Micro-Raman study of ultra-thin YBa2Cu3O7-δ/YSZ films

Abstract

Micro-Raman scattering measurements of ultra-thin YBa2Cu3O7-δ (YBCO) films of various thicknesses, deposited by pulsed laser ablation on the yttrium-stabilized-zirconia (YSZ) (001) substrates, were carried out. The frequency of the O(4)-Ag mode shows a more marked increase with decrease in film thfckness than the O(2,3)-B1g mode does. The main contribution to the intensity of the O(2,3)-B1g mode is shown to be from the c-axis oriented grains and that of the O(4)-Ag mode comes from the a-axis oriented grains. Raman evidence for the formation of the BaZrO3 (BZO) transitional layer at the film interface was found, and the frequency changes of the O(4)-Ag and O(2,3)-B1g modes are explained in terms of lattice mismatch between YBCO and BZO at the interface. The large frequency increase of the O(4)-Ag mode with decreasing film thickness is due to the large mismatch between the Cu(2)-Cu(2) separation and the length of one unit cell of BZO, despite the good match between one unit cell of YBCO and three unit cells of BZO for the a-axis oriented grains.