Solids, Vol. 6, Pages 38: From Na2Cl to CaCl: Progress in the 2D Crystals of Unconventional Stoichiometries in Ambient Conditions

Solids doi: 10.3390/solids6030038

Authors:
Mengjiao Wu
Xiaoling Lei
Haiping Fang

Two-dimensional (2D) crystals which present unconventional stoichiometries on graphene surfaces in ambient conditions, such as Na2Cl, Na3Cl, and CaCl, have attracted significant attention in recent years due to their electronic structures and abnormal cation–anion ratios, which differ from those of conventional three-dimensional crystals. This unconventional crystallization is attributed to the cation–π interaction between ions and the π-conjugated system of the graphene surface. Consequently, their physical and chemical properties—including their electrical, optical, magnetic, and mechanical characteristics—often differ markedly from those of conventional crystals. This review summarizes the recent progress made in the fabrication and analysis of the structures, distinctive features, and applications of these 2D unconventional stoichiometry crystals on graphene surfaces in ambient conditions. Their special properties, including their piezoelectricity, metallicity, heterojunction, and room-temperature ferromagnetism, are given particularly close attention. Finally, some significant prospects and further developments in this exciting interdisciplinary field are proposed.

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Mengjiao Wu www.mdpi.com