Statistical studies of heating under light ions microbeams: measures, theory and physical effects

Light ion microbeams of a few MeV, such as the one obtained in the Pierre Sue Laboratory, are used to determine chemical composition of materials at a micrometer scale. The interactions between the ions and the sample atoms produce first events, which are necessary for analysis, and secondary effects such as sputtering. The aim of this thesis is the study of one of these latter effects, not much studied until today: the heating due to the slowing down of ions in the sample. Our measures allowed us to observe a mean heating - in keeping with theory - of about 10 K/mW at 10 micrometers from the impact of a typical beam on samples with a thermal conductivity as small as glass one. Nevertheless a main discovery of this work is the evidencing of heating fluctuations arising from the beam current ones. The measure of these fluctuations showed they might produce major physical effects. Actually, we observed instantaneous heating ten times higher than the above mean value, during typical periods of about 10 ms in the immediate vicinity of the beam impact. A statistical solving of the equation of the heat diffusion allowed us to describe the fluctuation behaviour and explain the reason why these fluctuations can dominate the mean heating in the beam vicinity. These results are presented in the first two sections of the thesis. In the third and last one, we show a physical effect induced by the heating under beam: the vaporisation of a thin Zinc film deposited on a glass plate. (author)