Investigations of superconducting and non-superconducting YBa2Cu3O/sub 7-x/ by field ion microscopy, atom-probe mass spectroscopy and field electron emission

The structure and composition of superconducting and non- superconducting samples of the YBa2Cu3O/sub 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 /approximately/ 0.35) contained a much larger molecular oxygen signal than mass spectra from the non-superconducting samples (x /approximately/ 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. 13 refs., 6 figs