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Published on: February 1, 2020
Study of SF6 adsorption on graphite using infrared spectroscopy
Petros Thomas1, Yu Xia, David A Boyd
1Physics Department, University of Virginia, Charlottesville, Virginia 22904, USA.
The Journal of Chemical Physics
|October 2, 2009
Summary
This study uses infrared spectroscopy to investigate sulfur hexafluoride (SF(6)) monolayers on graphite, revealing how intermolecular spacing affects molecular vibrations and phase transitions.
Area of Science:
- Surface Science
- Condensed Matter Physics
- Infrared Spectroscopy
Background:
- Adsorbed monolayers provide a unique system to study phase transitions.
- Sulfur hexafluoride (SF(6)) is a molecule with significant dipole-dipole interactions.
Purpose of the Study:
- To experimentally investigate the behavior of SF(6) monolayers on graphite.
- To correlate spectroscopic shifts with intermolecular spacing and phase transitions.
- To determine thermodynamic properties of the SF(6) monolayer system.
Main Methods:
- Infrared reflection absorption spectroscopy (IRRAS) was employed to study SF(6) monolayers.
- Ellipsometry supplemented the spectroscopic measurements.
- Self-consistent field calculations were used to relate spectral frequency to lattice spacing.
Main Results:
- The asymmetric S-F stretch mode (nu(3)) of SF(6) showed a significant blueshift due to dynamic dipole coupling.
- The blueshift was highly sensitive to intermolecular spacing, allowing for precise lattice spacing determination (0.002 Å resolution).
- The commensurate-incommensurate transition, inter-incommensurate transitions, and melting transition were mapped.
- A new determination of the layer critical point (156 K) and condensation line was achieved.
Conclusions:
- Infrared spectroscopy is a powerful tool for probing intermolecular interactions and phase transitions in adsorbed monolayers.
- The study provides a detailed phase diagram for SF(6) on graphite, including critical parameters.
- Results offer valuable data for understanding 2D phase behavior and validating theoretical models.
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