Determination of anisotropic optical constants and surface coverage of molecular films using polarized visible ATR spectroscopy. Application to adsorbed cytochrome c films

Anne F. Runge, Nicole C. Rasmussen, S. Scott Saavedra, Sergio B. Mendes

Research output: Contribution to journalArticle

20 Scopus citations

Abstract

This article describes a method to determine the anisotropic optical constants and surface coverage of molecular films using polarized attenuated total reflectance (ATR) absorbance measurements. We have extended the transfer-matrix formalism to describe birefringent and dichroic films in ATR geometries and have combined it with an iterative numerical procedure to determine the anisotropic values of both the real (n) and imaginary (k) parts of the complex refractive index of the film under investigation. Anisotropic values of the imaginary part of the refractive index (k) allow for the determination of the surface coverage and one order parameter of the film. To illustrate this approach, we have used cytochrome c (cyt c) protein films adsorbed to glass and indium tin oxide (ITO) surfaces. Experimental results show that cyt c films on these surfaces, which were formed under identical conditions, have significant differences in their surface coverages (11.2 ± 0.4 pmol/cm 2 on glass and 21.7 ± 0.9 pmol/cm 2 on ITO); however, their order parameters 〈(cos 2θ)〉 are similar (0.30 ± 0.02 on glass and 0.36 ± 0.04 on ITO).

Original languageEnglish (US)
Pages (from-to)424-431
Number of pages8
JournalJournal of Physical Chemistry B
Volume109
Issue number1
DOIs
StatePublished - Jan 13 2005

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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