Thermionic oxide sources of Al+, Ga+, In+, and Tl+

Abstract

Oxides (Al2O3, Ga2O3, In2O3, and Tl2O3) of Group IIIA metals were coated on tungsten filaments to form thermionic emitters of purely ground state Al+, Ga+, In+ and Tl+ ions respectively. Variations of total ion emission current and ion purity with source filament temperature, and with time were studied. A very pure (99.9%) source of Al+(1 S0) could be obtained from the Al2O3-coated filament when heated to 2200°C but the filament was short lived. A stable ion current and a purity between 92% and 96% of Al+ could be produced at a lower temperature of 2000°C after 100 min of heating. At 1900°C, the Ga2O3-coated filament could produce Ga+(1S0) ions of 98% purity but its ion current was unstable with time. However, in the lower range of 1600-1820°C, a more stable Ga+ ion current of about 80% purity could be obtained shortly after heating. For the In2O3-coated filament, the purity of In+(1S0) ions reached a maximum of 90% at 1580°C while the total ion current increased to a maximum of 2900 nA at 1690°C. A very stable In+ ion current could be obtained at 1580°C. The Tl2O3-coated filament using tungsten or tantalum wires was found to be unsuitable as a source of Tl+ ions. © 1995.