Recovery treatment of EuBa2Cu3O7-delta thin films with activated oxygen plasma

Using high-duality c-axis-oriented EuBa2Cu3O7-delta (EBCO) thin;films with transition temperatures (T-ce) of about 90 K, a deterioration treatment by removal of oxygen atoms and a recovery treatment were performed in a sputte ring chamber: The removal of oxygen atoms by heating in a mixture gas of Ar + 7.5%O-2 at 7 Pa resulted in an expansion of lattice constants ten) of ab out 11.86A and semiconductive features. Two recovery methods using pure oxy gen and activated oxygen plasma were examined. For the treatment with pure oxygen, signs of recovery in structural and transport properties appeal cd at annealing temperatures (T-sa) above 300 degrees C at an oxygen pressure (Po-2(a)) of 30 Pa, but the as-grown state was not obtained even at Po-2(a = 2000 Pa. For the activated oxygen plasma treatment, where the deteriorate d films were exposed to oxygen plasma and oxygen gas was subsequently intro duced into the chamber, an almost complete recovery of superconducting and structural properties was achieved. The appropriate conditions fur the reco very were T-sa's of 500-700 degrees C, plasma exposure time (t(p)) above 30 min, and oxygen partial pressures (Po-2(a)) above 200 Pa. Atomic force mic roscope (AFM) images of EBCO films treated at T-sa's below 550 degrees C sh owed the same spiral structure as those of as-grown films. The image-deform ation and growth of outgrowths became obvious with increasing annealing tem perature. The change in the surface morphology revealed the substantial mov ement of constituent atoms from T-sa's of about 600 degrees C. Because the films exhibit optimum superconducting properties in spite of the rapid cool ing, it is considered that the movement of constituent atoms induces trilay ered perovskite structures with an excess oxygen atom deficiency at high te mperatures.