SKM 2023 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 6: New Methods: Experiments and Theory

O 6.4: Vortrag

Montag, 27. März 2023, 11:15–11:30, GER 39

Two new methods for the analysis of TPD data — •Michael Schmid, Gareth S. Parkinson, and Ulrike Diebold — Institute of Applied Physics, TU Wien, Austria

Temperature programmed desorption (TPD) is the most common experimental technique for obtaining the binding energies of adsorbates. TPD data are usually analyzed using the Polanyi--Wigner equation; this is far from straightforward. We present two new methods, based on equilibrium thermodynamics, bypassing the use of the Polanyi--Wigner equation or transition state theory: In the case of all adsorption sites being equivalent, the adsorption energy can be directly calculated from the desorption temperature, the width of the TPD peak, the sticking probability (at the desorption temperature), and thermodynamic data [1]. This ``magic formula'' is remarkably robust; in many cases even wrong assumptions about the desorption order or the presence of a distribution of adsorption energies lead to negligible errors. In more complex cases, with a distribution of adsorption energies, we show that TPD spectra are approximately given by a convolution integral. We present a method (and computer program) for TPD inversion, i.e, the determination of the energy distribution from a single TPD spectrum at saturation coverage [1]. Although this method is derived for the case of non-interacting adsorbates, we argue that it is a good approximation in cases of short-range repulsion and it can also reveal (though not quantitatively analyze) the presence of attractive interactions between adsorbates.

[1] M. Schmid et al., doi:10.1021/acsphyschemau.2c00031 (2022)