COVARIANCE MAPPING OF CHARGED SPECIES EVOLUTION IN YBA2CU3O7-DELTA LASER-ABLATION

The composition and the evolution of the plume produced in the laser ablation of YBa2Cu3O7-delta targets have been investigated by applying the covariance mapping technique to the time-of-flight mass spectra of charged species. A spatial characterization of the plume both under high vacuum conditions (p = 10(-7) mbar) and in an O-2 environment (p = 9 x 10(-2) mbar) has been carried out. The first stage of YBa2Cu3O7-delta plume expansion has been found to be characterized by the formation of monatomic ions and simple oxide ions. In the plume evolution, the formation of large aggregates, though lighter than YBa2Cu3O7-delta is observed; they can be assumed to be intermediate products in the formation of the YBa2Cu3O7-delta structure. From a detailed analysis of the anti-correlation we have identified a path for the formation of YBa2Cu3O7-delta fragments. The effectiveness of the covariance mapping technique in the detection of reactions producing complex molecules, which can be considered as precursors of YBa2Cu3O7-delta, has been shown.