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Infrared Spectrosopy of Surfaces and Interfaces

Infrared spectroscopy is a very powerful method for the investigation of surfaces and adsorbate films with a number of distinct advatanges over other surface analytical methods:

  • It is based on a fairly cheap and straightforward instrumentation
  • It provides highly specific, molecular and structural information
  • It is sensitive to monolayer and submonolayer coverages
  • It is not restricted to a gas-phase ambient medium

Classical surface studies at solid or liquid surfaces in contact with air or vacuum can be performed as well as interface studies at solid/liquid or solid/solid phase boundaries. Our group focuses on the development and optimization of surface-sensitive techniques for the IR spectroscopic characterization of ultrathin adsorbate films on flat solid substrates. Apart from instrumental developments, this project relies heavily on computer simulations of surface infrared spectra, for which a comprehensive software package PARTS(TM) has been developed in our group. It allows not only a prediction of the optimum experimental parameters for each sampling technique, but is also an indispensable tool for the correct interpretation and quantitative evaluation of thin film IR spectra and provides access to structural details such as packing densities or surface orientation of the adsorbate molecules. Depending on the particular sample system and the optical properties of substrate and ambient phase, the following techniques are used :

1. External Reflection Infrared Spectroscopy (ERIRS, IRRAS)

Left: beam path<br>Right: IRRAS spectrum of a bilayer film of hydroxyundexanethiol (HS-(CH2)16-OH, A) and octadecyl-siloxane (OxSi-(CH)2-CH3, B) on gold