Liquid metal microdroplet source for deposition purposes

Abstract

The phenomenon of microdroplet emission in unstable regimes of liquid metal ion sources is studied. The spectrum of small droplets of the radius of 10 to 200 Å is shown to be of continuous character (microdroplet chaos), and that of larger ones to be discrete. Both the charge-to-mass ratio and the intensity of droplets as function of the current magnitude are measured. The generation of small droplets is shown to be caused by the development of the Rayleigh instability on the surface of jets ejected from the Taylor cone vertex. High- and low-frequency oscillations of the electric field develop on the jet apex in the process of emission of small droplets. These oscillations cause the liquid pressure modulation and lead to the parametric excitation of capillary waves (Faraday effect) on the surface of the Taylor cone. The crests of the capillary relief serve as an additional generator of droplets. The parameters of droplets (radius, charge, intensity) are calculated along the frequency of low-frequency oscillations of the ion current. The calculations are in agreement with the measured values of these quantities. The experiments were carried out in the tin source using a Wien mass-analyzer and a transmission electron microscope. The results may have a practical interest for deposition of different kinds of coatings.