The determination of composition depth profiles using spherical erosion and scanning Auger electron spectroscopy

Abstract

Accurate composition depth profiles which are essential to many investigations of surface coating and surface treatment processes are at present obtained by sequential ion bombardment and surface analysis. Successive layer removal by ion bombardment is satisfactory when the depth of interest is less than 1 μm; above this it is time consuming and induces surface damage which causes problems of interpretation. This paper describes an accurate method of depth profiling which does not rely on ion bombardment. A very fine taper section of the specimen surface regions is produced by the erosion of a hemispherical crater with a spherical tool. Scanning Auger electron spectroscopy is then used to conduct analysis across this taper face. Initially, line scans to detect the elements of interest are performed across the diameter of the crater; these are followed by individual point analyses at the major places of interest for purposes of quantification. A linear depth profile is then derived using the crater dimensions and simple geometry. This method of depth profiling is rapid because it eliminates ion bombardment; it is also non-destructive and applicable to all types of materials. Further, it completely avoids the uncertainties of interpretation which arise from depth resolution degradation caused by the differential sputtering of elements during long term ion bombardment. A composition depth profile through a TiN coating on steel is used to illustrate the method.