Characterization of the Electronic Structure and Optical Properties of Al 2 O 3 , ZrO 2 and SrTiO 3 from Analysis of Ref
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Characterization of the Electronic Structure and Optical Properties of Al2O3, ZrO2 and SrTiO3 from Analysis of Reflection Electron Energy Loss Spectroscopy in the Valence Region G. L. Tan1), L. K. Denoyer2), R. H. French1, 3), A. Ramos4), M. Gautier-Soyer5), Y. M. Chiang4) 1) 2) 3) 4) 5)
University of Pennsylvania, Materials Science Dept. 3231 Walnut St. Philadelphia, PA 19104, USA Deconvolution and Entropy Consulting, 755 Snyder Hill, Ithaca NY 14850, USA DuPont Corporation Central Research, E356-384, Exp. St., Wilmington, Delaware 19880-0356, USA. Dept. of Materials Science.& Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139USA
Service de Physique et Chimie des Surfaces et Interfaces, CEA Saclay, France.
Abstract Characterization of thin surficial films of oxides has become the focus of increased interest due to their applications in microelectronics. The ability to experimentally determine the electronic structure and optical properties of oxide materials permits the direct study of the interband transitions from the valence to the conduction band states. In the past years there has been much progress in the quantitative analysis of transmission electron energy loss spectroscopy (TEELS) in the electron microscope Here we employed reflection electron energy loss function (REELS) as well as vacuum ultraviolet (VUV) spectroscopy to determine the dielectric functions of oxide materials, i.e. Al2O3, ZrO2 and SrTiO3. The two main steps in the analysis are the removal of the effects of multiple scattering from the REELS spectra followed by application of the Kramers-Kronig dispersion transforms to the single scattering energy loss function to determine the conjugate optical variable and then the complex dielectric function. The surface and bulk plasma resonance spectra for these oxide materials have been determined from VUV and REELS, along with the influence of primary electron energy on the REELS results. The relative contribution of surface and bulk plasmon oscillation in REELS has been investigated. Comparison with VUV results and existing TEELS results indicate that Kramers-Kronig analysis can also be applied to REELS spectra and the corresponding conjugate optical properties can be obtained. Quantitative studies of the electronic structure and optical properties of thin surficial films using VUV and REELS or TEELS, represent a new avenue to determine the properties of these increasingly important films.
1. Physical basis of REELS Reflection electron energy loss spectroscopy (REELS) consists in bombarding the surface of a sample with a beam of monoenergetic electrons and detecting the energy distribution of the backscattered electrons.1 The REELS spectrum consists of two regions: first the elastic peak is due to electrons that have lost no energy (elastic backscattering); the other structures, at lower kinetic energies, correspond to electrons that have lost part of their energy through electronic excitations or phonon excitations within the solid, as being shown in the Schematic o
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