Surface Science 129 (1983) 355-365 North-Holland Publishing Company 355 zyxwvutsr CONCENTRATION DEPTH PROFILES BY XPS; A NEW APPROACH zyxwvutsrqpon S. TOUGAARD Fysisk Institut, Odense Universitet, DK - 5230 Odense M, Denmark and A. IGNATIEV Department zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Physics, University of Houston, Houston, Texas 77004, USA Received 5 January 1983; accepted for publication 14 March 1983 A new technique is proposed to extract quantitative depth information from a single XPS spectrum. The technique has the advantages over existing methods of being non-destructive, simple and extremely fast. Depending on the system studied alternative methods may, however, give more detailed information. A quantity is defined, which for homogeneous samples is independent of the rate of generation of photoelectrons as well as of the peak shape, but which for inhomogeneous samples, due to elastic and inelastic electron scattering, is a strong function of the depth composition. This quantity D, which is essentially the ratio of the XPS peak area to the increase in background signal associated with the peak, is studied experimentally and theoretically. Through an analysis of eighteen XPS peaks from seven homogeneous polycrystalline metals, D is found to be a weak function of both the XPS peak energy and the metal. The experimental points scatter less than 25% around the mean value Do = 23 eV. Thus, for homogeneous solids, D is to first order matrix, concentration, and energy independent, i.e. it is a “universal” constant. As a consequence, by measuring this ratio for a given XPS peak, quantitative information on the depth location of the corresponding element can be obtained. The technique is demonstrated for a system where the depth composition is known in advance. This system consists of a submonolayer of Ag situated at varying depth underneath the surface of an Al sample. 1. Introduction Much effort is spent in the investigation of the depth distribution of elements near solid surfaces. Both in basic research and in technology (e.g. adsorption, reactions at surfaces, thin-film technology, adhesion, corrosion, catalysis, implantation and diffusion) knowledge of the chemical composition of the surface region of the solid is highly important. In the investigation of this the most popular techniques are [l] X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), ion scattering spectroscopy (ISS), secondary ion mass spectroscopy (SIMS) and Rutherford backscattering (RBS). 0039-6028/83/0000-0000/03.00 Q 1983 North-Holland