Ellipsometric characterisation of heterogeneous 2D layers

Herbert Wormeester, E. Stefan Kooij, Agnes Mewe, Sander Rekveld, Bene Poelsema

Research output: Contribution to journalArticleAcademicpeer-review

25 Citations (Scopus)

Abstract

Heterogeneous two-dimensional layers have been the subjects of many ellipsometric studies. An unambiguous characterization of especially metal heterogeneous layers is not straightforward. Adsorption of Au nanocolloids leads to a well-defined heterogeneous layer, although the analysis of ellipsometric spectra is not simple. Standard effective medium theories are shown not to be capable of a correct description. The thin island film theory developed by Bedeaux and Vlieger (Optical properties of surface Imperial College Press (2002)), which evaluates a spherical Au colloid as an excess polarizability at the surface, provides a good framework for the analysis. Both the image dipole and the lateral distribution can be incorporated in a straightforward manner. The influence of the change in particle shape from spherical to prolate is evaluated and shows that already a small change in shape leads to large influences in the optical response. This strong effect is due to the influence of shape on the depolarization factors and especially due to the large optical contrast between the Au colloids and the ambient. In contrast to this, the adsorption of the strongly aspherical protein fibrinogen can be analyzed straightforwardly. Only the adsorbed amount of protein on the surface is recorded in-situ. This is the result of the minimal refractive index contrast between proteins and water, which results in a negligible influence of shape on the optical response.
Original languageEnglish
Pages (from-to)323-334
Number of pages12
JournalThin solid films
Volume455
Issue number56
DOIs
Publication statusPublished - 2004
Event3rd International Conference on Spectroscopic Ellipsometry, ICSE 2003 - Vienna, Austria
Duration: 6 Jul 200311 Jul 2003
Conference number: 3

Keywords

  • Au colloids
  • Heterogeneous two-dimensional layers
  • Ellipsometric characterisation
  • METIS-220913
  • IR-75166

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