Ferroelectric Behavior in Exfoliated 2D Aurivillius Oxide Flakes of Sub-Unit Cell Thickness
Ferroelectric Behavior in Exfoliated 2D Aurivillius Oxide Flakes of Sub-Unit Cell Thickness
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DOI：
10.1002/aelm.201901264
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发表时间：
2020-01-30
影响因子：
6.2
通讯作者：
Whatmore, Roger W.
中科院分区：
文献类型：
--
作者：
Keeney, Lynette;Smith, Ronan J.;Whatmore, Roger W.
研究了不同厚度的层状氧化金Bi5Ti3Fe0.5Co0.5O15在超声作用下剥离后的铁电性。这些薄片具有相对较大的面积(线性尺寸是薄膜厚度的许多倍)，因此将它们归类为2D材料。结果表明，铁电性可以存在于厚度仅为2.4 nm的片状晶体中，相当于正常晶胞的一半。压电响应力显微镜(PFM)表明，这些非常薄的薄片既表现出压电效应，又可以可逆地切换铁电极化。提出了一种新的模型，该模型可以准确地模拟在电极-氧化物界面存在电荷注入、存储和衰减的情况下，铁电开关过程中的场开场和场关场PFM的时间域和磁滞回线响应。提取的自发极化系数为0.04(+/-0.02)Cm(-2)，电致伸缩系数为2(+/-0.1)×10(-2)m(4)C-2，与其它铁电Aurivillius氧化物的结果一致。矫顽场随厚度变化，严格遵循铁电材料的半经验标度律。这构成了2D氧化物材料中铁电性的第一个证据，并提供了可能利用与2D材料形式的可切换铁电自发极化相关的有用性质的新器件的前景。
Ferroelectricity in ultrasonically exfoliated flakes of the layered Aurivillius oxide Bi5Ti3Fe0.5Co0.5O15 with a range of thicknesses is studied. These flakes have relatively large areas (linear dimensions many times the film thickness), thus classifying them as 2D materials. It is shown that ferroelectricity can exist in flakes with thicknesses of only 2.4 nm, which equals one-half of the normal crystal unit cell. Piezoresponse force microscopy (PFM) demonstrates that these very thin flakes exhibit both piezoelectric effects and that the ferroelectric polarization can be reversibly switched. A new model is presented that permits the accurate modeling of the field-on and field-off PFM time domain and hysteresis loop responses from a ferroelectric during switching in the presence of charge injection, storage, and decay through a Schottky barrier at the electrode-oxide interface. The extracted values of spontaneous polarization, 0.04(+/- 0.02) C m(-2) and electrostrictive coefficient, 2(+/- 0.1) x 10(-2) m(4) C-2 are in good agreement with other ferroelectric Aurivillius oxides. Coercive field scales with thickness, closely following the semi-empirical scaling law expected for ferroelectric materials. This constitutes the first evidence for ferroelectricity in a 2D oxide material, and it offers the prospect of new devices that might use the useful properties associated with the switchable ferroelectric spontaneous polarization in a 2D materials format.