AVS 47th International Symposium
    Material Characterization Tuesday Sessions
       Session MC-TuA

Paper MC-TuA6
Comparison of ISS, XPS, and QUASES-XPS Techniques for Determination of Growth Mechanisms: Application to Thin Iron Oxide Films Deposited on SiO2

Tuesday, October 3, 2000, 3:40 pm, Room 207

Session: Quantitative Surface Analysis
Presenter: F. Yubero, Inst. for Material Science of Sevilla
Authors: F. Yubero, Inst. for Material Science of Sevilla
A.R. Gonzalez-Elipe, Inst. for Material Science of Sevilla
S. Tougaard, University of Southern Denmark
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We have studied the formation of iron oxides on SiO2 under varying growth conditions by X-ray photoemission spectroscopy (XPS) and ion scattering spectroscopy (ISS). Three different procedures for quantitative analysis of the experimental data were used: 1) traditional analysis of the XPS-peak intensity by assuming a layer formation that covers the surface completely, 2) combination of the XPS-peak and ISS intensities assuming a Poisson distribution of island heights, and 3) Tougaard-method (QUASES@footnote 1@) to determine in-depth profiles from analysis of the peak and background. The difference between the three methods lies mainly in the a priori assumptions made on the surface morphology. In contrast to method 1) and 2), the Tougaard-method is free from assumptions about the growth structure of the overlayer. By a critical comparison of the results, it is concluded that the Tougaard-method gives the most complete and reliable information. It is found that iron oxides on SiO2 grow with strong island formation, whose height depends on the preparation conditions of the deposit. The growth mechanisms are proposed. Thus, for example, if iron oxide is deposited on SiO2 at room temperature in a PO2 of 2´10-6 mbar, islands of ~22@Ao@ homogeneous thickness are formed for surface coverages below 20%. If the samples are annealed at 773K in a PO2 ~4´10-5, higher islands are formed (~32 @Ao@). For iron oxide treated by a plasma of oxygen, ~40 @Ao@ tall islands are formed for surface coverages below 30%. Besides, even ~35 @Ao@ of iron oxide does not fully cover the SiO2 substrate surface. Strong shadowing effects are observed in the ISS signal from the iron oxide deposits on SiO2 due to the tall island formation. As expected, the shadowing effects are stronger when taller islands have been formed. @FootnoteText@ @footnote 1@ http://www.quases.com