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High Potassium Concentrations Nested in Epitaxial Monolayers of a Flexible Lander-Type Molecule on Ag(111)
journal contribution
posted on 2020-02-10, 18:09 authored by Felix Otto, Tino Kirchhuebel, Anu Baby, Falko Sojka, Guido Fratesi, Torsten Fritz, Roman ForkerThe
structural, electronic, and optical properties of organic adlayers
can be tuned to a large extent by incorporating metal atoms. Naturally,
the tunability of those properties is limited by the thermodynamic
stability of the intercalated phases obtained and the segregation
tendency, which often prevents the nesting of high metal atom concentrations
in homogeneous epitaxial compound films. Here, we employ scanning
tunneling microscopy and low-energy electron diffraction to investigate
monolayers of the polycyclic aromatic hydrocarbon tetraphenyldibenzoperiflanthene
(DBP, C64H36) epitaxially grown on Ag(111) and
intercalated with potassium. This lander-type molecule contains four
phenyl substituents that are nearly perpendicular to the aromatic
backbone, and its flexibility enables rather complex adlayer structures.
We succeeded in preparing highly ordered (mixed) monolayers with up
to six potassium atoms per DBP. For increasing K concentrations, we
find that DBP changes its shape from a considerably bent geometry
(pristine DBP and K2DBP phases) to a molecule with a planar
backbone (K6DBP phase), which is known to occur in free
DBP molecules. By means of density functional theory (DFT) calculations,
it is elucidated that the added K atoms adsorb underneath the molecule
and thereby weaken the direct bonding channels between DBP and Ag
while adding new bonding channels via the K atoms. This is accompanied
by a gradually increasing charge transfer into the lowest unoccupied
molecular orbital of DBP. The combination of structural data, results
of different spectroscopy methods, and state-of-the-art DFT calculations
leads to a comprehensive view on this rather complex host molecule–guest
atom–substrate system.
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Epitaxial Monolayerscharge transferFlexible Lander-Type Moleculemetal atomsK concentrationshydrocarbon tetraphenyldibenzoperiflanthenepotassium atomsC 64 H 36DBP changesintercalated phasesepitaxial compound filmsDBP moleculeslow-energy electron diffractionHigh Potassium Concentrations Nestedadlayer structureslander-type moleculespectroscopy methodssegregation tendencyscanning tunneling microscopyK atomsphenyl substituentsDFT calculationsK 2 DBP phasesK atoms adsorbmetal atom concentrations
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