Velocity distributions of ions in the ablation plume of a Y1Ba2Cu3Ox target

The velocity distribution of ionic species in the plume was monitored by a time-of-flight mass spectrometer during laser ablation of Y1Ba2Cu3Ox. As oxygen pressure was raised, the velocity of Cu+ ions shifted to the slower side, and the width of the velocity distribution narrowed down to a minimum width at around 3×10−2 Torr. Beyond this pressure the width rapidly broadened. This change is qualitatively interpreted considering the dynamics in the flow of the supersonic expansion and thermal equilibrium, and is also discussed in connection with the surface morphology of ablated films.