Observation of two distinct components during pulsed laser deposition of high <i>T</i> <i>c</i> superconducting films

Abstract

Using Rutherford backscattering technique, we have measured the angular distribution of the composition and thickness of the Y-Ba-Cu oxide film deposited by firing excimer laser (30 ns, 248 nm) pulses at a stoichiometric Y1Ba2Cu3O7−x pellet. The angular distribution consisted of two distinct components: one a cos θ component, a result of evaporation, and the other a highly forward directed component, a result of a secondary ejection process. The evaporated component is nonstoichiometric, as one would expect, whereas the forward-directed component has a composition close to that of the pellet. Further, the forward-directed stoichiometric component increases with the laser energy density in comparison with the evaporated component. These observations are discussed in the context of current models of laser-induced material ejection at surfaces.The laser energy dependence of the deposition is of critical importance in controlling the film stoichiometry.