Characterization of defect modes in YBa2Cu3O7−δ thin films probed by Raman scattering

A Raman analysis is performed on a series of fully oxygenated YBa2Cu3O7−δ thin films, on MgO(1 0 0) substrates, deposited by the pulsed laser technique at temperatures between 680 °C and 820 °C. θ − 2θ scans of the films by the X-ray diffraction show that the YBCO films are oriented in the c-axis. There are no extra peaks appearing in the X-ray diffraction data. Besides the well-known active modes, however, Raman spectra reveal a number of defect modes. The defect mode at 594 cm−1 redshifts and merges toward the O(4)-Ag mode at 502 cm−1 with decreasing deposition temperatures. This mode is significantly asymmetrical and broad, whereas the mode at 243 cm−1 is symmetrical, with a small full width at half maximum remaining unchanged at a value around its own frequency. The intensity of the mode at 243 cm−1 seems to depend on the intensity of the mode at 594 cm−1. Quantitative calculations concerning the relative intensities show that the two modes are related to each other.