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Adsorption and self-assembly of large $\pi$-conjugated 3,4,9,10-perylene
tetracarboxylic dianhydride (PTCDA) molecules on rutile $TiO_{2}$(110)
surface have been investigated using a combination of high-resolution
scanning tunneling microscopy (STM), low-energy electron diffraction,
and density functional theory calculations with inclusion of Grimme
treatment of the dispersion forces (DFT-D). Evolution of the STM images
as a function of PTCDA coverage Is owed by transition of the adsorption
mode from physisorbed single adspecies and meandering stripes into
spontaneously ordered chemisorbed molecular assemblies. This change in
the adsorption fashion is accompanied by significant bending of the
intrinsically flat, yet elastic, PTCDA molecule, which allows for strong
electronic coupling of the dye adspecies with the $TiO_{2}$ substrate.
Extensive DFT-D modeling has revealed that adsorption is controlled by
interfacial and intermolecular dispersion forces playing a dominant role
in the adsorption of single PTCDA species, their self-organization into
the meandering stripes, and at the monolayer coverage acting
collectively to surmount the chemisorption energy barrier associated
with the molecule bending. Analysis of the resulting density of states
has revealed that alignment of the energy levels and strong electronic
coupling at the PTCDA/$TiO_{2}$ interface are beneficial for dye
sensitization purposes.
keywords in other languages:
supramolecular ordering, titanium dioxide, $TiO_{2}$, PTCDA, dye sensitization, photovoltaics, STM, DFT-D, van der Waals, semi-empirical dispersion, adsorption, DOS, surface functionalization
number of pulisher's sheets:
1
affiliation:
Wydział Fizyki, Astronomii i Informatyki Stosowanej : Instytut Fizyki im. Mariana Smoluchowskiego, Wydział Chemii : Zakład Chemii Nieorganicznej