Reflectometric spectroscopy of adsorbed molecular layers

Area of Science:

• Surface science
• Spectroscopy
• Thin-film analysis

Background:

• Characterizing molecular layers on surfaces is crucial for understanding adsorption phenomena.
• Infrared (IR) spectroscopy is a powerful tool for molecular identification and analysis.
• Existing techniques may have limitations in sensitivity or applicability to thin films.

Purpose of the Study:

• To develop and describe a novel normal-incidence technique for obtaining IR absorption spectra.
• To investigate molecular layers adsorbed on a dielectric thin-film surface.
• To compare the spectral features of adsorbed layers with the bulk liquid spectrum.

Main Methods:

• Utilized a normal-incidence experimental setup.
• Employed a low-power carbon dioxide (CO2) laser beam.
• Scanned the laser across molecular layers of 2-propanol adsorbed on a zinc selenide (ZnSe) film.
• Obtained IR absorption spectra at various monolayer coverages (1-5 ML).

Main Results:

• Successfully obtained IR absorption spectra of 2-propanol molecular layers.
• Demonstrated the capability of the technique for analyzing thin adsorbed films.
• Compared spectra from 1-5 monolayer coverages with the liquid spectrum of 2-propanol.

Conclusions:

• The described normal-incidence technique is effective for characterizing molecular layers on dielectric surfaces.
• The method provides valuable insights into the spectral changes upon adsorption.
• This technique offers a new approach for studying surface-adsorbate interactions using IR spectroscopy.