Interhalogen compounds (IHCs) are extremely reactive molecules used for halogenation, catalyst, selective etchant, and surface modification. Most of the IHCs are unstable at room temperature especially for the iodine-monofluoride (IF) whose structure is still unknown. Here we demonstrate an unambiguous observation of two-dimensional (2D) IF bilayer grown on the surface of WSe₂ by using scanning transmission electron microscopy and electron energy loss spectroscopy. The bilayer IF shows a clear hexagonal lattice and robust epitaxial relationship with the WSe₂ substrate. Despite the IF is known to sublimate at −14 °C and has never found as a solid form in the ambient condition, but surprisingly it is found stabilized on a suitable substrate and the stabilized structure is supported by a density functional theory. This 2D form of IHC is actually a byproduct during a chemical vapor deposition growth of WSe₂ in the presence of alkali metal halides as a growth promoter and requires immediate surface passivation to sustain. This work points out a great possibility to produce 2D structures that are unexpected to be crystallized or cannot be obtained by a simple exfoliation but can be grown only on a certain substrate.

卤间化合物（IHC）是用于卤化，催化剂，选择性蚀刻剂和表面改性的极活泼分子。大多数IHC在室温下都是不稳定的，尤其是对于结构仍然未知的一氟化碘（IF）。在这里，我们通过扫描透射电子显微镜和电子能量损失光谱学，清楚地观察到了生长在WSe ₂表面的二维（2D）IF双层。双层IF显示出清晰的六边形晶格，并且与WSe ₂具有牢固的外延关系基质。尽管已知IF在-14°C时会升华，在环境条件下从未发现为固体形式，但令人惊讶的是，发现它稳定在合适的基材上，并且稳定的结构受到密度泛函理论的支持。这种IHC的2D形式实际上是在碱金属卤化物作为生长促进剂存在的情况下WSe ₂的化学气相沉积生长过程中的副产品，需要立即进行表面钝化来维持。这项工作指出了产生2D结构的巨大可能性，这些2D结构是无法预料的结晶或无法通过简单的剥离获得，而只能在特定的基板上生长。