CuInP2S6 Room Temperature Layered Ferroelectric
CuInP2S6 Room Temperature Layered Ferroelectric
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DOI：
10.1021/acs.nanolett.5b00491
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发表时间：
2015-06-01
期刊：
影响因子：
10.8
通讯作者：
Kalinin, S. V.
中科院分区：
文献类型：
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作者：
Belianinov, A.;He, Q.;Kalinin, S. V.
我们探讨的铁电性质的切割2-D薄片的铜铟硫代磷酸盐，CuInP 2S 6（CITP），和探针尺寸效应沿着与铁电相稳定性的限制，通过环境和超高真空扫描探针显微镜。CITP属于已知在室温及以上的货车德瓦尔斯层状晶体中显示铁电极化的唯一材料家族。我们的测量直接揭示了稳定的铁电极化，证明了域结构，可切换的极化，和磁滞回线。我们发现，在室温下的域结构的薄片厚于100 nm的是类似的解理体表面，而低于50 nm的极化消失。我们将这种行为归因于一个众所周知的不稳定性的偏振由于退极化场。此外，在高偏压下的极化切换也与离子迁移率相关，如通过宏观测量和在4 V的偏压下可能由于铜还原而在尖端下形成的表面损伤所证明的。因此，移动的Cu离子也可能有助于内部屏蔽机制。范德瓦尔斯晶体中稳定极化的存在自然指向极性材料、准2D和单层材料的最终缩放的新策略，这些材料具有先进的非线性介电特性，目前在不断增长的“石墨烯家族”的任何成员中都没有发现。
We explore ferroelectric properties of cleaved 2-D flakes of copper indium thiophosphate, CuInP2S6 (CITP), and probe size effects along with limits of ferroelectric phase stability, by ambient and ultra high vacuum scanning probe microscopy. CITP belongs to the only material family known to display ferroelectric polarization in a van der Waals, layered crystal at room temperature and above. Our measurements directly reveal stable, ferroelectric polarization as evidenced by domain structures, switchable polarization, and hysteresis loops. We found that at room temperature the domain structure of flakes thicker than 100 nm is similar to the cleaved bulk surfaces, whereas below 50 nm polarization disappears. We ascribe this behavior to a well-known instability of polarization due to depolarization field. Furthermore, polarization switching at high bias is also associated with ionic mobility, as evidenced both by macroscopic measurements and by formation of surface damage under the tip at a bias of 4 V-likely due to copper reduction. Mobile Cu ions may therefore also contribute to internal screening mechanisms. The existence of stable polarization in a van-der-Waals crystal naturally points toward new strategies for ultimate scaling of polar materials, quasi-2D, and single-layer materials with advanced and nonlinear dielectric properties that are presently not found in any members of the growing "graphene family".