Structured Layer of Rhenium Dye on SiO<sub>2</sub> and TiO<sub>2</sub> Surfaces by Langmuir–Blodgett Technique
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Abstract
We
demonstrate the Langmuir–Blodgett assembly of two rhenium–bipyridine
complexes containing a flexible or an aromatic bridge, and transfer
of the monolayer to SiO<sub>2</sub> and single crystal TiO<sub>2</sub> substrates. Both of the complexes (ReEC and Re2TC) have a hydrophilic
carboxylic acid group, which preferentially anchors into the water
subphase, and forms stable monolayers at surface pressures up to 40
mN/m. The optimum conditions for the formation of complete monolayers
of both ReEC and Re2TC were identified through characterization of
the morphology by atomic force microscopy (AFM), the thickness by
ellipsometry, and the surface coverage by X-ray photoelectron spectroscopy
(XPS). X-ray reflectivity measurements (XRR) are consistent with the
orientation of the molecules normal to the substrate, and their extension
to close to their calculated maximum length. Parameters derived from
XRR analysis show that there is a higher packing density for Re2TC
monolayers than for ReEC monolayers, attributable to the more rigid
bridge in the Re2TC molecule