Entropic stabilization of large adsorbates on weakly binding substrates-a thermal desorption and scanning tunneling microscopy study.
Thermal desorption (TD) of oligopyridine from HOPG shifts from approximately 700 to approximately 500 K when going from (sub-)mono- to multilayers. Stabilization of low coverages results from a continuous shift of the frequency factor nu, from 10(15) s(-1) for submonolayers to 10(24) s(-1) for multilayers, whereas the desorption barrier is virtually constant. Applying transition state theory (TST), we can explain this by a change from rotationally/translationally mobile, flat-lying molecules (submonolayers) to immobile, upright molecules (multilayers). At room temperature, (time resolved) scanning tunneling microscopy (STM) gives evidence for the existence and the stability of the mobile phase.
Roos
Michael
M
Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany.
Breitruck
Achim
A
Hoster
Harry E
HE
Behm
R Jürgen
RJ