Effect of oxygen in secondary ion mass spectrometry

About fifteen years have elapsed since the secondary ion mass spectrometer (SIMS) has been developed. However, it may be said that the spectrometers have not entered the practical working stage till Anderson employed O2+ and O- as primary ions. Secondary ion intensity increases and becomes stable even in the case of using Ar+ as the primary ions if the atmosphere is composed of oxygen. In the paper, first, the interaction of oxygen with solid surfaces and the secondary ion emission from the surface, and next, the secondary ion emission from the surface adsorbing oxygen are described. The interaction may be divided into four processes: adsorption and incorporation, desorption by sputtering, recoil implantation, and implantation. The effects of introducing oxygen into a SIMS are the upgrading of sensitivity (and accuracy), the reduction of relative sensitivity difference, the improvement of analysis in the direction of depth, the decrease of interfering lines due to compound ions, and the extension of application to quantitative analysis. Though there are many proposals to explain the mechanism of emitting secondary ions in a SIMS, unified explanation can not yet be obtained. For the mechanism of emitting secondary ions in which oxygen takes part, work function model, bond breaking model, band model, surface polarization model, etc. have been proposed so far. It is considered that the clarification of the mechanism of emitting secondary ions due to chemical process is specifically indispensable for the practical quantifying in a SIMS. (Wakatsuki, Y.)