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Bottom-Up Approach to Innovative Memory Devices: I. Intrinsic and Environmental Effects on the Molecular Component

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posted on 06.11.2008, 00:00 authored by Ilaria Pino, Luca Sementa, Mauro Causà, Vincenzo Barone
The 50 nm-thick polystyrene (PS) film, involved in some innovative memory devices, contains 8-hydroxyquinoline (8HQ) molecules and gold nanoparticles. A model where molecular localized properties directly reflect on macroscopic behavior of a complex system has been tested in the present work, which is focused on the structural and electronic properties of the 8HQ-PS mixture modeled in a continuum scheme: one 8HQ molecule with a polarizable continuum model (PCM) whose reliability has been checked by comparison with periodic DFT calculations of 8HQ-PS crystalline structures. A comprehensive study of the keto−enolic tautomerization of 8HQ has been performed, at the DFT level using B3LYP, LC-PBE, and M052X functionals and a polarized double-ζ basis set. The energetics of the obtained structures (minima and transition states) have been refined by single point calculations at the CCSD(T) level with the aug-cc-pVDZ basis set. Our calculations predict the enolic tautomer to be the most stable for the isolated and PS-solvated 8HQ in its neutral form, with a tautomerization barrier much larger than the thermal energy at the working conditions. The opposite trend has been found for the charged (both positive and negative) 8HQ, with ketonic tautomers being the most stable. In a first approximation of weak interaction with the aluminum electrodes, the electric-field effects have also been taken into account for the calculations of electron affinities and ionization potentials of 8HQ molecules. The electron and hole injection barriers issuing from these results are in good agreement with the experimental observations.