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

The composition and the evolution of the plume produced in the laser a blation 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 h igh 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-d elta plume expansion has been found to be characterized by the formati on of monatomic ions and simple oxide ions. In the plume evolution, th e formation of large aggregates, though lighter than YBa2Cu3O7-delta i s observed; they can be assumed to be intermediate products in the for mation of the YBa2Cu3O7-delta structure. From a detailed analysis of t he anti-correlation we have identified a path for the formation of YBa 2Cu3O7-delta fragments. The effectiveness of the covariance mapping te chnique in the detection of reactions producing complex molecules, whi ch can be considered as precursors of YBa2Cu3O7-delta, has been shown.