Measurement of optical constants of Si and SiO_2 from reflection electron energy loss spectra using factor analysis method

摘要

The energy loss functions (ELFs) and optical constants of Si and SiO_2 were obtained from quantitative analysis of reflection electron energy loss spectroscopy (REELS) by a new approach. In order to obtain the ELF, which is directly related to the optical constants, we measured series of angular and energy dependent REELS spectra for Si and SiO_2. The λ(E)K(ΔE) spectra, which are the product of the inelastic mean free path (IMFP) and the differential inverse IMFP, were obtained from the measured REELS spectra. We used the factor analysis (FA) method to analyze series of λ(E)K(ΔE) spectra for various emission angles at fixed primary beam energy to separate the surface-loss and bulk-loss components. The extracted bulk-loss components enable to obtain the ELFs of Si and SiO_2, which are checked by oscillator strength-sum and perfect-screening-sum rules. The real part of the reciprocal of the complex dielectric function was determined by Kramers-Kronig analysis of the ELFs. Subsequently, the optical constants of Si and SiO_2 were calculated. The resulting optical constants in terms of the refractive index and the extinction coefficient for Si and SiO_2 are in good agreement with Palik's reference data. The results demonstrate the general applicability of FA as an efficient method to obtain the bulk ELF and to determine the optical properties from REELS measurements.