The dynamics of the expansion plasma produced by excimer laser
ablation of a silicon target into oxygen and mixed O2/Ar
atmosphere were studied by means of time-resolved imaging of the expanding
plume. Experiments were performed in pure oxygen, ranging between 0.13 and
13.33 Pa, and at different O2/Ar ratios at a fixed total
pressure of 13.33 Pa. The occurrence of a shock wave (SW) generated by the
supersonic expansion of the plasma was observed at high pressure values.
The presence of the SW had a strong influence on the structure of
SiOx thin films. In fact, silicon dioxide thin films were always
obtained in presence of the SW, irrespective of the oxygen content in the
gaseous mixture. On the contrary, suboxide thin films were obtained when
the expansion occurred at lower pressure values (no SW presence). The
temperature rise following the developing of the SW, is supposed to
enhance the oxygen molecules dissociation by increasing the efficiency of
the silicon oxidation reaction.