Experimental studies of oxygen incorporation during growth of Y-Ba-Cu-O films by pulsed laser deposition

The authors of this paper have grown thin films of YBa2Cu3O7-δ in an oxygen atmosphere by pulsed-laser deposition using two synchronized lasers, separated by a variable delay (1μs--10 ms). The ablated fragments from the first laser leads to the formation of a blast wave in O2, leaving behind a rarefied ambient. If the second laser is triggered before the O2 pressure returns to equilibrium, the resulting films show a decrease in transition temperature with an expanded c-lattice parameter caused by defects in the non-chain sites of YBa2Cu3O7-δ. This demonstrates that a sufficiently high concentration of oxygen is needed during the time period that the fragments travel and deposit on the substrate. Based on the above understanding, we have been able to grow YBa2Cu3O7-δ films in a low pressure background (10-4--10-3 Torr) by using a pulsed, high intensity, jet of O2. The oxygen source is provided by a pulsed molecular beam value, and the opening of the valve and the triggering of the laser are synchronized with appropriate delay so that the supersonic gas jet and the ablated fragments arrive at the substrate at the same time. This provides the necessary oxygen to form the YBCO phase while maintaining a low oxygen background. The YBCO phase is not formed if the oxygen pulse is provided either before or after the arrival of the ablation fragments at the substrate. The ability to grow superconducting films at low background pressures should allow usage of in situ analysis techniques, such as reflection high-energy electron diffraction, during pulsed laser deposition