Two-dimensional (2D) transition metal dichalcogenides (TMDs) manifest in various polymorphs, which deliver different electronic properties; the most prominent among them include the semiconducting 2H phase and metallic 1T (or distorted 1T′ phase) phase. Alkali metal intercalation or interface strain has been used to induce semiconductor-to-metal transition in a monolayer MoS₂ sheet, leading to exotic quantum states or improved performance in catalysis. However, the direct growth of 1T or 1T′ phase MoS₂ is challenging due to its metastability. Here, we report MBE growth of isolated 1T′ and 2H MoS₂ nanocrystals on a Au substrate; these nanocrystals can be differentiated unambiguously by their electronic states using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). By studying the initial stages of nucleation during molecular beam epitaxy (MBE) of MoS₂, we could identify atomic clusters (30–50 atoms) with intralayer stacking corresponding to 1T′ and 2H separately, which suggests a deterministic growth mechanism from initial nuclei. Furthermore, a topological insulator type behavior was observed for the 1T′ MoS₂ crystals, where an energy gap opening of 80 meV was measured by STS in the basal plane at 5 K, with the edge of the nanocrystals remaining metallic.

中文翻译：

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1T′相MoS ₂纳米晶体中空位开放的观察

二维（2D）过渡金属二硫化二氢（TMD）表现出各种多晶型物，它们提供了不同的电子特性。其中最突出的包括半导体2H相和金属1T（或扭曲的1T'相）相。碱金属插层或界面应变已用于在单层MoS ₂薄板中诱导半导体向金属的转变，从而导致奇特的量子态或改善了催化性能。然而，由于其亚稳性，1T或1T'相MoS ₂的直接生长具有挑战性。在这里，我们报告了孤立的1T'和2H MoS _2的MBE增长在金基底上的纳米晶体；这些纳米晶体可以使用扫描隧道显微镜（STM）和扫描隧道光谱（STS）通过其电子状态进行明确区分。通过研究MoS _2的分子束外延（MBE）过程中成核的初始阶段，我们可以识别具有分别对应于1T'和2H的层内堆叠的原子团簇（30-50个原子），这表明从初始原子核起确定的生长机理。此外，对于1T'MoS ₂晶体观察到拓扑绝缘体类型的行为，其中通过STS在5 K的基面上通过STS测量了80 meV的能隙开口，而纳米晶体的边缘仍然是金属。