Temperature Programmed Desorption Study of Dodecanethiol Self-Assembled Monolayers on Ag
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The desorption kinetics of dodecanethiol self-assembled monolayers grown on Ag films has been studied using temperature programmed desorption. The Ag films were grown on Si(100) substrates by physical vapor deposition in a high vacuum system. The self-assembled monolayers have been grown either in solution or by vapor deposition in ultra high vacuum. The direct detection of dodecanethiol by the residual gas analyzer gives a complex spectrum due to multiple cracking fragments that are produced during the ionization of the molecule. The temperature programmed desorption measurements indicate that desorption of the self-assembled monolayer occurs in a two-stage process: dissociation of the alkane chain followed by desorption of the sulfur from the surface. Alkane chain fragments are observed to desorb over a range of about 100°C to about 220°C, and the desorption of sulfur is observed starting around 200°C. Analysis of the relative coverage of the self-assembled monolayers was performed by measuring the areas under the pressure versus time curves. These results show that the saturation coverage is similar for both the vapor deposited and the solution grown self-assembled monolayers.