SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 2002; 34: 201–205 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/sia.1283 Determination of surface nanostructure from analysis of electron plasmon losses in XPS F. Yubero, * J. P. Holgado, A. Barranco and A. R. Gonz ´ alez-Elipe Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), Av. Am ´ erico Vespucio, s/n E-41092 Sevilla, Spain Received 16 July 2001; Revised 23 October 2001; Accepted 24 December 2001 We have explored the possibility of obtaining information about the surface nanostructure (i.e., how a given phase of material is distributed near to the surface region) from the analysis of loss plasmons that appear in the lower kinetic energy side of photoelectron and Auger peaks. First, we show an example where information is mainly obtained from the position of the plasmon peak. In practice, two-dimensional growth of an Al 2 O 3 deposit on SiO 2 is deduced by identification of surface plasmon excitation due to electron transport of the corresponding Al KLL signal. Furthermore, a new method based on a quantitative (plasmon peak intensity) description of the single plasmon excitation that appears behind a photoelectron peak is proposed. This method has been applied to describe the growth mechanism of MgO deposited by evaporation on TiO 2 . Thus, it is shown that MgO grows with strong island formation according to the analysis. The consistency of the proposed method is supported by factor analysis of the loss structure behind the Mg 1s peak. Moreover, the validity of the proposed method has been checked using Tougaard background analysis for the same system. From these results, an alternative method, based on analysis of the plasmon structure observed behind x-ray photoelectron peaks, is proposed for characterization of the nanostructure in this type of system. Copyright  2002 John Wiley & Sons, Ltd. KEYWORDS: XPS; surface plasmons; bulk plasmons; growth mode INTRODUCTION Two types of information are available through analysis of solid surfaces with x-ray photoelectron spectroscopy (XPS). 1 First elemental composition and distribution within the out- most 5–10 nm of material is related to the intensities of the main XPS peaks and the electron inelastic backgrounds gen- erated by electron transport. Second chemical information is accessible regarding the atoms present at the surface by considering peak positions and the fine structure appearing in the vicinity of the main peaks. Note that these argu- ments are also applicable to x-ray-induced Auger electron spectroscopy (XAES). This paper deals with the first type of information, in particular with the identification of the first stages of growth of thin films. In-depth profile information on the first 5–10 nm of material can be obtained not only from the intensity of the main zero-loss peaks but also from the inelastic background that appears at the lower kinetic energy side of the photoelectron peaks. Tougaard 2–5 has explored this idea to develop models that correlate the shape of photoelectron peaks (elastic peak C background) with the in-depth profile that generates them. The origin of the inelastic background in XPS/XAES is electron transport. When an electron is transported within L Correspondence to: F. Yubero, Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), Av. Am´ erico Vespucio, s/n E-41092 Sevilla, Spain. E-mail: yubero@cica.es a solid it interacts with the electrons of the medium and, as a consequence, plasmons are excited. 6 Electronic plasmon excitations are usually studied by reflection elec- tron energy-loss spectroscopy (REELS). However, elec- tron transport is a common feature in XPS, XAES and REELS. The actual energy-loss distribution due to plasmon excitations for electrons moving in a solid depends on the band structure of the material where the interaction takes place, the energy and the trajectory of the moving electron. 7,8 These plasmon losses are usually described with a dielectric formalism. 6–8 The main function describing this energy distribution is the so-called electron energy- loss function (ELF), defined as Imf1/εg (‘Im’ denotes the imaginary part and ε is the dielectric function). The main feature in this function can be considered the most probable energy loss for electrons moving in the bulk of a material. On the contrary, surface losses for that material would be described by Imf1/⊲ε C 1⊳g. In practice, and in the case of oxide materials, bulk plasmon losses appear as broad features at 14–23 eV 9 energy loss, whereas surface plasmon distributions are quite similar in shape but with the main peaks are shifted a few electron-volts to lower energy. In this paper, the use of simple criteria that may serve to identify the distribution of material within a solid surface by XPS or XAES measurements is highlighted. Several examples are shown where identification of the plasmon position with respect to a main peak, or the relative intensity of a plasmon Copyright  2002 John Wiley & Sons, Ltd.