2D ferroelectric material has emerged as an attractive building block for high‐density data storage nanodevices. Although monolayer van der Waals ferroelectrics have been theoretically predicted, a key experimental breakthrough for such calculations is still not realized. Here, hexagonally stacking α‐In₂Se₃ nanoflake, a rarely studied van der Waals polymorph, is reported to exhibit out‐of‐plane (OOP) and in‐plane (IP) ferroelectricity at room temperature. Ferroelectric multidomain states in a hexagonal α‐In₂Se₃ nanoflake with uniform thickness can survive to 6 nm. Most strikingly, the electric‐field‐induced polarization switching and hysteresis loop are, respectively, observed down to the bilayer and monolayer (≈1.2 nm) thicknesses, which designates it as the thinnest layered ferroelectric and verifies the corresponding theoretical calculation. In addition, two types of ferroelectric nanodevices employing the OOP and IP polarizations in 2H α‐In₂Se₃ are developed, which are applicable for nonvolatile memories and heterostructure‐based nanoelectronics/optoelectronics.

中文翻译：

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六角层状α-In2Se3纳米薄片中的室温铁电直至单层极限

二维铁电材料已成为高密度数据存储纳米器件的有吸引力的构建基块。尽管从理论上已经预测了单层范德华铁电体，但仍未实现此类计算的关键实验突破。这里，六边形层叠α-在₂硒₃纳米片，一个研究很少范德华多晶型物，据报道在室温下表现出了平面外（OOP）和面内（IP）铁电性。在六方晶的α-在强电介质多畴状态₂硒₃具有均匀厚度的纳米薄片可以存活到6 nm。最为引人注目的是，分别观察到电场致极化转换和磁滞回线直至双层和单层（≈1.2nm）厚度，这将其指定为最薄的铁电层并验证了相应的理论计算。此外，两种类型采用OOP和IP极化在铁电2H纳米器件的α-在₂硒₃被开发，这是适用于非易失性存储器和基于异质-纳米电子/光电子。