Impregnated-electrode-type liquid metal ion source

Abstract

The impregnated-electrode-type liquid metal ion source has a porous tip structure formed by sintering a refractory metal. The liquid metal flow rate is thereby positively controlled, and stable operation with a high current of 200–400 μA or alternatively with a low current, high brightness ion beam is possible. The ratio of liquid metal surface area facing vacuum to liquid volume is low, decreasing useless thermal evaporation of neutrals. The limitation on metal vapour pressure has been reduced by a large margin. The maximum vapour pressure for metals at the melting point for this ion source was 0.1–1 torr, which is higher by 2–3 orders of magnitude than that for the needle type. Some tens of metal elements can now in principle be ionized. Moreover, the number of usable metals is increased when the ion source is operated with alloys. By using a specially-designed double lens system, 20–40 μA of ion current could be transported a distance of 0.4–1 m within an optical column 2 cm in diameter. Therefore, this type of ion source is suitable not only for microfocusing applications but also for general use as a metal ion source.