MASS SPECTROSCOPIC STUDIES ON OUTGROWTH PRECIPITATES IN LASER-ABLATEDFILMS

We have observed the velocity distribution of ionic species in the plu me by a mass spectrometer during laser ablation of Y1Ba2Cu3Ox target. The velocity distribution of Cu+ ions is strongly influenced by ambien t oxygen pressure. As an oxygen pressure is raised, the velocity distr ibution of Cu+ ions becomes narrows up to 2x10(-2) Torr, and then beco mes broad again at higher pressures. This change in the velocity distr ibution reflects the conversion of the supersonic expansion into the t hermal equilibrium flow of the ejected species in the plume. The surfa ce morphology of films is crucially dependent on the velocity distribu tions.