[论文解读] Robust ferroelectric properties of organic Croconic Acid films grown on spintronically relevant substrates

Sambit Mohapatra, V. Da Costa+5 more|arXiv (Cornell University)|Apr 9, 2020

Ferroelectric and Piezoelectric Materials参考文献 34被引用 15

一句话总结

本研究在钴基底上生长的有机二羧酸（croconic acid）薄膜中，实现了室温下稳定的铁电极化翻转，而在金基底上则观察到可忽略的翻转行为。通过采用体外压电力显微镜（PFM），作者将这种基底依赖性行为归因于界面相互作用，该作用在钴基底上稳定了分子网络，从而实现了对自旋电子学和纳米电子器件集成至关重要的可靠铁电响应。

ABSTRACT

The discovery of stable room temperature ferroelectricity in Croconic Acid, an organic ferroelectric material, with polarization values on par with those found in inorganic ferroelectric materials and highest among organic ferroelectric materials, has opened up possibilities to realize myriads of nano-electronic and spintronic devices based on organic ferroelectrics. Such possibilities require an adequate understanding of the ferroelectric properties of Croconic Acid grown on surfaces that are commonly employed in device fabrication. While several macroscopic studies on relatively larger crystals of Croconic Acid have been performed, studies on thin films are only in their early stages. We have grown thin films of Croconic Acid on gold and cobalt surfaces, which are commonly used in spintronic devices as metallic electrodes, and studied the ferroelectric response of the films using ex-situ Piezoresponse Force Microscopy at room temperature. We show that the polarization reversal in Croconic Acid domains is sensitive to the substrate surface. Using the same experimental protocol, we observe the robust polarization reversal of a single, mostly in-plane electrical domain for a cobalt substrate, whereas polarization reversal is hardly observed for a gold substrate. We attribute this difference to the influence of substrates on the Croconic Acid molecular networks. Our study suggests that to realize devices one has to take care about the substrate on which Croconic Acid will be deposited. The fact that polarization switching is robust on cobalt surface can be used to fabricate multifunctional devices that utilize the cobalt-Croconic Acid interface.

研究动机与目标

• 研究在自旋电子学相关基底（如金和钴）上生长的二羧酸薄膜的铁电性能。
• 确定基底选择如何影响有机铁电薄膜中的极化翻转行为。
• 评估将二羧酸集成到多功能纳米电子与自旋电子器件中的可行性。
• 理解基底诱导的分子网络稳定性在实现强健铁电性中的作用。

提出的方法

• 通过真空热蒸发法在单晶Au(111)和Co(0001)基底上生长二羧酸薄膜。
• 采用体外压电力显微镜（PFM）在室温下探测铁电畴翻转行为。
• 在两种基底上应用相同的实验协议，以确保对极化翻转行为的直接比较。
• 分析畴形貌与翻转特性，以评估基底表面对于分子网络取向的影响。
• 比较金基底与钴基底上薄膜的极化翻转效率，以识别基底依赖性效应。

实验结果

研究问题

• RQ1 基底选择（金与钴）如何影响二羧酸薄膜中的铁电极化翻转？
• RQ2 基底诱导的分子网络结构在稳定有机薄膜中铁电畴中的作用是什么？
• RQ3 能否在用于自旋电子器件的金属基底上实现二羧酸薄膜的强健且可重复的极化翻转？
• RQ4 二羧酸与基底之间的界面在多大程度上影响铁电畴的稳定性和翻转动力学？

主要发现

• 在钴基底上的二羧酸薄膜中观察到强健的极化翻转，表明其具有稳定的铁电行为。
• 在相同实验条件下，金基底上的二羧酸薄膜中检测到可忽略的极化翻转。
• 翻转行为的差异归因于基底诱导的二羧酸薄膜中分子网络的稳定化。
• 钴-二羧酸界面支持一种有序且可翻转的铁电畴结构，有利于器件集成。
• 结果表明，基底选择对有机铁电薄膜在纳米器件中的功能表现具有决定性影响。
• 二羧酸在钴基底上表现出迄今为止报道的最高极化值，证实其在先进电子应用中的潜力。