Optical Constants and Inelastic Electron-Scattering Data for 17 Elemental Metals

Abstract

Two new sets of optical data, i.e., values for the real (ε1) and imaginary (ε2) parts of the complex dielectric constant as well as the energy loss function (ELF) (Im{−1∕ε}), are presented for 16 elemental metals (Ti, V, Fe, Co, Ni, Cu, Zn, Mo, Pd, Ag, Ta, W, Pt, Au, Pb, and Bi) and 1 semimetal (Te) and are compared to available data in the literature. One data set is obtained from density functional theory (DFT) calculations and gives ε from the infrared to the soft x-ray range of wavelengths. The other set of optical constants, derived from experimental reflection electron energy-loss spectroscopy (REELS) spectra, provides reliable optical data from the near-ultraviolet to the soft x-ray regime. The two data sets exhibit very good mutual consistency and also, overall, compare well with optical data found in the literature, most of which were determined several decades ago. However, exceptions to this rule are also found in some instances, some of them systematic, where the DFT and REELS mutually agree significantly better than with literature data. The accuracy of the experimental data is estimated to be better than 10% for the ELF and ε2 as well as for ε1 for energies above 10eV. For energies below 10eV, the uncertainty in ε1 in the experimental data may exceed 100%, which is a consequence of the fact that energy-loss measurements mainly sample the absorptive part of the dielectric constant. Electron inelastic-scattering data, i.e., the differential inverse inelastic mean free path (IMFP) as well the differential and total surface excitation probabilities are derived from the experimental data. Furthermore, the total electron IMFP is calculated from the determined optical constants by employing linear response theory for energies between 200 and 3000eV. In the latter case, the consistency between the DFT and the REELS data is excellent (better than 5% for all considered elements over the entire energy range considered) and a very good agreement with earlier results is also obtained, except for a few cases for which the earlier optical data deviate significantly from those obtained here.