Untersuchungen zur thermionischen Erzeugung von Alkali-Ionenstrahlen

The aim of this work was the investigation of the underlying processes of the thermionic generation of alkali-ions. Therefore, ion emitters based on a mixture of the emittermaterial MAlSi2O6 with M = K, Rb, Cs and a metal powder are used. This emitters had previously been developed in the group of Prof. Weitzel and can be used to obtain high purity ion beams with an ion current of about 100 nA. Using this type of emitter it was not possible to create a lithium or sodium ion beam from MAlSi2O6 with M = Li, Na. Furthermore, it is found that the obtained work functions are very different for each sample, despite the samples are created from the same batch of material. In filament emitters a metal foil is used as sample support and resistance heating device. The emitter material is molten on top of the filament without adding a metal powder as matrix. With this technique and by using emitter materials of the composition MAlSiO4 and MAlSi2O6 with M = Li, Na, K, Rb, Cs ion beams of lithium, sodium, potassium, rubidium and cesium are accessable. By studying the temperature- and fielddependence of the emission hte work function can be accessed, showing a clear structure dependence of the material. To investigate the influence of the anionic framework materials of the composition CsMSi2O6 and CsMGe2O6 with M = B, Al, Ga, F e are used. For all investigated samples the transition from space charge limited to field assisted emission is observed. By employing retarding field analyses the kinetic energy of the emitted ions is determined. For LiAlSi2O6 the observed emission characteristics show an excellent agreement with numerical simulations. Last but not least, the thermionic emission was used to measure the ionic work function for lithium from lithium-cobalt-oxide for the first time. The observed value of about 4 eV is in excellent agreement with a work function of 3.6 − 4.5 eV obtained from theoretical considerations.