Optical properties and electronic transitions of zinc oxide, ferric oxide, cerium oxide, and samarium oxide in the ultraviolet and extreme ultraviolet

Abstract

Optical properties and electronic transitions of four oxides, namely zinc oxide, ferric oxide, cerium oxide, and samarium oxide, are determined in the ultraviolet and extreme ultraviolet by reflection electron energy loss spectroscopy using primary electron energies in the range 0.3-2.0 keV. This technique allows the evaluation of the optical response in these ultraviolet spectral regions of a thin layer of material, and the analysis is straightforward. It is performed within the dielectric response theory by means of the QUEELS-ε(k, ω)-REELS software developed by Tougaard and Yubero [Surf. Interface Anal.36, 824 (2004)SIANDQ0142-242110.1002/(ISSN)1096-9918]. The method consists basically in the fitting of experimentally determined single-scattering electron energy loss cross sections with a parametric energy loss function of the corresponding material, to the one calculated within a dielectric response formalism. The obtained refractive index and extinction coefficients, as well as the identified electronic transitions are compared, when available, with previously published results.

XPS primary excitation spectra of Zn 2p, Fe 2p, and Ce 3d from ZnO, α‐Fe2O3, and CeO2

“…All details about the sample preparation and the experimental set‐up are given in Pauly et al We just note here that the samples were irradiated with Mg K α X‐rays incident at an angle of 54° with respect to the surface normal and that the electrons are collected normal to the surface (except for CeO 2 for which the angle is 45°) with about 1‐eV energy resolution. Figure A‐C shows analysis by Equation of Zn 2 p photoemission spectra from ZnO, Fe 2 p from α‐Fe 2 O 3 , and Ce 3 d from CeO 2 , respectively, using the corresponding cross sections.…”

“…All details about the sample preparation and the experimental set-up are given in Pauly et al 14 To illustrate the impact of our approach, Figure 3 shows the primary spectra of the three samples obtained after subtraction of the inelastic background determined within three different procedures:…”

“…We note that the ELF of a given material can be obtained in different ways (from optical data, REELS measurements, or density functional theory calculations) . For the oxides considered here, we have used ELFs extracted from REELS spectra, published in Pauly et al Figure shows calculated for photoelectrons of 220‐, 540‐, and 370‐eV kinetic energy emitted from ZnO, α‐Fe 2 O 3 , and CeO 2 , respectively (these energies correspond to the particular photoelectron emissions studied here). is zero for energies below the band gap energy of the oxide.…”

“…We note that the ELF of a given material can be obtained in different ways (from optical data, REELS measurements, or density functional theory calculations). 11 For the oxides considered here, we have used ELFs extracted from REELS spectra, published in Pauly et al 14 Figure 1 shows K XPS sc calculated for photoelectrons of 220-, 540-, and 370-eV kinetic energy emitted from ZnO, -Fe 2 O 3 , and CeO 2 , respectively (these energies correspond to the particular photoelectron emissions FIGURE 1 Energy-differential inelastic-scattering cross section for X-ray photoelectron spectroscopy (XPS), K XPS sc of ZnO (with E = 220 eV), -Fe 2 O 3 (E = 540 eV), and CeO 2 (E = 370 eV) calculated with QUEELS-XPS for normal emission. The inset shows an expansion in the low energy loss region studied here).…”

Optical properties of molybdenum in the ultraviolet and extreme ultraviolet by reflection electron energy loss spectroscopy

“…In a recent paper [17], we applied this procedure to determine the optical constants of zinc oxide, ferric oxide, cerium oxide, and samarium oxide in the EUV and compared them with previous published data. Recently several new materials were proposed as components of EUV optics, as reflective layers, capping layers, etc., so there is an increasing interest for the evaluation of these properties [18].…”