Characterization of ZrO2/Y2O3 laser ablation plasma in vacuum, oxygen, and argon environments

Laser ablation deposition of highly oriented yttria stabilized zirconia (YSZ) films is important for various technological applications and depends critically on the selection of background environment, with low pressure oxygen being the most common choice. Here, the spatial-temporal distribution of YSZ plume chemistry, excitation states, and energy was determined for ablations in vacuum, low pressure O-2, and low pressure Ar, using fluorescence analyses, element specific imaging techniques, and time-of-flight experiments. It was found that an Ar background considerably promotes excitation and ionization of zirconium during the first 1-3 mu s after the laser strike. There is much less zirconium excitation in an O-2 background, where a large fraction of atomic oxygen with a broad spatial distribution was found. ZrO and YO molecules were observed in both environments. Their highest concentrations were in the O-2 background, where fluorescence from these molecules near the substrate lasted for 2-5 mu s. Neutral species in YSZ plumes were fitted to Maxwellian type velocity distributions with a shifted center of mass. Kinetic energies derived from the fitted data were reduced by about a factor of 2 in Ar and O-2 backgrounds compared to in vacuum. This was not observed for Zr1+ species, which maintained about 100-120 eV mean kinetic energy nearly independently of the background. The ionization of Zr in the presence of Ar, the high velocity of ionized Zr atoms relative to the rest of the plume, the generation of molecular ZrO, YO, and atomic oxygen in the presence of O-2 are potentially important for chemistry and structure control of YSZ films. (C) 2000 American Institute of Physics. [S0021-8979(00)01014-8].