Liquid metal ion source for cluster ions of metals and alloys: design and characteristics

Currently liquid metal ion sources (LMISs) are of great interest for a wide variety of applications—ion implantation, ion microlithography, thrusters for electric space propulsion, etc. A novel application of the LMIS is for the production of metallic cluster ions. In our laboratory we have designed and optimized the performance of a LMIS for the production of cluster ions of alkali metals. Using liquid rubidium (Rb) we have observed copious production of singly charged cluster ions (Rb+N, N=1–100). As expected the largest fraction of the emission consists of atomic ions. For low source current (<5 μA) about 80% of the total emission current is that of Rb+. The remaining 20% consists of Rb+2 and Rb+3. However, for large emission currents (>80 μA) we observe cluster ions as large as Rb+100. We study the mass distribution using the time-of-flight technique.