Angular distributions of current density in liquid Ga-ion sources

Abstract

Current-voltage (I-V) characteristics and angular distribution of the current density of a liquid gallium ion source were investigated under various emitting tip temperatures and surface flow impedances. It is shown that the I-V slope is significantly influenced by the flow impedance of the liquid gallium on the emitting tip. The slopes of the I-V curve are shown to be steep for an emitting tip with a rough surface, and gentle for a smooth surface. The angular distribution of Ga ions was determined by measuring the current on metal rings concentric with the emission axis and located so as to form a portion of a hemisphere. The current density was found to be depressed near the center compared to the surrounding region. This density distribution persists for various axial locations of the rings. Moreover, the angular profile of current density at fixed axial locations is found to be identical for the same amount of emission current, irrespective of the tip-surface condition or the applied voltage. It shows that the amount of emission current has a strong correlation with the surface shape of the ion emitting Ga-liquid.

Beam Stability Improvement of a Liquid Metal Ion Source

“…Similar tendencies were observed in a previous report. 10) Figure 6 is a measurement of the beam stability. It is observed that the beam emission is quite stable; I rms =I avg is less than 1.8% for 4000 s. This (new model) stability is much better than that of the existing structure (old model, Fig.…”

“…The slope of the I-V characteristic curve is critically affected by the smoothness of the tungsten emission surface, i.e., the surface impedance. 10) If the resistance is too small, then the protrusion surface does not form properly, which may cause the beam to be unstable. The pointing procedure, prior to the blunting, etches the wire end acutely.…”