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Retrieval of dielectric and structural properties of amorphous SiO2 nanopowder based on optical measurements and Bergman's spectral representation theory

The dielectric and structural properties of an amorphous SiO2 nanopowder have been characterized in the framework of Bergman's spectral representation. The methodology used in this paper is based on the acquisition of reflectivity spectra from a set of nanopowder pellets with different levels of porosity and the measurement of the transmittance spectra of KBr pellets containing low levels of silica nanoparticles. The fit of the spectra was performed with a dielectric function model through the solution of a nonlinear optimization problem including all the experimental data. In addition to the optical properties, the complete analysis also provided an accurate estimate of the total porosity of pellets and evaluated the percolation of the silica agglomerates in the porous matrix. A comparison with the predictions obtained by other mixing formulas clearly demonstrates that Bergman's theory is the most appropriate for treating this type of powder.The dielectric and structural properties of an amorphous SiO2 nanopowder have been characterized in the framework of Bergman's spectral representation. The methodology used in this paper is based on the acquisition of reflectivity spectra from a set of nanopowder pellets with different levels of porosity and the measurement of the transmittance spectra of KBr pellets containing low levels of silica nanoparticles. The fit of the spectra was performed with a dielectric function model through the solution of a nonlinear optimization problem including all the experimental data. In addition to the optical properties, the complete analysis also provided an accurate estimate of the total porosity of pellets and evaluated the percolation of the silica agglomerates in the porous matrix. A comparison with the predictions obtained by other mixing formulas clearly demonstrates that Bergman's theory is the most appropriate for treating this type of powder.