Calculation of overlayer thickness on curved surfaces based on XPS intensities

Accurate determination of overlayer thickness on samples with curved surfaces is of growing importance, especially in connection with nanometric materials systems. In this work two simple geometries are treated; closely packed spheres, well representing powder samples, and close-packed cylinders, modelling fibrous samples. In the case of the powder samples (the arrangement is similar to the structure of the closest packed spheres) in addition to the intensity originating from curved layers of the top row of the spheres, the contribution of the partially visible spheres of the second and third rows below the top row are also considered, enhancing the accuracy of the calculations. As is shown, the method of calculation for spheres and cylinders is similar but the values of the geometry correction factors are different. The applicability of the derived geometry correction factors, based on pure geometrical considerations, is supported with experimental data obtained in two material systems: the thickness of oxide and carbonaceous contaminant layers on Si3N4 powder and Al foil were determined. These types of calculations were conveniently performed by the XPS MultiQuant program providing not only the geometry correction factors but also other parameters, such as cross-sections, asymmetry parameters, etc. Copyright (C) 2004 John Wiley Sons, Ltd.