Dopamine on TiO2 anatase surfaces
Ines Urdaneta
ISMO, Orsay, France et FAMA-UAM, Mexico, Mexique
Mardi 27 Novembre 2012, 14h00
bibliothèque LCT, tour 12 - 13, 4e étage
Very recently considerably attention has been given to the adsorption of organic molecules on TiO2 clusters, since these systems have shown an important increase of the emitted Raman signal with respect to the bare molecule, effect known as surface enhanced Raman signal (SERS). Recent experiments have shown that the hybrid system TiO2-dopamine presents this SERS effect which was first observed on molecules on rough metallic surfaces, while theoretical studies with small TiO2 clusters have concluded that the role of the dopamine's attachment to the surface is two-fold; (i) it gives rise to new occupied states (coming mainly from the molecule) inside the cluster's original band gap, and (ii) it gives rise to a large polarizability difference between the HOMO-LUMO orbitals of the complex since the HOMO is localized mainly in the molecule while the LUMO is mostly placed in the nanocluster. This last indicates a charge transfer (CT) mechanism from the molecule to the nanoparticle which could be responsible in principle for the increase in the Raman signal.
Nevertheless, up to now little is known about the behavior of dopamine on TiO2 surfaces. In order to explore this area, I have performed three studies for the system concerning the adsorption of Dopamine molecule on three anatase surfaces (001), (100), (101) using VASP. The most stable structure among different plausible configurations is presented. The second study is held for multiple molecule coverage, while a third study is done to see the impact of water molecules on the dopamine adsorption on each surface. As we will see further on, the surface orientation is water or molecule selective, i.e, depending on the surface exposed, dopamine molecules may or may not adsorb to it in the presence of water.
For each surface orientation, the most stable structure is evaluated in terms of electronic structure and DOS in its singlet and triplet state in order to mimic an excitation. This will provide an insight of the dependence of the charge localization giving rise to a charge transfer (CT) with respect to hydration degree and surface orientation.