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Updated: Jul 5, 2026

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone (ITZ)

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Published on: December 16, 2019

Large entropy difference between terrace and step sites on surfaces.

David E Starr¹, Charles T Campbell

¹Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA.

Journal of the American Chemical Society

|May 16, 2008

Summary

We found a significant entropy difference between lead (Pb) atoms on terrace and step sites on molybdenum (Mo)(100) surfaces. This difference impacts defect site population and is key for understanding surface adsorption at high temperatures.

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Area of Science:

Surface Science
Physical Chemistry
Materials Science

Background:

Understanding adsorbate behavior on surfaces is crucial for catalysis and materials science.
Desorption kinetics, including prefactors and activation energies, provide insights into adsorbate-surface interactions.
Distinguishing between terrace and step site properties is essential for detailed surface analysis.

Purpose of the Study:

To investigate the desorption kinetics of low-coverage lead (Pb) from a molybdenum (Mo)(100) surface.
To determine the thermodynamic properties, specifically entropy differences, between Pb atoms at terrace and step sites.
To model the behavior of adsorbates on surfaces at high temperatures.

Main Methods:

Atomic beam/surface scattering measurements were employed to study desorption kinetics.
Line shape analysis of transient desorption signals identified species with different surface lifetimes.
Arrhenius analysis of lifetimes at high temperatures (1150–1320 K) determined desorption prefactors and activation energies.

Main Results:

Two distinct Pb species with different desorption lifetimes were observed on the Mo(100) surface.
Desorption activation energies of 332 kJ/mol (terrace) and 411 kJ/mol (step) were determined.
A large entropy difference (82 J/(mol K)) was found between terrace (2D ideal gas) and step (1D ideal gas) sites.

Conclusions:

The study reveals a significant entropy-driven preference for terrace sites over step sites at high temperatures.
This entropy difference explains why defect sites are less populated than predicted by enthalpy alone.
The findings are generalizable to other adsorbate/surface systems where thermal energy exceeds diffusion barriers.