SPOT-SIZE-DEPENDENT BIFURCATION OF LASER-ABLATED PLUMES

An ion probe investigation of an excimer-laser-ablated plume from a high-ir, superconducting YBa2Cu3O7-x (YBCO) target in an oxygen ambient revealed a significant alteration of the propagating plume as the laser spot size on the target was changed. For larger spot sizes, the time-resolved ion signals showed a bifurcation of the laser plume into two distinct components with increasing spot size. The faster component of the plume showed free expansion behavior, while the slow component corresponded to a highly collisional regime that represented the onset of a shock wave. Similar plume characteristics have been seen for laser-generated plumes expanding in high-pressure ambient gases. The YBa2Cu3O7-x films grown under the conditions that produced a high degree of plume bifurcation yielded high-quality superconducting films. Implications of these findings toward superconducting film growth are discussed. (C) 1995 American Institute of Physics.