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

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.

本研究所涉50纳米厚度的聚苯乙烯（PS）薄膜包含8-羟基喹啉（8HQ）分子和金纳米颗粒，该薄膜应用于某些创新性存储设备。本研究旨在验证分子局域性质与复杂系统宏观行为直接关联的模型，该模型聚焦于8HQ-PS混合物的结构和电子性质，该混合物在连续介质方案中进行建模：其中包含一个使用极化连续介质模型（PCM）模拟的8HQ分子，其可靠性已通过与8HQ-PS晶体结构的周期性DFT计算进行验证。对8HQ的酮-烯醇互变异构进行了全面研究，采用DFT水平，运用B3LYP、LC-PBE和M052X泛函以及极化双ζ基组。通过使用aug-cc-pVDZ基组在CCSD(T)水平上进行单点计算，对所得结构（极小值和过渡态）的能学进行了优化。我们的计算预测，对于孤立和PS溶剂化的中性8HQ，烯醇互变异构是最稳定的，其互变异构能垒远大于工作条件下的热能。对于带电（正负电荷）的8HQ，相反的趋势被发现，酮基互变异构是最稳定的。在弱相互作用的第一近似中，对于与铝电极的相互作用，计算8HQ分子的电子亲和力和电离势时也考虑了电场效应。这些结果得出的电子和空穴注入势垒与实验观测结果相吻合。