Lee Jian-Jhang, Chu Yi-Hung, Yen Zhi-Long, Muthu Jeyavelan, Ting Chu-Chi, Huang Ssu-Yen, Hofmann Mario, Hsieh Ya-Ping
Department of Physics, National Taiwan University Taipei Taiwan.
Institute of Atomic and Molecular Sciences, Academia Sinica Taipei Taiwan
Nanoscale Adv. 2023 Jun 14;5(16):4074-4079. doi: 10.1039/d3na00263b. eCollection 2023 Aug 8.
Conventional exfoliation exploits the anisotropy in bonding or compositional character to delaminate 2D materials with large lateral size and atomic thickness. This approach, however, limits the choice to layered host crystals with a specific composition. Here, we demonstrate the exfoliation of a crystal along planes of ordered vacancies as a novel route toward previously unattainable 2D crystal structures. Pyrrhotite, a non-stoichiometric iron sulfide, was utilized as a prototype system due to its complex vacancy superstructure. Bulk pyrrhotite crystals were synthesized by gas-assisted bulk conversion, and their diffraction pattern revealed a 4C superstructure with 3 vacancy interfaces within the unit cell. Electrochemical intercalation and subsequent delamination yield ultrathin 2D flakes with a large lateral extent. Atomic force microscopy confirms that exfoliation occurs at all three supercell interfaces, resulting in the isolation of 2D structures with sub-unit cell thicknesses of 1/2 and 1/4 monolayers. The impact of controlling the morphology of 2D materials below the monolayer limit on 2D magnetic properties was investigated. Bulk pyrrhotite was shown to exhibit ferrimagnetic ordering that agrees with theoretical predictions and that is retained after exfoliation. A complex magnetic domain structure and an enhanced impact of vacancy planes on magnetization emphasize the potential of our synthesis approach as a powerful platform for modulating magnetic properties in future electronics and spintronics.
传统的剥离方法利用键合或成分特性中的各向异性来剥离具有大横向尺寸和原子厚度的二维材料。然而，这种方法将选择限制在具有特定成分的层状主体晶体上。在这里，我们展示了沿有序空位平面剥离晶体，这是一种通往以前无法获得的二维晶体结构的新途径。磁黄铁矿是一种非化学计量的硫化铁，由于其复杂的空位超结构，被用作原型系统。通过气相辅助体相转化合成了块状磁黄铁矿晶体，其衍射图谱揭示了一个在晶胞内具有3个空位界面的4C超结构。电化学插层和随后的剥离产生了具有大横向尺寸的超薄二维薄片。原子力显微镜证实，剥离发生在所有三个超晶胞界面处，从而分离出亚晶胞厚度为1/2和1/4单层的二维结构。研究了控制二维材料形态低于单层极限对二维磁性的影响。块状磁黄铁矿显示出亚铁磁有序，这与理论预测一致，并且在剥离后得以保留。复杂的磁畴结构以及空位平面在磁化方面的增强影响强调了我们的合成方法作为未来电子学和自旋电子学中调制磁性的强大平台的潜力。
