Laser purification of metals (II); Purification of Ni and Ag

Abstract

We report on our effort in laser purification of metals and discuss the limitations of the method. Vaporized atoms are photoionized through a three-step excitation to the continuum above the ionization level and extracted by an electric field. The species so far tested are alloys of Ag and Ni. For purification of Ag, starting with an alloy system Ag 0.90In 0.10, we observed only a reduction of the In (Ag+In) atomic ratio of 0.10 in the vapor phase to 0.054. For Ni, using Ni 0.60Cu 0.40 as the starting material, we could reduce the Cu (Cu+Ni) atomic ratio of 0.63 in the vapor phase to 0.065 after laser purification. For both systems the main factor limiting the level of purification is considered to be a concomitant deposition of unionized impurity atoms that are scattered away from the atomic beam to the substrate.