Two-dimensional (2D) boron (that is, borophene) was recently synthesized following theoretical predictions^1,2,3,4,5. Its metallic nature and high in-plane anisotropy combine many of the desirable attributes of graphene⁶ and monolayer black phosphorus⁷. As a synthetic 2D material, its structural properties cannot be deduced from bulk boron, which implies that the intrinsic defects of borophene remain unexplored. Here we investigate borophene line defects at the atomic scale with ultrahigh vacuum (UHV) scanning tunnelling microscopy/spectroscopy (STM/STS) and density functional theory (DFT). Under suitable growth conditions, borophene phases that correspond to the v_1/6 and v_1/5 models are found to intermix and accommodate line defects in each other with structures that match the constituent units of the other phase. These line defects energetically favour spatially periodic self-assembly that gives rise to new borophene phases, which ultimately blurs the distinction between borophene crystals and defects. This phenomenon is unique to borophene as a result of its high in-plane anisotropy and energetically and structurally similar polymorphs. Low-temperature measurements further reveal subtle electronic features that are consistent with a charge density wave (CDW), which are modulated by line defects. This atomic-level understanding is likely to inform ongoing efforts to devise and realize applications based on borophene.

二维（2D）硼（即硼苯）是根据理论预测^1,2,3,4,5最近合成的。它的金属性质和高的面内各向异性将石墨烯⁶和单层黑磷^7的许多理想属性结合在一起。作为合成的2D材料，其结构性质无法从块状硼中推论得出，这意味着尚未发现硼苯的内在缺陷。在这里，我们使用超高真空（UHV）扫描隧道显微镜/光谱学（STM / STS）和密度泛函理论（DFT）在原子尺度上研究了硼烯线缺陷。在合适的生长条件下，硼烷相对应于v _1/6和v _1/5发现模型可以相互混合并以与另一相的组成单元匹配的结构相互适应线缺陷。这些线缺陷在能量上有利于空间周期性的自组装，从而产生新的硼芬相，这最终模糊了硼芬晶体与缺陷之间的区别。由于其高的平面各向异性以及在能量和结构上相似的多晶型物，这种现象是硼芬所独有的。低温测量进一步揭示了与电荷密度波（CDW）一致的细微电子特征，电荷密度波由线路缺陷调制。这种原子级的理解可能会为正在进行的基于borophene的应用程序的设计和实现做出努力。