Peter A. Duine

Optical switches based on magnesium lanthanide alloy hydrides

It is shown that thin layers of palladium coated magnesium lanthanide alloys reversibly go through an optical transition by variation of the hydrogen concentration, just as has recently been shown for pure lanthanides. With these layers optical switches can be constructed that exhibit three different optical states: a color-neutral transparent state at high hydrogen concentration, a nontransparent dark absorbing state at intermediate hydrogen pressures, and a highly reflective metallic state at low hydrogen pressures. The ratio in transmission between the transparent state and the reflecting state is more than 1000.

A model system for scandate cathodes

In cathode-ray tubes, high current densities at relatively low operating temperatures can be achieved with dispenser cathodes containing scandium oxide. The surface structure and precise emission mechanism of the scandate cathode are not known. The surface layers of such a cathode consist of the four elements Sc, Ba, O, and W. We have studied Sc, Ba, and O overlayers and various combinations of these elements deposited on the W(001) surface, under ultrahigh vacuum conditions. We have performed in situ measurements of the work function changes accompanying the surface treatments, and correlate these with the observed surface structures. High resolution medium-energy ion scattering was used to determine the compositional depth distributions and the geometrical structures at this model cathode surface. Auger electron spectroscopy peak height ratios show that W(001), with all three overlayer elements present, can be considered representative for real scandate cathodes. The observed ultra-low work function of the W(001)/Sc,Ba,O model system explains the high current densities on real scandate cathodes.

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

Abstract 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 Sc 2 O 3 . 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 CRTs.