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石墨(烯)上的Na2Cl和CaCl二维晶体

Two-dimensional Na2Cl and CaCl crystals on graphitic surfaces

  • 摘要: 众所周知,钠原子有一个价电子,钙原子有两个价电子,所以它们的晶体结构是NaCl和CaCl2及类似形式,没有磁性且呈现绝缘性。文章回顾了近期在石墨烯膜上观察到的自然环境下生成的阴阳离子比例反常(反常化学计量比)的Na2Cl和CaCl二维晶体。由于阴阳离子比例反常,CaCl二维晶体具有异常电子性质,不再是绝缘体、抗磁物质,而是具有室温铁磁性、金属性、金属行为和压电行为共存等反常的物理性质;Na2Cl二维晶体因包含周期性的单原子空位(由于Na和Cl原子比例是2∶1,导致应该有Cl原子的位置是空的),则会有更特殊的行为,例如极高灵敏度的压电响应。基于同步辐射的研究还表明,Ca离子的光谱显示出它既不是二价离子,也不是零价金属,而是一种特殊的离子状态。这些具有反常化学计量比的材料,有望拓展新颖电子器件的系统研发和应用。如果能将其应用扩展到生物体系,则可以为理解生物磁性提供新的思路。

     

    Abstract: It is well-known that the valence states of sodium and calcium ions under ambient conditions are +1 and +2, respectively, and the corresponding crystals with these ions are insulating and cannot be ferromagnetic. In this paper, we review the recent discovery of two-dimensional Na2Cl and CaCl crystals on reduced graphene oxide membranes under ambient conditions. Due to the abnormal ratio of the cations and anions in the crystal (unconventional stoichiometries), the two-dimensional CaCl crystals display metallicity, room-temperature ferromagnetism, and coexistence of piezoelectricity and metallicity under ambient conditions. Soft X-ray absorption spectroscopy performed with synchrotron radiation shows that the Ca ions are not divalent, indicating that they are in a new state. These crystals with unconventional stoichiometries have practical potential applications in designing novel transistors and magnetic devices with sizes down to the atomic scale. If we could apply these findings to biological systems, we may obtain new insights into the understanding of biomagnetism, including the origin of magnetoreception and magnetogenetics.

     

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