Raman scattering as a contactless room-temperature test of the quality of YBa2Cu3O7-x thin films

The room-temperature Raman spectrum of YBa2Cu3O7−x is sensitive both to stoichiometry and to the transition from the semiconducting to the superconducting state as a function of oxygen annealing. In particular, it is shown that a good quality film with a Tc of ∼90 K and a sharp resistivity transition has not been produced if the frequency of the O(1) stretch along the c axis shifts from 500 cm−1 to lower frequencies. In this paper, two types of processing failures are illustrated: (1) lack of sufficient oxygen and (2) incorrect stoichiometry. No attempt has been made to predict Tc from the Raman data for less than optimum films.