Four-parameter model of thin surface layer contribution to reflectance-absorbance spectroscopy and ellipsometry

Area of Science:

• Surface science
• Optical physics
• Materials science

Background:

• Reflection coefficients are influenced by surface layer properties.
• Quantifying surface contributions requires understanding complex permittivity excesses.
• Existing angular reflection-absorption spectroscopy is insufficient to determine all surface parameters.

Purpose of the Study:

• To develop a method for determining the four surface integral values that define the surface layer's contribution to reflection coefficients.
• To establish the relationship between reflectance-absorbance spectra and surface integral spectra.
• To validate the theoretical analysis with experimental data.

Main Methods:

• Theoretical analysis relating surface integral values to complex permittivity excesses.
• Inclusion of spectroscopic ellipsometry or polarization-modulation infrared reflection absorption spectroscopy data.
• Measurement of angular dependence of absorbance for p-polarized radiation reflected from a DPPC monolayer on water.

Main Results:

• Four surface integral values, interpretable as complex permittivity excesses, determine surface layer contributions.
• Reflectance-absorbance spectra are governed by the spectra of these surface parameters.
• Experimental absorbance measurements for a DPPC monolayer showed good agreement with the theoretical model.

Conclusions:

• Determining surface excess integrals requires advanced spectroscopic techniques beyond standard reflection-absorption measurements.
• The proposed theoretical framework accurately models surface contributions to optical properties.
• Experimental validation confirms the utility of the developed method for characterizing surface layers.