COMBINED FIELD ION AND FIELD ELECTRON EMISSION MICROSCOPY AND ENERGY-RESOLVED ATOM-PROBE SPECTROSCOPY OF Y Ba₂ Cu₃ O_7-x

Abstract
Field electron emission patterns of Y Ba₂ Cu₃ O_7-x, obtained under UHV conditions (<1·10^-10 Torr), between 78 K and 200 K are spatially correlated with features observed by argon-FIM at surfaces prepared by field evaporation. Fowler-Nordheim plots of local and total i-V data taken at 78 K, i.e. 14 K below T_c, display a straight-line behavior, at least up to total electron currents of 10 nA. Increasing the tip-temperature from 78 K to 150 K has no measurable effect on the local field electron emission current, which originates from the vicinity of a prominent facet identified as a region of enhanced emission. Above 150 K, an increase of the field electron emission current is measured, involving a hysteresis-like behavior as the temperature it decreased. Retarding-potential analysis of ⁴⁰Ar⁺ reveals a shift to larger energy deficits with increasing argon pressure, ranging between 5 eV and 10 eV above the energy deficit measured for W. This result possibly indicates a considerable penetration of the applied electric field into the near-surface layers under Ar-FIM conditions at 78 K.