Abstract
Since the monolayer graphene was first obtained in the year of 2004, mechanical exfoliation technique has been widely used to prepare various two-dimensional materials such as transition metal dichalcogenides and black phosphorus. Among a variety of preparation techniques of two-dimensional materials, mechanical exfoliation technique shows advantages in its simplicity and universality. More importantly, the exfoliated two-dimensional samples are the ideal ones for many novel phenomena. This paper introduces the background of mechanical exfoliation technique and summarizes the problems of conventional mechanical exfoliation technique in the development of two-dimensional materials. In order to solve the problems of low efficiency and small sample size of conventional mechanical exfoliation technique, some modified mechanical exfoliation techniques have been developed, such as oxygen-plasma-assisted exfoliation method and gold-film-assisted exfoliation method. As a commonly used “top-down” preparation method, the new exfoliation technology is still full of vitality in basic research and application of two-dimensional materials. In the future, larger size and higher quality will be the development direction of exfoliation technology.
Highlights
图 4 (a) 氧气等离子体辅助的方法制备的单层石墨烯和 Bi2212 样品 [23]; (b) 大面积的单层 Bi2212 晶体中的超导特性 [24] Fig. 4. (a) Monolayer graphene and Bi2212 samples prepared by an oxygen plasma-assisted exfoliation method[23]; (b) superconductivity in a large-area of monolayer Bi2212 crystal[24]
Sin. 70 118101 (in Chinese) [季怡汝, 褚衍邦, 冼乐德, 杨 威, 张广宇 2021 物理学报 70 118101] [23] Huang Y, Sutter E, Shi N N, Zheng J B, Yang T Z, Englund D, Gao H J, Sutter P 2015 ACS Nano 9 10612 [24] Yu Y J, Ma L G, Cai P, Zhong R D, Ye C, Shen J, Gu G D, Chen X H, Zhang Y B 2019 Nature 575 156 [25] Xu H, Meng L, Li Y, Yang T Z, Bao L H, Liu G D, Zhao L, Liu T S, Xing J, Gao H J, Zhou X J, Huang Y 2018 Acta Phys
Summary
Band structure and superconductivity in magic-angle graphene superlattices[19,20]. 通过电输运和 STM 研究, 该团队证明单 层 Bi2212 存在与块体一致的超导电性 (图 4(b)). 这种等离子体辅助的方法对于解理石墨烯和 Bi2212 效果非常明显, 但是在随后的研究中发现 该方法对于解理 TMDs 等材料效果并不显著 [25,26]. 在后续的研究中, 研究人 员发展出了利用金辅助的方法解理 TMDs 材料的 技术 [28,29], 这种新解理技术将金蒸镀在 TMDs 上, 然后结合热释放胶带将金膜转移到其他基底上, 并 通过含碘的溶液去除掉金膜. 图 4 (a) 氧气等离子体辅助的方法制备的单层石墨烯和 Bi2212 样品 [23]; (b) 大面积的单层 Bi2212 晶体中的超导特性 [24] Fig. 4. (a) Monolayer graphene and Bi2212 samples prepared by an oxygen plasma-assisted exfoliation method[23]; (b) superconductivity in a large-area of monolayer Bi2212 crystal[24]. 例 如, 针对 STM 和 ARPES 等测量设备, 可以通过 增加金属膜的厚度, 直接将二维材料解理到导电的 基底上; 而针对荧光光谱和电输运测量, 可以将金 属膜的厚度控制在 3 nm 以下, 获得绝缘性的金属 岛. 除此之外, 研究人员利用该技术在国际上首次 解理出大面积的单层 FeSe, PtSe2, PtTe2, PdTe2, CrSiTe3 等材料, 为后续开展一些新材料物性的探. 近年来金膜辅助解理技术在 一些重要的二维磁性和二维拓扑材料的研究中也 发挥了重要作用, 如 MnBi2Te4, MnSb2Te4 等材料 体系 [30,31], 都可以利用该技术获得较大尺寸的单层 和薄层单晶, 为研究其新奇量子行为提供了便利. 2020 年 2 月 21 日, 美国哥伦比亚大学研究团 队 [32] 报道了利用金辅助的方法解理大面积 TMDs 材料并堆垛出毫米量级人工晶体. 2020 年 2 月 21 日, 美国哥伦比亚大学研究团 队 [32] 报道了利用金辅助的方法解理大面积 TMDs 材料并堆垛出毫米量级人工晶体. 在这种方法中, 研究人员首先在硅片上蒸镀一层金, 再用含有水溶 性 PVP 薄膜的热释放胶带将金粘起来, 新的金表 面贴合到块体 TMDs 材料上之后再次撕下来转移 到其他基底上, 通过后续的加热和水溶解, 使得金 膜和单层 TMD 与胶带和 PVP 分离, 最后再用含 碘的溶液去掉金. 中国团队报道普适性解理技术主 要包含两步, 在任意基底上蒸镀金属膜, 然后将层 状材料贴附上之后再撕开; 美国研究团队报道的整 个制备过程包括了 9 个关键步骤, 并且涉及到液相 处理, 因此会引入一些不可控的污染, 该工作最大 的亮点在于将解理后的材料堆叠成大面积的异质 结, 这为未来探索特定转角下的异质结性质打下了 很好的基础 (见图 7)
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