Published online by Cambridge University Press: 10 February 2011
We have implemented coherent gradient sensing (CGS) to measure in situ, curvature and changes in curvature induced by temperature and O2 flow on thin film YBCO on MgO (001) substrates. CGS is a novel, real-time, full-field optical technique that provides a direct map of the components of the curvature tensor across the entire surface of the wafer. We have examined a well-characterized,700 nm thick YBCO film on a square 1”× 0.5mm MgO substrate with increasing temperature from 25 to 760°C and find the curvature increasing with temperature, although not always spatially uniform. By Stoney's equation, we relate the observed curvature to the thermal mismatch of the film and substrate where the maximum observed stress in orthogonal sample orientations is 1.2 and 1.4 GPa. For wafers under varying oxygen partial pressures, we observe dramatic local changes in the CGS interferograms, which we relate to the tetragonal to orthorhombic phase transformation YBCO exhibits as it cools in oxygen.