Atomic resolution studies of 2D layered PtSe₂ crystals under in situ heating conditions are performed with an aberration corrected scanning transmission electron microscope (STEM). We reveal the temperature driven phase change in PtSe₂ driven by Se loss and stoichiometry modification. Annular dark field STEM (ADF-STEM) shows that the 1T PtSe₂ layered structure transforms into nonlayered PtSe crystals that are 2D and ultrathin. Above 500 °C, PtSe₂ rapidly transforms within minutes to this new phase. The detailed mechanism of this phase transformation is captured, revealing lateral diffusion and atomic digestion to yield PtSe crystals that are thicker than the original PtSe₂ layered precursor but shorter in width to conserve total atom number. A minimum thickness of the PtSe crystals is observed. The behavior of PtSe₂ is distinctly different from the phase transformations in the other Nobel metal chalcogenide PdSe₂ and in transition metal dichalcogenides, such as MoS₂ due to the presence of a stable 1:1 metal:chalcogen intermediate phase before pure metal formation during continuous vacancy addition. These results show how 2D layered precursor films can be transformed into stable nonlayered ultrathin crystals by depleting the chalcogen stoichiometry combined with thermally driven atomic migration.

中文翻译：

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2D少量层状1T PtSe ₂热转变为超薄2D非层状PtSe晶体的热驱动相变的原位原子尺度动力学

使用像差校正扫描透射电子显微镜（STEM）在原位加热条件下进行2D层状PtSe ₂晶体的原子分辨率研究。我们揭示了由Se损失和化学计量比变化驱动的PtSe ₂的温度驱动相变。环形暗场STEM（ADF-STEM）显示，1T PtSe _2的层状结构转变为2D和超薄的非层状PtSe晶体。高于500°C，PtSe ₂在几分钟之内迅速转变为这个新阶段。捕获了该相变的详细机制，揭示了横向扩散和原子消化作用，从而产生了比原始PtSe ₂还要厚的PtSe晶体。层状前体，但宽度较短，以节省总原子数。观察到PtSe晶体的最小厚度。PtSe ₂的行为与其他诺贝尔金属硫属元素化物PdSe ₂和过渡金属二硫属化物（例如MoS _2）中的相变明显不同，这是因为在形成纯金属期间，存在稳定的1：1金属：硫属元素中间相。持续增加空缺。这些结果表明，通过减少硫族元素化学计量与热驱动原子迁移的结合，可以将2D层状前体膜转变为稳定的无层超薄晶体。