Determination of amount of substance for nanometre thin deposits: Consistency between XPS, RBS and XRF quantification

Abstract

Quantification on the nanometre scale is a key task in quality control and for the development of new materials in nanotechnology. In this paper we have studied the consistency in the determination of the amount of substance found by XFS peak shape analysis, Rutherford backscattering spectroscopy (RBS) and x-ray fluorescence spectrometry (XRF). To this end, ZnO was deposited by plasma-enhanced chemical vapour deposition on the three substrates. Four different sets of samples were produced, with the amount of ZnO deposited in the range 1-10 nm. From XPS analysis it is found that ZnO grows in the form of islands on all three substrates. For each system, the analysis was done independently with two XPS peaks from the overlayer with widely different kinetic energy and one XPS peak from the substrate. The growth mechanism found from analysis of each of the three peaks was consistent and the total amount of determined ZnO material was identical to within 15%. The root-mean-square deviation from the XPS quantification of the relative AOS was 20% for XRF and 16% for RBS. Because the absolute amount of substance determined from analysis of the three XPS peaks for each sample was consistent, it is concluded that the energy dependence of the applied inelastic mean free paths (taken here from the empirical TPP-2M formula) is correct. It was found that the absolute amounts of substance determined by RBS and XRF are consistently factors of 2.1 and 1.5 lower than the that determined by XPS peak shape analysis. It is suggested that the main reason for this large discrepancy is inaccuracy in the applied 'effective' inelastic electron mean free path. Copyright © 2003 John Wiley & Sons, Ltd.