独立单原子厚二维(2D)金属膜:一类新型的二维材料

从石墨中分离出单原子厚的石墨烯层具有重要的科学意义，石墨烯引发了人们对其他(独立的)范德华层状材料的极大兴趣，如六方氮化硼(hBN)和过渡金属双卤代烷(TMDs)。无分层晶体结构的材料的原子薄层也可以以二维结构存在。如，硅可以生成硅烯，锡可以生成锡烯，锗可以生成锗烯。然而，这些都被证明存在于衬底上，是否可作为独立结构存在(即无衬底)还未得到证实。近年来，利用密度泛函理论系统的研究表明，二维元素金属族由45种元素组成，许多金属可以作为单原子厚结构独立存在。因此，理论和早期实验数据表明，存在一类新的二维金属材料，可作为单原子厚的晶体层独立且稳定存在，等待被发现。本课题的主要目标是利用原子分辨率原位透射电子显微镜对新型二维金属材料进行系统的实验和理论研究。元素周期表中118种元素中有91种是金属，因此，为证明这种新型单原子厚二维金属独立且稳定存在而提出的系统研究有望在科学和社会领域产生重大影响。

The isolation of a single-atom-thick layer of graphene from graphite was significant for numerous scientific reasons, including, proof that a.single-atom-thick layer could be physically stable, even as a freestanding structure. Graphene launched great interest in other (freestanding) van der Waals layered materials such as hexagonal boron nitride (hBN) and the transition metal dichalcogenides (TMDs). Atom thin bulk materials which do not adopt a layered structure can also exist as a 2D structure. For example, silicon can yield a mono-atomic layer as silicene, tin can yield stanine and germanium can yield germanene. However, these have all been shown to exist on a substrate but it is.unclear if they can exist as freestanding structures (i.e. no substrate interaction). A true single-atom-thick 2D layered material should be sufficiently stable to exist as a freestanding structure such as graphene, hBN and TMDs can. Experimental confirms the existence of freestanding single-atom-thick metal membranes and shows promise. Compared to covalent 2D materials, metallic bonding prefers close-packed structures rather than layered ones. For this reason, freestanding single atom materials with metallic bonding are elusive. Theoretical studies suggest that many metals can exist as single-atom-thick freestanding layers. In particular, recently, a systematic study using.density-functional theory showed a family of elemental 2D metals consisting of 45 elemental metals. Hence, theory and early experimental data suggest there is a new class of 2D elemental metals that can exist as freestanding single-atom-thick crystalline layers waiting to be discovered. The primary goal of this project is to conduct systematic studies with atom resolution in situ transmission electron microscopy to fabricate and characterize new freestanding single-atom-thick 2D metals together with supporting theory. With 91 of the 118 elements in the periodic table being metals, the proposed systematic seed project to prove the existence of this new class of freestanding single-atom-thick 2D metals can be.expected to have significant impact within science and society.