A variety of two-dimensional materials have been reported in recent years, yet single-element systems such as graphene and black phosphorus have remained rare. Boron analogues have been predicted, as boron atoms possess a short covalent radius and the flexibility to adopt sp² hybridization, features that favour the formation of two-dimensional allotropes, and one example of such a borophene material has been reported recently. Here, we present a parallel experimental work showing that two-dimensional boron sheets can be grown epitaxially on a Ag(111) substrate. Two types of boron sheet, a β₁₂ sheet and a χ₃ sheet, both exhibiting a triangular lattice but with different arrangements of periodic holes, are observed by scanning tunnelling microscopy. Density functional theory simulations agree well with experiments, and indicate that both sheets are planar without obvious vertical undulations. The boron sheets are quite inert to oxidization and interact only weakly with their substrate. We envisage that such boron sheets may find applications in electronic devices in the future.

近年来，已报道了多种二维材料，但单元素体系（如石墨烯和黑磷）仍然很少见。已经预测了硼类似物，因为硼原子具有短的共价半径和采用sp ²杂交的灵活性，有利于形成二维同素异形体的特征，并且最近已经报道了这种硼苯甲酮材料的一个例子。在这里，我们提出了一个平行的实验工作，表明二维硼片可以在Ag（111）衬底上外延生长。两种类型的硼片，一个β ₁₂片和χ ₃通过扫描隧道显微镜观察到的均显示出三角形晶格但具有周期性孔的不同排列的薄板。密度泛函理论模拟与实验非常吻合，表明这两个板都是平面的，没有明显的垂直起伏。硼片对氧化反应非常惰性，并且仅能与其底物发生微弱的相互作用。我们设想这种硼片将来可能会在电子设备中找到应用。