Lead iodide (PbI₂), a typical layered semiconductor material, holds a wide visible band gap and a thickness-dependent band structure, which can be widely used in optical devices and perovskite solar cells. Although lead iodide is one of the most extensively studied materials, there is still a lack of experimental investigation of the electrical structure. In this study, we successfully grow the PbI₂ monolayer on the highly oriented pyrolytic graphite (HOPG) substrate by molecular beam epitaxy (MBE). Scanning tunneling microscopy (STM) characterization demonstrates the high-quality PbI₂ monolayer with a distinct Moiré pattern. Spectroscopic measurements reveal that the PbI₂ monolayer possesses a band gap of ∼2.98 eV in the visible purple range and a decreased band gap of ∼2.8 eV for the bilayer. Theoretical calculations corroborate the experiments and reveal an indirect-to-direct bandgap transition in the bilayer. This study has significant implications for the future field of optical devices.

中文翻译：

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外延原子厚碘化铅的晶体和电子结构


碘化铅（PbI ₂ ）是一种典型的层状半导体材料，具有较宽的可见带隙和厚度相关的能带结构，可广泛应用于光学器件和钙钛矿太阳能电池。尽管碘化铅是研究最广泛的材料之一，但仍然缺乏对其电结构的实验研究。在本研究中，我们通过分子束外延（MBE）成功在高取向热解石墨（HOPG）基板上生长了PbI ₂ 单层。扫描隧道显微镜 (STM) 表征表明高质量的 PbI ₂ 单层具有独特的莫尔图案。光谱测量表明，PbI ₂ 单层在可见紫色范围内具有~2.98 eV 的带隙，而双层的带隙则减小了~2.8 eV。理论计算证实了实验并揭示了双层中间接到直接带隙的转变。这项研究对未来的光学器件领域具有重要意义。