Identification of Cluster Beam Constituents and Qualitative Descripton of Cluster Emission from Liquid Gold Ion Source

Abstract

ABSTRACTThe distribution of charged gold clusters and micro droplets emitted from liquid gold ion source as a function of charge to mass ratio has been investigated using three complementary techniques: transverse magnetic deflection, quadrupole mass spectrometry, and single particle detection scheme. The measurements have been made as a function of total beam current and angle of emission. The above three methods have some overlap range that was used for comparison and verification of data gathered by each technique. The magnetic deflection results indicate that for the source structure used in this study, clusters are present along the axis of the beam, over the entire current range under investigation. However, their relative abundance is significantly increased as total current is increased. The quadrupole data exhibits a broad peak which is centered around 104 Coul/Kg corresponding to a cluster of ≈ 1000 atoms charged to ≈20+. The position of the peak moves slightly toward lower mass (higher Q/m ratio) as the total beam current is increased. The biggest cluster detected so far using single particle detector has a charge to mass ratio of 17 Coulomb/Kg corresponding to a droplet of 108 Au atoms having a radius of ≈ 740Å atoms charged to ≈ 9000+. Several experimental observations point to the fact that cluster dominated emission mode might be qualitatively different from ion emission mode. Based on experimental observations a qualitative model for cluster emission is proposed.