Raman spectroscopic characterization of a thiophene-based active material for resistive organic nonvolatile memories
作者:Daniele Fazzi、Eleonora Valeria Canesi、Chiara Bertarelli、Chiara Castiglioni、Fabrizia Negri、Giuseppe Zerbi
DOI:10.1002/jrs.2449
日期:2010.4
A combined theoretical and experimental Raman study is presented on a diphenyl bithiophene molecule known as a good candidate for the development of organic nonvolatile memory devices. Spectroscopic markers suitable to distinguish the different stable conformers of the molecule have been predicted and detected. The combined analysis of theoretical and experimental Raman spectra recorded in solution indicates that at room temperature a dynamical equilibrium, characterized by interconversion between the two more stable conformers (namely trans and cis), takes place and that the more populated species is the cis form. Referring to the solid phase instead, Raman spectra of single-crystal samples show the presence of the only trans conformer, as confirmed by X-ray measurements. Finally, Raman spectra of thin films, as those used for the memory device, were collected; samples just deposited from solution and after few hours from the deposition were analyzed. Following the evolution of selective spectroscopic Raman markers, an isomerization process from the abundant cis (as-deposited) to the totally trans (after few hours) conformer in the solid phase was detected. These results open the way to the identification of the molecular isomers present in the thin film of the memory cell and finally of the active molecular species involved in the switching mechanism of the operating device. Copyright © 2009 John Wiley & Sons, Ltd.
本文对二苯基双噻吩分子进行了理论分析和实验拉曼研究,该分子被认为是开发有机非挥发性存储器的理想候选材料。本文预测并检测了可用于区分分子不同稳定构象的光谱标记。对溶液中记录的理论拉曼光谱和实验拉曼光谱进行综合分析表明,在室温下,两种更稳定的构象(即反式和顺式)之间会发生相互转化,形成动态平衡,其中顺式构象的数量更多。而固体相的单晶样品拉曼光谱则显示只有反式构象存在,这一点得到了X射线测量的证实。最后,本文收集了用于存储器的薄膜拉曼光谱,并对刚从溶液中沉积的样品以及沉积几小时后样品进行了分析。根据选择性光谱拉曼标记的变化,本文检测到了从大量顺式构象(刚沉积)到完全反式构象(几小时后)的固体相异构化过程。这些结果为识别存储单元薄膜中的分子异构体以及操作器件切换机制中涉及的活性分子种类开辟了道路。版权所有 © 2009 John Wiley & Sons, Ltd.