SURFACE AND INTERFACE ANALYSIS, VOL. zyxwvuts 19, 205-210 zyxwvuts (1992) Composition of Oxides and Nitrides from Line Shapes of Metal Core Level X-ray Photoelectron Spectra zyxw L. Galan, P. Prieto, C. Morant, L. Soriano, J. M. Sanz, E. Elizalde and F. zyxw Rueda Departamento de Fisica Aplicada C-XII, Universidad Aut6noma de Madrid, E-28049 Madrid, Spain A method is proposed which evaluates the averaged composition of a sample in terms of the centroid of the core level XP spectrum. The method is based on the basic principle of electron spectroscopy for chemical analysis, i.e. the additive property of the chemical shifts and their proportionality to the ligaod co-ordinatioa It allows one to calculate the averaged composition of compounds if the line shapes of spectra corresponding to stoichiometric samples (including the pure metal) are known and a few simple conditions are assumed. The main advantage of this method is that the composition can be obtained even if the individual contributions of the =rent oxidation states cannot be resolved or deconvoluted, so that no previous knowledge of the oxidation states or coordination structure is necessary. This method of calculating the composition is illustrated by its application to ZrO, zyx , HfO,, NbN, , TaN,O, and SiN,O, obtained by different methods. The results are tben compared with those obtained from the usual XPS quantitative analysis, so that further insight to the sample near-surface structure and composition can be gained by this combined study. INTRODUCTION The determination of the averaged composition of a non-stoichiometric sample is a normal problem in quantitative XPS. In the case of substoichiometric compounds MX, where several oxidation states or cation-anion co- ordinations are present (e.g. suboxides, subnitrides, etc.), the most usual approach to estimate the averaged com- position x consists of the use of'-3 i=O where zyxwvutsrqp m and zyxwvuts n are the co-ordination numbers of the cation and anion respectively according to a stoichio- metric compound of the type M,X, and Z(Mi+)is the intensity of the corresponding contributions of the dif- ferent oxidation states. The averaged composition can be obtained from Eqn (1) if m/n (i.e. the cation-anion co-ordination) is known and the XP spectrum has been conveniently deconvol- uted into the corresponding components (i = 1, . .. , m). However, very often the number of shifted core levels to be used in the fitting procedure appears ambiguous and thus so does the result. Alternatively, the averaged composition can be deter- mined in terms of the total intensity of the respective XP spectra: I(XUS(X) . I. . I = Z(M)/S(M) where S refers to the corresponding sensitivity factors. However, Eqn (2) can result in an overestimation of x when compared with &hem owing to the existence of adsorbed X which does not bond to M to form the compound. In this case the adsorbed X contributes to the intensity of X but not to Z(M'+). In this work we propose an extension of Eqn (1) to evaluate the averaged composition xChcm on the basis of an overall peak shape analysis of the spectra of the core levels. The composition can be determined even if the individual contributions of the different oxidation states, Z(Mi+),cannot be resolved or deconvoluted, so that no previous knowledge of the oxidation states or co-ordination structure is necessary. The method is illustrated by its application to ZrO,, HfO, , NbN, , TaN,O, and SiN,O, obtained by differ- ent methods and the results are compared with those resulting from the use of the intensity ratio [Eqn (2)]. METHOD OF ANALYSIS The method proposed in this work is a simple gener- alization of Eqn (l), eluding the process of deconvolu- tion of the spectrum into its components. The generalization is based on the use of the centroid of the spectrum, 1 N(E)E dE E, = (3) Ol42-2421/92/240205-06 S38.00 zyxwvutsrqpon 0 1992 by John Wiley & Sons, Ltd.