observed crater volumes were converted into estimates of total sputtering yields, which in turn were correlated with data from collector experiments. The observations were compared to predictions of theoretical sputtering models. The observed plastic deformations above grazing-incidence-ion penetration paths agree with predictions of the pressure pulse model. However, closer to the ion track, evaporative sputtering can occur. AFM images of gas-deposited WO3 nanoparticle-films indicated the formation of agglomerates. The size distribution of the agglomerates was measured to be log-normal, i.e. similar to the size distribution of the gas-phase nanoparticles forming the deposit. By simulations we could relatively well reproduce this observation. The agglomerates exhibited high thermal stability below 250°C when considering their size, implying that these porous films can be useful in applications involving elevated temperatures in the 250°C range. The appearance of the nanoparticles in the tapping-mode AFM images was sensitive to the free amplitude of the oscillating tip. We could show by model calculations that the high adhesion between the tip and the sample could account for some of these observations