posted on 2024-01-10, 22:12authored byRobert Bavisotto, Wilfred T. Tysoe
This paper describes a method by
which surface-reaction kinetics
can be measured by slowly and precisely ramping up the surface temperature
at a constant rate while simultaneously collecting X-ray photoelectron
spectra (XPS). This approach results in the collection of a large
amount of data over relatively small temperature steps to produce
quasi-continuous kinetic data. The method is illustrated for the desorption
and reaction of diethyl disulfide (DEDS) on a Au(111) substrate in
ultrahigh vacuum, where the results can be compared with previous
conventional temperature-programmed desorption (TPD) data from Au(111).
Experiments were carried out using a double-pass cylindrical-mirror
analyzer with a channeltron detector to demonstrate how this approach
can be implemented in a routine, multitechnique vacuum chamber. The
approach will be even more effective in a more modern, specialized
XPS apparatus with high-transmission hemispherical analyzers with
multichannel array detectors, which will enable the spectra of several
elements to be measured simultaneously. The results yielded an activation
energy for multilayer desorption of DEDS of 41 ± 1 kJ/mol, with
a pre-exponential factor of 8 ± 7 × 1012 s–1, an activation energy of 53 ± 6 kJ/mol and pre-exponential
factor of 9 ± 8 × 1013 s–1 for
monolayer desorption and an activation energy of 90 ± 6 kJ/mol
with a prefactor of 1.0 ± 0.3 × 1015 s–1 for the reaction of adsorbed ethyl thiolate species to adsorbed
DEDS. While these results were collected for a system for which the
kinetic data could have been obtained using conventional TPD, this
method can be more usefully applied to those surface reaction processes
that do not rely on the formation of desorption products. This system,
having been previously studied by TPD, facilitates a comparison with
results obtained by conventional methods.