Structural variation of the interface-engineered layers in YBa2Cu3O7-deltathin films

The atomic structures of interface-engineered YBa2Cu3O7-delta (YBCO)/plasma -treated Y-BCO/a-axis YBCO 'trilayer' samples have been observed by transmi ssion electron microscopy. The microstructures are compared by changing the plasma treatment conditions. The detailed structure of the interface or th e barrier layer varies both from sample to sample and from place to place i n the same sample. It is found that the interface structure depends on both the accelerating voltage and the atmosphere for the plasma treatment. The interfaces under high accelerating voltages (700 and 500 V) are strained, w hile strain-free barriers with different crystal structures are formed by t he treatment under lower accelerating voltages (350 and 200 V). In the samp le prepared in the mixed atmosphere of argon and oxygen, a kind of cubic st ructure is found at the interface, while in the sample fabricated in pure a rgon, besides the cubic structure, BaCuO2 and Y2O3 are also observed in the interface. (C) 2001 Elsevier Science B.V. All rights reserved.