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Successful attempts to establish quantum-mechanical transparency for tunneling electrons in YBaCuO and BiSrCaCuO surfaces are reported. Depending on surface pretreatments, field electron and field ion energy distributions were initially shifted by several electron volts, referenced to the Fermi level, EF, of the metal support. This behavior is probably caused by a voltage drop in a dielectric layer at the surface. With the polarity for field electron emission, an “activation” of this layer towards metallic properties was observed. Electron and ion energy distributions measured after activation displayed sharp cut-offs at EF, in agreement with recent photoemission and inverse photoemission results. Metallic-like (possibly superconducting) surfaces were created through electric-field induced “tear-off” of a collection of surface atomic layers. Different electronic densities of states above EF, appear to be responsible for peak structures found in the ion energy distributions from BiCaSrCuO specimens.
