Scanning Auger measurements of activated and sputter cleaned Re-coated scandate cathodes

The effect of sputtering and Sc supply rate for Re-coated scandate cathodes is investigated by scanning Auger measurements (SAM) and electron emission measurements. It is shown that during the first few hours of operation, the Sc supply rate is sufficiently high to recover from the ion bombardment. However, after several hours of operation the Sc supply rate is unmeasurably low and permanent damage shows up in the Sc intensity as well as in the electron emission current density. The current density of Re-coated scandate cathodes does not drop to the value of Re-coated cathodes without Sc2O3. It will be shown that this results from the roughness of the evaporated Re-surface which accounts for a reduced sputter efficiency. This offers the possibility of improving the performance of these cathodes in applications such as CRTʹs.