INVESTIGATIONS OF SUPERCONDUCTING AND NON-SUPERCONDUCTING YBa₂ Cu₃ O_7-x BY FIELD ION MICROSCOPY, ATOM-PROBE MASS SPECTROSCOPY AND FIELD ELECTRON EMISSION

Abstract
The structure and composition of superconducting and non-superconducting samples of YBa₂Cu₃O_7-x were examined by field ion microscopy, atom-probe mass spectroscopy and field-electron emission techniques. Field ion microscope images from both types of material exhibited ring structures associated with atomic or multiatomic layers and uniform, layer-by-layer field evaporation was possible. Atom-probe mass spectra contained signals corresponding to atomic and molecular oxygen, all three metals, and oxides of Cu and Y. Atom-probe mass spectra from the superconducting samples (x~0.35) contained a much larger molecular oxygen signal than mass spectra from the non-superconducting samples (x~0.8) indicating that oxygen in the CuO chains is field desorbed preferentially as molecular oxygen ions. Field electron emission from the superconducting samples exhibited normal Fowler-Nordheim characteristics above and below the superconducting transition temperature. Surface contaminates were found to decrease the work function of the material by as much as 39%. With the exception of one isolated experiment, no significant temperature effect on the field emission characteristics were observed.