Temperature Programmed Desorption Study of Dodecanethiol Self-Assembled Monolayers on Ag

The desorption kinetics of dodecanethiol self-assembled monolayers grown on Ag films has been studied using temperature programmed desorption. The self-assembled monolayers have been grown either in solution or by vapor deposition in UHV. 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 other than methane are observed to desorb over a range of $\sim $150$^{\circ}$C to $\sim $220$^{\circ}$C. Methane desorption starts at $\sim $100 ûC and persists to $\sim $350$^{\circ}$C. In addition, the desoption of sulfur is observed starting at $\sim $220$^{\circ}$C.