Peter Dr. Geittner

Emission properties of top-layer scandate cathodes prepared by LAD

Abstract In the first part an overview of scandate cathode types, their historical development and the current status of research is given. Then recent improvements obtained by our group are elucidated: A new type of top-layer scandate cathode has been prepared with the aid of laser ablation deposition. Emission current characteristics have been measured as a function of voltage and temperature. Zero field emission i10% is determined as 10% deviation from space-charge law. At 965°CMo-Br i10% of about 400 A/cm2 and at 760°CMo-Br of 32 A/cm2 were achieved, which is more than a factor of 3 higher than the best values for other scandate type cathodes given in literature. It corresponds to a work-function of about 1.16 eV with a Richardson constant of 7.8 A cm−2 K−2. Other emission properties such as uniformity and cathode life are discussed. A description of I U characteristics via the superposition model is given.

Supply and loss mechanisms of Ba dispenser cathodes

Abstract Ba dispenser cathodes, especially W–I, Re–I, Os/Ru–I and Sc 2 O 3 /Re top-layer Scandate cathodes have been investigated with respect to Ba resupply, Ba evaporation and ion bombardment behaviour. Since a 411 impregnated base was used for all these types, the same Ba evaporation activation energy of 3.15 eV was found despite different surface coatings. These and further results are compared with literature data. From ion bombardment (=IB) investigations different sputter yields are derived. With respect to IB stress tests, dynamic shielding of the surface complex rest by Ba sitting on top is introduced, which allows the extrapolation of resistivity data to real tube conditions. Information about the Scandate surface complex is evaluated.

Dynamic shielding during ion bombardment of Ba dispenser cathodes

Abstract Ion bombardment (IB) resistivity is a key parameter for cathodes to be operated in TV tubes and CMTs over lifetimes of several years. Thus, accelerated stress tests with much higher ion dose rates than those present in real tube environment are normally used. Here, IB resistivity of Os/Ru-I and top layer Scandate cathodes was investigated. It was observed by variation of the dose rates, that Ba resupply modified the survived ion dose and led to a dynamic shielding of the rest of the surface complex/dipole below Ba. Enhanced IB resistivity w.r.t. total ion dose was observed for reduced ion dose rates. Based on a model of shielding an extrapolation from stress tests to real tube conditions has been established, where the correction factor is in the range of 1–8, depending on the test conditions.