Bis(triisopropylsilylethynyl)pentacene/Au(111)
Interface: Coupling, Molecular Orientation, and Thermal Stability
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Abstract
The
assembly and the orientation of functionalized pentacene at the interface
with inorganics strongly influence both the electric contact and the
charge transport in organic electronic devices. In this study electronic
spectroscopies and theoretical modeling are combined to investigate
the properties of the bis(triisopropylsilylethynyl)pentacene (TIPS-Pc)/Au(111)
interface as a function of the molecular coverage to compare the molecular
state in the gas phase and in the adsorbed phase and to determine
the thermal stability of TIPS-Pc in contact with gold. Our results
show that in the free molecule only the acene atoms directly bonded
to the ligands are affected by the functionalization. Adsorption on
Au(111) leads to a weak coupling which causes only modest binding
energy shifts in the TIPS-Pc and substrate core level spectra. In
the first monolayer the acene plane form an angle of 33 ± 2°
with the Au(111) surface at variance with the vertical geometry reported
for thicker solution-processed or evaporated films, whereas the presence
of configurational disorder was observed in the multilayer. The thermal
annealing of the TIPS-Pc/Au(111) interface reveals the ligand desorption
at ∼470 K, which leaves the backbone of the decomposed molecule
flat-lying on the metal surface as in the case of the unmodified pentacene.
The weak interaction with the metal substrate causes the molecular
dissociation to occur 60 K below the thermal decomposition taking
place in thick drop-cast films