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Adsorption of H2O, CO2 and Xe on Soft Surfaces Ori Stein and Micha Asscher*

Summary: Adsorption of H2O, CO2 and Xe on Soft Surfaces
Ori Stein and Micha Asscher*
Department of Physical Chemistry and the Farkas Center for Light-Induced Processes,
The Hebrew UniVersity of Jerusalem, Israel
ReceiVed: October 12, 2007; In Final Form: January 10, 2008
The interactions of water, carbon dioxide, and Xe with octadecanethiol (C18H37SH, ODT) self-assembled
monolayers (SAMs) were studied under ultrahigh vacuum conditions employing temperature-programmed
desorption and optical diffraction measurements. The ODT layer was grown on a 1 nm thick gold film deposited
over a Ru(001) single-crystal substrate. The gases used in this report differ in their lateral interactions while
adsorbed on ODT-SAM being either repulsive (Xe) or attractive (H2O, CO2). The activation energies for
desorption of the first layer from ODT are Ea ) 3.6 ( 0.9, 4.1 ( 0.5, and 8.5 ( 0.9 kcal/mol for Xe, CO2,
and H2O, respectively. Sticking probabilities of the three gases on the soft ODT surface are S0 ) 0.7 ( 0.1,
0.8 ( 0.1, and 0.95 ( 0.05 for xenon, CO2, and water, respectively, derived from the respective adsorption
curves. Optical diffraction studies from multilayer coverage grating of Xe on ODT-SAM have demonstrated
that sublimation is a thermodynamically more favorable process over diffusion and wetting. The significantly
lower binding energy of the first layers of H2O and CO2 adsorbed on the soft surface of ODT compared to
that on clean metals and oxides, reflects generally weak (CO2) and hydrophobic (H2O) interactions that are
important for understanding the behavior of these molecules on interfaces that are found in biological systems.
1. Introduction
The interaction and structure of adsorbates on top of "soft"


Source: Asscher, Micha - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry