Internal energy distributions of laser ablated species from YBa 2Cu3O7-δ
Abstract
The first simultaneous measurements of the ground-state translational, rotational, and vibrational energy distributions of a laser ablated diatomic molecule (YO) liberated during a 351 nm excimer laser ablation of YBa 2Cu3O7-δ, are reported. In addition, the translational energy distributions of Y, Y+, Ba, Ba+, and Cu are reported. Measurements made at low and high fluences on YO indicate that there are very large differences in the]] temperatures" inferred between the translational and the vibrational/rotational energy channels, implying that energy is partitioned in a very nonequilibrium fashion in the expanding plume. A measurement of the rotational and vibrational temperatures shows that the internal degrees of freedom are equilibrated in the expansion plume (Boltzmann distributions) with a temperature of approximately 1000 K being observed at normal processing fluences. The translational energy distributions of YO are observed to fit a shifted Boltzmann distribution at high fluences. The atomic species monitored all display non-Boltzmann velocity distributions at high fluences. The peak of the observed velocity distributions corresponds to energies as high as 10 eV for the YO neutral diatomic and up to several hundred eV for Ba+ at ablation fluences of 5 J/cm2. Bimodal velocity distributions are observed for the Cu, Ba, and Y neutral atoms at high incident fluences, implying ion-electron recombination as a partial source of the high neutral velocities.