Determination of the negative ion yield of copper sputtered by cesium ions

Abstract

This paper describes the determination of secondary ion yields for negative ions obtained by bombardment of copper by cesium ions. Stable and reproducible surface conditions are reached by high rate sodium deposition simultaneously with sputtering. An optimum thickness of sodium corresponding to about one monolayer is found. Total negative ion yields K ⁻ _Σ are measured by a double modulation technique. Individual negative ion yields K ⁻ _i are then found by mass spectrometrically determining the various negative ion intensities, the sum of which relates linearly to K ⁻ _Σ. This method is based on the assumption of an equal angular and energy distribution of all sputtered negative ions. Data are given for K⁻ _Σ and K ⁻ _Cu and K⁻ _O. The dependence of K ⁻ _i on primary ion energy (500 to 2500 eV) is similar to ordinary sputtering which points to the same basic mechanism in both cases.