Field-emission liquid-metal ion source and triode ion gun

Abstract

A pointed-filament-type field-emission liquid-metal ion source is designed and employed as a gold ion source. By adding a crossbar across a hairpin bend, the amount of the gold adhering on the filament is increased. The lifetime is estimated to be over 200 h at 10-μA emission current. The emission current increases with increasing extraction voltage up to a saturation value which is ascribed to a limitation of the supply of liquid gold to the needle apex. The value of current density per unit solid angle is 30 μA/sr at a total current of 30 μA, which is of the same order as that obtained from a gallium ion source previously reported. Emission current fluctuations of a few tens of percent of the dc component are observed. In order to regulate the emission current and suppress current fluctuations, a bias electrode in addition to a counterelectrode is placed close to the needle apex. With such a triode structure, the emission current is regulated by a bias voltage of several hundred volts and stabilized to within 1% by means of feedback to the bias voltage of a current monitor output.