Method and apparatus for the elemental analysis of solids

Abstract

A method has been devised whereby material is removed from a solid surface and ionized to produce singly charged monatomic ions representative of the surface. A sample of the material (or surface) is mounted in place of the repeller electrode of an ion source, biased negatively with respect to the source's block and sputtered with argon ions. Some of the sputtered sample material is ionized by charge exchange with the argon ions near the ion source's exit slit and accelerated into a mass analyzer. An electron beam is used to ionize the argon sputtering gas. This method provides an advantage in that the initial kinetic energy spread of the monatomic ions is much lower than with other methods. To perform this method, the solid sample is mounted upon a removable probe which is introduced into the ion source or ion chamber of a mass spectrometer. More specifically, the sample is placed in a recessed cavity in the end of the probe located opposite the exit slit of the ion chamber. In this manner, the non-conductive walls of the probe aid in directing the argon ions perpendicularly onto the surface of the solid sample, thereby increasing the yield of ions which pass through the exit slit.