Techniques for wide range, high resolution and precision, thermal desorption measurements. I. Principles of apparatus and operation

H. Schlichting, D. Menzel

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61 Scopus citations

Abstract

We describe techniques and an apparatus with which thermal desorption measurements, both temperature-programmed and isothermal, can be considerably improved compared to the best measurements done to date. These constitute further development of a previously used scheme (detection of desorbing species in a separate small volume which is pumped by a geometrically defined conductance to the main chamber) by procedures for very accurate resetability of the sample before the cap aperture, and by an accurate correction procedure for readsorption. Direct application of these techniques leads to a range of 4 powers of 10 in rate which can be extended by another power of 10 by a simple background correction. The dynamic range of coverages that can be studied is even larger. The very good reproducibility makes calibration of rates and coverages in absolute terms possible. The high accuracy allows studies of majority species by direct logarithmic plots, of minority species encompassing only promilles of a monolayer, and of sticking coefficients at coverages down to 10-3 and up to more than 10 monolayers, with high accuracy. While these techniques have been developed for the study of weakly adsorbed species desorbing at very low temperatures (6-100 K), they can be easily adapted to more strongly bound species, as long as the desorption products do not react with the system walls.

Original languageEnglish
Pages (from-to)209-218
Number of pages10
JournalSurface Science
Volume285
Issue number3
DOIs
StatePublished - 10 Apr 1993

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