Ellipsometry of silica nanoparticulate Langmuir-Blodgett films for the verification of the validity of effective medium approximations

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Abstract

The validity of various effective medium approximations (EMAs) (Bruggeman, Max well-Garnett) was studied for nanostructured systems, where the scale of inhomogeneities is comparable to the wavelength. Langmuir-Blodgett (LB) layers of Stöber silica nanospheres of diameters between 40 and 129 nm are excellent model structures for the experimental verification of the validity of the EMA methods in spectroscopic ellipsometry (SE) evaluation. Nanostructured mono- and multilayered silica films were investigated by SE and reflectance spectroscopy. The effective refractive index and film thickness were determined from the results of multiparameter fitting of SE spectra in the 300-759 nm wavelength region. The distribution of the effective refractive index in the particulate films was calculated assuming an ideal close-packed arrangement of particles. The average deviation from such a structure was deduced from the corrected model by introducing a "fill factor". In the EMA approximation, the spherical shape of the silica particle determines the optical behavior, rather than the "depth distribution" of silica or porosity. Therefore, the shape of particles has a dominant effect on the optical properties of nanoparticulate LB films.

Original languageEnglish
Pages (from-to)8416-8423
Number of pages8
JournalLangmuir
Volume22
Issue number20
DOIs
Publication statusPublished - Sep 26 2006

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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