Abstract
The adsorption structure of truxenone on Cu(111) was determined quantitatively using normal-incidence X-ray standing waves. The truxenone molecule was found to chemisorb on the surface, with all adsorption heights of the dominant species on the surface less than ∼2.5 Å. The phenyl backbone of the molecule adsorbs mostly parallel to the underlying surface, with an adsorption height of 2.32 ± 0.08 Å. The C atoms bound to the carbonyl groups are located closer to the surface at 2.15 ± 0.10 Å, a similar adsorption height to that of the chemisorbed O species; however, these O species were found to adsorb at two different adsorption heights, 1.96 ± 0.08 and 2.15 ± 0.06 Å, at a ratio of 1:2, suggesting that on average, one O atom per adsorbed truxenone molecule interacts more strongly with the surface. The adsorption geometry determined herein is an important benchmark for future theoretical calculations concerning both the interaction with solid surfaces and the electronic properties of a molecule with electron-accepting properties for applications in organic electronic devices.
Highlights
Monolayers and sub-monolayers of electronically conjugated organic molecules are the compulsory first steps in building films and crystals for devices and applications
We present synchrotron X-ray photoelectron spectroscopy (XPS) and a quantitative normal-incidence X-ray standing wave (NIXSW)[15] measurement of the chemical and geometric structure of truxenone deposited on the Cu(111) surface
Three different O species were observed in XPS spectra at a binding energy of 530.1, 530.8, and 532.5 eV
Summary
Monolayers and sub-monolayers of electronically conjugated organic molecules are the compulsory first steps in building films and crystals for devices and applications. At these early stages of growth, a wide variety of structural polymorphs and bonding motifs can be observed even when only a single type of molecule is present. Changes in the bonding motif can affect how well molecules interact electronically with substrates[1] and their thermal stability[2] and can even modify their electronic properties.[3] For these reasons, determining the structure at this stage of growth is of the utmost importance to understand how and why molecular semiconductors assemble.
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